Showing 1–50 of 63 results for author: Gilad, S

Measuring short-range correlations and quasi-elastic cross sections in A(e,e') at x>1 and modest Q$^2$

Authors: Y. P. Zhang, Z. H. Ye, D. Nguyen, P. Aguilera, Z. Ahmed, H. Albataineh, K. Allada, B. Anderson, D. Anez, K. Aniol, J. Annand, J. Arrington, T. Averett, H. Baghdasaryan, X. Bai, A. Beck, S. Beck, V. Bellini, F. Benmokhtar, A. Camsonne, C. Chen, J. -P. Chen, K. Chirapatpimol, E. Cisbani, S. Covrig Dusa , et al. (74 additional authors not shown)

Abstract: We present results from the Jefferson Lab E08-014 experiment, investigating short-range correlations (SRC) through measurements of inclusive quasi-elastic scattering from $^2$H, $^3$He, $^4$He, $^{12}$C, $^{40}$Ca, and $^{48}$Ca. The kinematics were selected to isolate scattering from SRCs, yielding a plateau in the A/$^2$H cross-section ratios due to the universal two-body structure of the 2N-SRC… ▽ More We present results from the Jefferson Lab E08-014 experiment, investigating short-range correlations (SRC) through measurements of inclusive quasi-elastic scattering from $^2$H, $^3$He, $^4$He, $^{12}$C, $^{40}$Ca, and $^{48}$Ca. The kinematics were selected to isolate scattering from SRCs, yielding a plateau in the A/$^2$H cross-section ratios due to the universal two-body structure of the 2N-SRCs in light and heavy nuclei. We observe approximate plateaus in the A/$^2$H ratios and provide the first extractions of the A/$^2$H ratio for $^{40}$Ca and $^{48}$Ca. We also examine the A/$^3$He ratio, aiming to identify three-nucleon SRCs (3N-SRCs). Following the approach for isolating 2N-SRCs, searching for 3N-SRC dominance involved measuring the A/$^3$He cross section ratio at modest-to-large $Q^2$ values and looking for a plateau ratios for $x \gtorder 2.5$. This was not observed in the data, and in fact increasing $Q^2$ values moved the data \textit{further away} from the predicted plateau. We show here that, when analyzed in terms of the struck nucleon's light-cone momentum, the data exhibited the expected trend, progressively approaching the predicted 3N-SRC plateau. These observations suggest that future measurements at higher energies may facilitate a definitive isolation and identification of 3N-SRCs. △ Less

Submitted 14 December, 2025; v1 submitted 24 April, 2025; originally announced April 2025.

Comments: 10pages, 5 figures, accepted by Physics Letter B. Paper under production

The EMC Effect of Tritium and Helium-3 from the JLab MARATHON Experiment

Authors: D. Abrams, H. Albataineh, B. S. Aljawrneh, S. Alsalmi, D. Androic, K. Aniol, W. Armstrong, J. Arrington, H. Atac, T. Averett, C. Ayerbe Gayoso, X. Bai, J. Bane, S. Barcus, A. Beck, V. Bellini, H. Bhatt, D. Bhetuwal, D. Biswas, D. Blyth, W. Boeglin, D. Bulumulla, J. Butler, A. Camsonne, M. Carmignotto , et al. (109 additional authors not shown)

Abstract: Measurements of the EMC effect in the tritium and helium-3 mirror nuclei are reported. The data were obtained by the MARATHON Jefferson Lab experiment, which performed deep inelastic electron scattering from deuterium and the three-body nuclei, using a cryogenic gas target system and the High Resolution Spectrometers of the Hall A Facility of the Lab. The data cover the Bjorken $x$ range from 0.20… ▽ More Measurements of the EMC effect in the tritium and helium-3 mirror nuclei are reported. The data were obtained by the MARATHON Jefferson Lab experiment, which performed deep inelastic electron scattering from deuterium and the three-body nuclei, using a cryogenic gas target system and the High Resolution Spectrometers of the Hall A Facility of the Lab. The data cover the Bjorken $x$ range from 0.20 to 0.83, corresponding to a squared four-momentum transfer $Q^2$ range from 2.7 to $11.9\gevsq$, and to an invariant mass $W$ of the final hadronic state greater than 1.84 GeV/${\it c}^2$. The tritium EMC effect measurement is the first of its kind. The MARATHON experimental results are compared to results from previous measurements by DESY-HERMES and JLab-Hall C experiments, as well as with few-body theoretical predictions. △ Less

Submitted 15 October, 2024; originally announced October 2024.

Comments: arXiv admin note: text overlap with arXiv:2104.05850

Form Factors and Two-Photon Exchange in High-Energy Elastic Electron-Proton Scattering

Authors: M. E. Christy, T. Gautam, L. Ou, B. Schmookler, Y. Wang, D. Adikaram, Z. Ahmed, H. Albataineh, S. F. Ali, B. Aljawrneh, K. Allada, S. L. Allison, S. Alsalmi, D. Androic, K. Aniol, J. Annand, J. Arrington, H. Atac, T. Averett, C. Ayerbe Gayoso, X. Bai, J. Bane, S. Barcus, K. Bartlett, V. Bellini , et al. (145 additional authors not shown)

Abstract: We present new precision measurements of the elastic electron-proton scattering cross section for momentum transfer (Q$^2$) up to 15.75~\gevsq. Combined with existing data, these provide an improved extraction of the proton magnetic form factor at high Q$^2$ and double the range over which a longitudinal/transverse separation of the cross section can be performed. The difference between our result… ▽ More We present new precision measurements of the elastic electron-proton scattering cross section for momentum transfer (Q$^2$) up to 15.75~\gevsq. Combined with existing data, these provide an improved extraction of the proton magnetic form factor at high Q$^2$ and double the range over which a longitudinal/transverse separation of the cross section can be performed. The difference between our results and polarization data agrees with that observed at lower Q$^2$ and attributed to hard two-photon exchange (TPE) effects, extending to 8~(GeV/c)$^2$ the range of Q$^2$ for which a discrepancy is established at $>$95\% confidence. We use the discrepancy to quantify the size of TPE contributions needed to explain the cross section at high Q$^2$. △ Less

Submitted 21 March, 2022; v1 submitted 2 March, 2021; originally announced March 2021.

Comments: 7 pages, 2 figures

Journal ref: Phys. Rev. Lett. 128, 102002 (2022)

Modified Structure of Protons and Neutrons in Correlated Pairs

Authors: B. Schmookler, M. Duer, A. Schmidt, O. Hen, S. Gilad, E. Piasetzky, M. Strikman, L. B. Weinstein, The CLAS Collaboration

Abstract: The atomic nucleus is made of protons and neutrons (nucleons), that are themselves composed of quarks and gluons. Understanding how the quark-gluon structure of a nucleon bound in an atomic nucleus is modified by the surrounding nucleons is an outstanding challenge. Although evidence for such modification, known as the EMC effect, was first observed over 35 years ago, there is still no generally a… ▽ More The atomic nucleus is made of protons and neutrons (nucleons), that are themselves composed of quarks and gluons. Understanding how the quark-gluon structure of a nucleon bound in an atomic nucleus is modified by the surrounding nucleons is an outstanding challenge. Although evidence for such modification, known as the EMC effect, was first observed over 35 years ago, there is still no generally accepted explanation of its cause. Recent observations suggest that the EMC effect is related to close-proximity Short Range Correlated (SRC) nucleon pairs in nuclei. Here we report the first simultaneous, high-precision, measurements of the EMC effect and SRC abundances. We show that the EMC data can be explained by a universal modification of the structure of nucleons in neutron-proton (np) SRC pairs and present the first data-driven extraction of this universal modification function. This implies that, in heavier nuclei with many more neutrons than protons, each proton is more likely than each neutron to belong to an SRC pair and hence to have its quark structure distorted. △ Less

Submitted 25 April, 2020; originally announced April 2020.

Comments: Published in Nature. Total: 21 pages, 9 figures, 10 tables. Main text: 7 pages, 4 figures. Methods section: 1 page. Extended Data: 1 figure, 3 table. Supplementary Materials: 11 pages, 4 figures, 7 tables

Journal ref: Nature 566, 354 (2019)

Novel observation of isospin structure of short-range correlations in calcium isotopes

Authors: D. Nguyen, Z. Ye, P. Aguilera, Z. Ahmed, H. Albataineh, K. Allada, B. Anderson, D. Anez, K. Aniol, J. Annand, J. Arrington, T. Averett, H. Baghdasaryan, X. Bai, A. Beck, S. Beck, V. Bellini, F. Benmokhtar, A. Camsonne, C. Chen, J. -P. Chen, K. Chirapatpimol, E. Cisbani, M. M. Dalton, A. Daniel , et al. (79 additional authors not shown)

Abstract: Short Range Correlations (SRCs) have been identified as being responsible for the high momentum tail of the nucleon momentum distribution, n(k). Hard, short-range interactions of nucleon pairs generate the high momentum tail and imprint a universal character on n(k) for all nuclei at large momentum. Triple coincidence experiments have shown a strong dominance of np pairs, but these measurements in… ▽ More Short Range Correlations (SRCs) have been identified as being responsible for the high momentum tail of the nucleon momentum distribution, n(k). Hard, short-range interactions of nucleon pairs generate the high momentum tail and imprint a universal character on n(k) for all nuclei at large momentum. Triple coincidence experiments have shown a strong dominance of np pairs, but these measurements involve large final state interactions. This paper presents the results from Jefferson Lab experiment E08014 which measured inclusive electron scattering cross-section from Ca isotopes. By comparing the inclusive cross section from 48Ca to 40Ca in a kinematic region dominated by SRCs we provide a new way to study the isospin structure of SRCs. △ Less

Submitted 17 December, 2020; v1 submitted 23 April, 2020; originally announced April 2020.

Comments: 7 pages, 3 figures

Report number: JLAB-PHY-20-3177, DOE/OR/23177-4956

Journal ref: Phys. Rev. C 102, 064004 (2020)

Probing the core of the strong nuclear interaction

Authors: A. Schmidt, J. R. Pybus, R. Weiss, E. P. Segarra, A. Hrnjic, A. Denniston, O. Hen, E. Piasetzky, L. B. Weinstein, N. Barnea, M. Strikman, A. Larionov, D. Higinbotham, S. Adhikari, M. Amaryan, G. Angelini, G. Asryan, H. Atac, H. Avakian, C. Ayerbe Gayoso, L. Baashen, L. Barion, M. Bashkanov, M. Battaglieri, A. Beck , et al. (140 additional authors not shown)

Abstract: The strong nuclear interaction between nucleons (protons and neutrons) is the effective force that holds the atomic nucleus together. This force stems from fundamental interactions between quarks and gluons (the constituents of nucleons) that are described by the equations of Quantum Chromodynamics (QCD). However, as these equations cannot be solved directly, physicists resort to describing nuclea… ▽ More The strong nuclear interaction between nucleons (protons and neutrons) is the effective force that holds the atomic nucleus together. This force stems from fundamental interactions between quarks and gluons (the constituents of nucleons) that are described by the equations of Quantum Chromodynamics (QCD). However, as these equations cannot be solved directly, physicists resort to describing nuclear interactions using effective models that are well constrained at typical inter-nucleon distances in nuclei but not at shorter distances. This limits our ability to describe high-density nuclear matter such as in the cores of neutron stars. Here we use high-energy electron scattering measurements that isolate nucleon pairs in short-distance, high-momentum configurations thereby accessing a kinematical regime that has not been previously explored by experiments, corresponding to relative momenta above 400 MeV/c. As the relative momentum between two nucleons increases and their separation thereby decreases, we observe a transition from a spin-dependent tensor-force to a predominantly spin-independent scalar-force. These results demonstrate the power of using such measurements to study the nuclear interaction at short-distances and also support the use of point-like nucleons with two- and three-body effective interactions to describe nuclear systems up to densities several times higher than the central density of atomic nuclei. △ Less

Submitted 27 October, 2020; v1 submitted 23 April, 2020; originally announced April 2020.

Comments: Total 26 pages, 13 figures. Main text: 8 pages, 3 figures. Methods section: 6 pages. Extended Data: 8 figures, 1 table. Supplementary Materials: 8 pages, 2 figures

Journal ref: Nature vol. 578 pp. 540-544 (2020)

Probing few-body nuclear dynamics via 3H and 3He (e,e'p)pn cross-section measurements

Authors: R. Cruz-Torres, D. Nguyen, F. Hauenstein, A. Schmidt, S. Li, D. Abrams, H. Albataineh, S. Alsalmi, D. Androic, K. Aniol, W. Armstrong, J. Arrington, H. Atac, T. Averett, C. Ayerbe Gayoso, X. Bai, J. Bane, S. Barcus, A. Beck, V. Bellini, F. Benmokhtar, H. Bhatt, D. Bhetuwal, D. Biswas, D. Blyth , et al. (103 additional authors not shown)

Abstract: We report the first measurement of the \eep three-body breakup reaction cross sections in helium-3 ($^3$He) and tritium ($^3$H) at large momentum transfer ($\langle Q^2 \rangle \approx 1.9$ (GeV/c)$^2$) and $x_B>1$ kinematics, where the cross section should be sensitive to quasielastic (QE) scattering from single nucleons. The data cover missing momenta $40 \le p_{miss} \le 500$ MeV/c that, in the… ▽ More We report the first measurement of the \eep three-body breakup reaction cross sections in helium-3 ($^3$He) and tritium ($^3$H) at large momentum transfer ($\langle Q^2 \rangle \approx 1.9$ (GeV/c)$^2$) and $x_B>1$ kinematics, where the cross section should be sensitive to quasielastic (QE) scattering from single nucleons. The data cover missing momenta $40 \le p_{miss} \le 500$ MeV/c that, in the QE limit with no rescattering, equals the initial momentum of the probed nucleon. The measured cross sections are compared with state-of-the-art ab-initio calculations. Overall good agreement, within $\pm20\%$, is observed between data and calculations for the full $p_{miss}$ range for $^3$H and for $100 \le p_{miss} \le 350$ MeV/c for $^3$He. Including the effects of rescattering of the outgoing nucleon improves agreement with the data at $p_{miss} > 250$ MeV/c and suggests contributions from charge-exchange (SCX) rescattering. The isoscalar sum of $^3$He plus $^3$H, which is largely insensitive to SCX, is described by calculations to within the accuracy of the data over the entire $p_{miss}$ range. This validates current models of the ground state of the three-nucleon system up to very high initial nucleon momenta of $500$ MeV/c. △ Less

Submitted 17 June, 2020; v1 submitted 20 January, 2020; originally announced January 2020.

Comments: Accepted for publication in PRL. 8 pages, 3 figures, and online supplementary materials

Journal ref: Phys. Rev. Lett. 124, 212501 (2020)

Measurement of the single-spin asymmetry $A_y^0$ in quasi-elastic $^3$He$^\uparrow$($e,e'n$) scattering at $0.4 < Q^2 < 1.0$ GeV$/c^2$

Authors: E. Long, Y. W. Zhang, M. Mihoviloviv, G. Jin, V. Sulkosky, A. Kelleher, B. Anderson, D. W. Higinbotham, S. Sirca, K. Allada, J. R. M. Annand, T. Averett, W. Bertozzi, W. Boeglin, P. Bradshaw, A. Camsonne, M. Canan, G. D. Cates, C. Chen, J. -P. Chen, E. Chudakov, R. De Leo, X. Deng, A. Deur, C. Dutta , et al. (66 additional authors not shown)

Abstract: Due to the lack of free neutron targets, studies of the structure of the neutron are typically made by scattering electrons from either $^2$H or $^3$He targets. In order to extract useful neutron information from a $^3$He target, one must understand how the neutron in a $^3$He system differs from a free neutron by taking into account nuclear effects such as final state interactions and meson excha… ▽ More Due to the lack of free neutron targets, studies of the structure of the neutron are typically made by scattering electrons from either $^2$H or $^3$He targets. In order to extract useful neutron information from a $^3$He target, one must understand how the neutron in a $^3$He system differs from a free neutron by taking into account nuclear effects such as final state interactions and meson exchange currents. The target single spin asymmetry $A_y^0$ is an ideal probe of such effects, as any deviation from zero indicates effects beyond plane wave impulse approximation. New measurements of the target single spin asymmetry $A_y^0$ at $Q^2$ of 0.46 and 0.96 (GeV/$c)^2$ were made at Jefferson Lab using the quasi-elastic $^3\mathrm{He}^{\uparrow}(e,e'n)$ reaction. Our measured asymmetry decreases rapidly, from $>20\%$ at $Q^2=0.46$ (GeV/$c)^2$ to nearly zero at $Q^2=0.96$ (GeV$/c)^2$, demonstrating the fall-off of the reaction mechanism effects as $Q^2$ increases. We also observed a small $ε$-dependent increase in $A_y^0$ compared to previous measurements, particularly at moderate $Q^2$. This indicates that upcoming high $Q^2$ measurements from the Jefferson Lab 12 GeV program can cleanly probe neutron structure from polarized $^3$He using plane wave impulse approximation. △ Less

Submitted 10 June, 2019; originally announced June 2019.

Comments: 6 pages, 5 figures

Report number: JLAB-PHY-19-2949

Probing for high momentum protons in $^4$He via the $^4He(e,e'p)X$ reaction

Authors: S. Iqbal, F. Benmokhtar, M. Ivanov, N. See, K. Aniol, D. W. Higinbotham, C. Boyd, A. Gadsby, S. Gilad, A. Saha, J. M. Udias, J. S. Goodwill, D. Finton, A. Boyer, Z. Ye, P. Solvignon, P. Aguilera, Z. Ahmed, H. Albataineh, K. Allada, B. Anderson, D. Anez, J. Annand, J. Arrington, T. Averett , et al. (85 additional authors not shown)

Abstract: Experimental cross sections for the $^4He(e,e'p)X$ reaction up to a missing momentum of 0.632 GeV/$c$ at $x_B=1.24$ and $Q^2$=2(GeV/$c$)$^2$ are reported. The data are compared to Relativistic Distorted Wave Impulse Approximation(RDWIA) calculations for $^4He(e,e'p)^3H$ channel. Significantly more events in the triton mass region are measured for $p_{m}$$>$0.45 GeV/$c$ than are predicted by the th… ▽ More Experimental cross sections for the $^4He(e,e'p)X$ reaction up to a missing momentum of 0.632 GeV/$c$ at $x_B=1.24$ and $Q^2$=2(GeV/$c$)$^2$ are reported. The data are compared to Relativistic Distorted Wave Impulse Approximation(RDWIA) calculations for $^4He(e,e'p)^3H$ channel. Significantly more events in the triton mass region are measured for $p_{m}$$>$0.45 GeV/$c$ than are predicted by the theoretical model, suggesting that the effects of initial-state multi-nucleon correlations are stronger than expected by the RDWIA model. △ Less

Submitted 13 March, 2022; v1 submitted 1 May, 2019; originally announced May 2019.

Comments: Submitted to PRC

Report number: JLAB-PHY-19-2934

Comparing proton momentum distributions in $A=2$ and 3 nuclei via $^2$H $^3$H and $^3$He $(e, e'p)$ measurements

Authors: R. Cruz-Torres, S. Li, F. Hauenstein, A. Schmidt, D. Nguyen, D. Abrams, H. Albataineh, S. Alsalmi, D. Androic, K. Aniol, W. Armstrong, J. Arrington, H. Atac, T. Averett, C. Ayerbe Gayoso, X. Bai, J. Bane, S. Barcus, A. Beck, V. Bellini, H. Bhatt, D. Bhetuwal, D. Biswas, D. Blyth, W. Boeglin , et al. (103 additional authors not shown)

Abstract: We report the first measurement of the $(e,e'p)$ reaction cross-section ratios for Helium-3 ($^3$He), Tritium ($^3$H), and Deuterium ($d$). The measurement covered a missing momentum range of $40 \le p_{miss} \le 550$ MeV$/c$, at large momentum transfer ($\langle Q^2 \rangle \approx 1.9$ (GeV$/c$)$^2$) and $x_B>1$, which minimized contributions from non quasi-elastic (QE) reaction mechanisms. The… ▽ More We report the first measurement of the $(e,e'p)$ reaction cross-section ratios for Helium-3 ($^3$He), Tritium ($^3$H), and Deuterium ($d$). The measurement covered a missing momentum range of $40 \le p_{miss} \le 550$ MeV$/c$, at large momentum transfer ($\langle Q^2 \rangle \approx 1.9$ (GeV$/c$)$^2$) and $x_B>1$, which minimized contributions from non quasi-elastic (QE) reaction mechanisms. The data is compared with plane-wave impulse approximation (PWIA) calculations using realistic spectral functions and momentum distributions. The measured and PWIA-calculated cross-section ratios for $^3$He$/d$ and $^3$H$/d$ extend to just above the typical nucleon Fermi-momentum ($k_F \approx 250$ MeV$/c$) and differ from each other by $\sim 20\%$, while for $^3$He/$^3$H they agree within the measurement accuracy of about 3\%. At momenta above $k_F$, the measured $^3$He/$^3$H ratios differ from the calculation by $20\% - 50\%$. Final state interaction (FSI) calculations using the generalized Eikonal Approximation indicate that FSI should change the $^3$He/$^3$H cross-section ratio for this measurement by less than 5\%. If these calculations are correct, then the differences at large missing momenta between the $^3$He/$^3$H experimental and calculated ratios could be due to the underlying $NN$ interaction, and thus could provide new constraints on the previously loosely-constrained short-distance parts of the $NN$ interaction. △ Less

Submitted 24 September, 2019; v1 submitted 17 February, 2019; originally announced February 2019.

Comments: 8 pages, 3 figures (4 panels)

Report number: JLAB-PHY-19-2893; LA-UR-18-31091

Journal ref: Physics Letters B 797 (2019) 134890

Measurement of double-polarization asymmetries in the quasi-elastic $^3\vec{\mathrm{He}}(\vec{\mathrm{e}},\mathrm{e}'\mathrm{p})$ process

Authors: M. Mihovilovič, G. Jin, E. Long, Y. -W. Zhang, K. Allada, B. Anderson, J. R. M. Annand, T. Averett, W. Bertozzi, W. Boeglin, P. Bradshaw, A. Camsonne, M. Canan, G. D. Cates, C. Chen, J. P. Chen, E. Chudakov, R. De Leo, X. Deng, A. Deltuva, A. Deur, C. Dutta, L. El Fassi, D. Flay, S. Frullani , et al. (77 additional authors not shown)

Abstract: We report on a precise measurement of double-polarization asymmetries in electron-induced breakup of $^3\mathrm{He}$ proceeding to $\mathrm{pd}$ and $\mathrm{ppn}$ final states, performed in quasi-elastic kinematics at $Q^2 = 0.25\,(\mathrm{GeV}/c)^2$ for missing momenta up to $250\,\mathrm{MeV}/c$. These observables represent highly sensitive tools to investigate the electromagnetic and spin stru… ▽ More We report on a precise measurement of double-polarization asymmetries in electron-induced breakup of $^3\mathrm{He}$ proceeding to $\mathrm{pd}$ and $\mathrm{ppn}$ final states, performed in quasi-elastic kinematics at $Q^2 = 0.25\,(\mathrm{GeV}/c)^2$ for missing momenta up to $250\,\mathrm{MeV}/c$. These observables represent highly sensitive tools to investigate the electromagnetic and spin structure of $^3\mathrm{He}$ and the relative importance of two- and three-body effects involved in the breakup reaction dynamics. The measured asymmetries cannot be satisfactorily reproduced by state-of-the-art calculations of $^3\mathrm{He}$ unless their three-body segment is adjusted, indicating that the spin-dependent part of the nuclear interaction governing the three-body breakup process is much smaller than previously thought. △ Less

Submitted 17 April, 2018; originally announced April 2018.

Comments: 5 pages, 3 figures, submitted to Phys. Rev. Lett

Report number: JLAB-PHY-18-2681

Journal ref: Phys. Lett. B 788 (2019) 117

Search for three-nucleon short-range correlations in light nuclei

Authors: Z. Ye, P. Solvignon, D. Nguyen, P. Aguilera, Z. Ahmed, H. Albataineh, K. Allada, B. Anderson, D. Anez, K. Aniol, J. Annand, J. Arrington, T. Averett, H. Baghdasaryan, X. Bai, A. Beck, S. Beck, V. Bellini, F. Benmokhtar, A. Camsonne, C. Chen, J. -P. Chen, K. Chirapatpimol, E. Cisbani, M. M. Dalton , et al. (78 additional authors not shown)

Abstract: We present new data probing short-range correlations (SRCs) in nuclei through the measurement of electron scattering off high-momentum nucleons in nuclei. The inclusive 4He/3He cross section ratio is observed to be both x and Q2 independent for 1.5 < x < 2, confirming the dominance of two- nucleon (2N) short-range correlations (SRCs). For x > 2, our data do not support a previous claim of three-nu… ▽ More We present new data probing short-range correlations (SRCs) in nuclei through the measurement of electron scattering off high-momentum nucleons in nuclei. The inclusive 4He/3He cross section ratio is observed to be both x and Q2 independent for 1.5 < x < 2, confirming the dominance of two- nucleon (2N) short-range correlations (SRCs). For x > 2, our data do not support a previous claim of three-nucleon (3N) correlation dominance. While contributions beyond those from stationary 2N- SRCs are observed, our data show that isolating 3N-SRCs is more complicated than for 2N-SRCs. △ Less

Submitted 18 June, 2018; v1 submitted 19 December, 2017; originally announced December 2017.

Comments: 6 pages, 2 figures, new experimental results from JLab E08-014

Journal ref: Phys. Rev. C 97, 065204 (2018)

Isospin Dependence of the EMC effect and Short range Correlations

Authors: B. Schmookler, M. Duer, A. Schmidt, S. Gilad, L. B. Weinstein, E. Piasetzky, O. Hen

Abstract: Recent studies have shown that the per-nucleon number of Short-Range Correlated (SRC) pairs in nuclei and the strength of the EMC effect are linearly correlated, increasing from light nuclei up to iron and then saturating. This paper shows that the per-proton number of SRC pairs and the strength of the EMC effect are linearly correlated and increase from light to heavy asymmetric neutron-rich nucl… ▽ More Recent studies have shown that the per-nucleon number of Short-Range Correlated (SRC) pairs in nuclei and the strength of the EMC effect are linearly correlated, increasing from light nuclei up to iron and then saturating. This paper shows that the per-proton number of SRC pairs and the strength of the EMC effect are linearly correlated and increase from light to heavy asymmetric neutron-rich nuclei without saturation. These quantities, calculated per neutron, are also linearly related, but saturate (have constant value) remarkably early, starting with 12C. We propose that the observed phenomenological relationships indicate an isospin dependence of the EMC effect which is associated with the dominance of SRCs by neutron-proton pairs from 3He to heavy asymmetric neutron-rich nuclei. △ Less

Submitted 31 January, 2018; v1 submitted 2 November, 2017; originally announced November 2017.

Comments: Having discussed this work with the community, we found several shortcomings that require its withdrawal. There is no way to update it at the present time to address the issues raised. We therefore ask to withdraw it

Polarization Transfer Observables in Elastic Electron Proton Scattering at $Q^2 = $2.5, 5.2, 6.8, and 8.5 GeV$^2$

Authors: A. J. R. Puckett, E. J. Brash, M. K. Jones, W. Luo, M. Meziane, L. Pentchev, C. F. Perdrisat, V. Punjabi, F. R. Wesselmann, A. Afanasev, A. Ahmidouch, I. Albayrak, K. A. Aniol, J. Arrington, A. Asaturyan, H. Baghdasaryan, F. Benmokhtar, W. Bertozzi, L. Bimbot, P. Bosted, W. Boeglin, C. Butuceanu, P. Carter, S. Chernenko, E. Christy , et al. (82 additional authors not shown)

Abstract: The GEp-III and GEp-2$γ$ experiments were carried out in Jefferson Lab's (JLab's) Hall C from 2007-2008, to extend the knowledge of $G_E^p/G_M^p$ to the highest practically achievable $Q^2$ and to search for effects beyond the Born approximation in polarization transfer observables of elastic $\vec{e}p$ scattering. This article reports an expanded description of the common experimental apparatus a… ▽ More The GEp-III and GEp-2$γ$ experiments were carried out in Jefferson Lab's (JLab's) Hall C from 2007-2008, to extend the knowledge of $G_E^p/G_M^p$ to the highest practically achievable $Q^2$ and to search for effects beyond the Born approximation in polarization transfer observables of elastic $\vec{e}p$ scattering. This article reports an expanded description of the common experimental apparatus and data analysis procedure, and the results of a final reanalysis of the data from both experiments, including the previously unpublished results of the full-acceptance data of the GEp-2$γ$ experiment. The Hall C High Momentum Spectrometer detected and measured the polarization of protons recoiling elastically from collisions of JLab's polarized electron beam with a liquid hydrogen target. A large-acceptance electromagnetic calorimeter detected the elastically scattered electrons in coincidence to suppress inelastic backgrounds. The final GEp-III data are largely unchanged relative to the originally published results. The statistical uncertainties of the final GEp-2$γ$ data are significantly reduced at $ε= 0.632$ and $0.783$ relative to the original publication. The decrease with $Q^2$ of $G_E^p/G_M^p$ continues to $Q^2 = 8.5$ GeV$^2$, but at a slowing rate relative to the approximately linear decrease observed in earlier Hall A measurements. At $Q^2 = 2.5$ GeV$^2$, the proton form factor ratio $G_E^p/G_M^p$ shows no statistically significant $ε$-dependence, as expected in the Born approximation. The ratio $P_\ell/P_\ell^{Born}$ of the longitudinal polarization transfer component to its Born value shows an enhancement of roughly 1.4\% at $ε= 0.783$ relative to $ε= 0.149$, with $\approx 1.9σ$ significance based on the total uncertainty, implying a similar effect in the transverse component $P_t$ that cancels in the ratio $R$. △ Less

Submitted 10 August, 2018; v1 submitted 26 July, 2017; originally announced July 2017.

Comments: 44 pages, 28 figures. Archival publication for the GEp-III and GEp-2gamma experiments that ran in Jefferson Lab's experimental Hall C from October, 2007 to June, 2008. v2: final manuscript as accepted by PRC. v3: Replaced figures 13 and 19 with corrected versions from published Erratum. Also made minor corrections to the text and to Table XI reflecting the corrections in the published Erratum

Journal ref: Phys. Rev. C 96, 055203 (2017)

Technical Supplement to "Polarization Transfer Observables in Elastic Electron-Proton Scattering at Q$^2$ = 2.5, 5.2, 6.8, and 8.5 GeV$^2$"

Authors: A. J. R. Puckett, E. J. Brash, M. K. Jones, W. Luo, M. Meziane, L. Pentchev, C. F. Perdrisat, V. Punjabi, F. R. Wesselmann, A. Ahmidouch, I. Albayrak, K. A. Aniol, J. Arrington, A. Asaturyan, H. Baghdasaryan, F. Benmokhtar, W. Bertozzi, L. Bimbot, P. Bosted, W. Boeglin, C. Butuceanu, P. Carter, S. Chernenko, E. Christy, M. Commisso , et al. (81 additional authors not shown)

Abstract: The GEp-III and GEp-2$γ$ experiments, carried out in Jefferson Lab's Hall C from 2007-2008, consisted of measurements of polarization transfer in elastic electron-proton scattering at momentum transfers of $Q^2 = 2.5, 5.2, 6.8,$ and $8.54$ GeV$^2$. These measurements were carried out to improve knowledge of the proton electromagnetic form factor ratio $R = μ_p G_E^p/G_M^p$ at large values of… ▽ More The GEp-III and GEp-2$γ$ experiments, carried out in Jefferson Lab's Hall C from 2007-2008, consisted of measurements of polarization transfer in elastic electron-proton scattering at momentum transfers of $Q^2 = 2.5, 5.2, 6.8,$ and $8.54$ GeV$^2$. These measurements were carried out to improve knowledge of the proton electromagnetic form factor ratio $R = μ_p G_E^p/G_M^p$ at large values of $Q^2$ and to search for effects beyond the Born approximation in polarization transfer observables at $Q^2 = 2.5$ GeV$^2$. The final results of both experiments were reported in a recent archival publication. A full reanalysis of the data from both experiments was carried out in order to reduce the systematic and, for the GEp-2$γ$ experiment, statistical uncertainties. This technical note provides additional details of the final analysis omitted from the main publication, including the final evaluation of the systematic uncertainties. △ Less

Submitted 12 September, 2018; v1 submitted 24 July, 2017; originally announced July 2017.

Comments: 33 pages, 33 figures. v3 = Final manuscript as accepted for publication in Nuclear Instruments and Methods Section A (in press)

Report number: JLAB-PHY-18-2811

Measurement of the Vector and Tensor Asymmetries at Large Missing Momentum in Quasielastic $(\vec{e}, e^{\prime}p)$ Electron Scattering from Deuterium

Authors: A. DeGrush, A. Maschinot, T. Akdogan, R. Alarcon, W. Bertozzi, E. Booth, T. Botto, J. R. Calarco, B. Clasie, C. Crawford, K. Dow, M. Farkhondeh, R. Fatemi, O. Filoti, W. Franklin, H. Gao, E. Geis, S. Gilad, D. K. Hasell, P. Karpius, M. Kohl, H. Kolster, T. Lee, J. Matthews, K. McIlhany , et al. (19 additional authors not shown)

Abstract: We report the measurement of the beam-vector and tensor asymmetries $A^V_{ed}$ and $A^T_d$ in quasielastic $(\vec{e}, e^{\prime}p)$ electrodisintegration of the deuteron at the MIT-Bates Linear Accelerator Center up to missing momentum of 500~MeV/c. Data were collected simultaneously over a momentum transfer range $0.1< Q^2<0.5$~(GeV/c)$^2$ with the Bates Large Acceptance Spectrometer Toroid using… ▽ More We report the measurement of the beam-vector and tensor asymmetries $A^V_{ed}$ and $A^T_d$ in quasielastic $(\vec{e}, e^{\prime}p)$ electrodisintegration of the deuteron at the MIT-Bates Linear Accelerator Center up to missing momentum of 500~MeV/c. Data were collected simultaneously over a momentum transfer range $0.1< Q^2<0.5$~(GeV/c)$^2$ with the Bates Large Acceptance Spectrometer Toroid using an internal deuterium gas target, polarized sequentially in both vector and tensor states. The data are compared with calculations. The beam-vector asymmetry $A^V_{ed}$ is found to be directly sensitive to the $D$-wave component of the deuteron and have a zero-crossing at a missing momentum of about 320~MeV/c, as predicted. The tensor asymmetry $A^T_d$ at large missing momentum is found to be dominated by the influence of the tensor force in the neutron-proton final-state interaction. The new data provide a strong constraint on theoretical models. △ Less

Submitted 29 September, 2017; v1 submitted 10 July, 2017; originally announced July 2017.

Comments: 5 pages, 3 figures

Journal ref: Phys. Rev. Lett. 119, 182501 (2017)

Extraction of the Neutron Electric Form Factor from Measurements of Inclusive Double Spin Asymmetries

Authors: V. Sulkosky, G. Jin, E. Long, Y. W. Zhang, M. Mihovilovic, A. Kelleher, B. Anderson, D. W. Higinbotham, S. Sirca, K. Allada, J. R. M. Annand, T. Averett, W. Bertozzi, W. Boeglin, P. Bradshaw, A. Camsonne, M. Canan, G. D. Cates, C. Chen, J. -P. Chen, E. Chudakov, R. De Leo, X. Deng, A. Deur, C. Dutta , et al. (67 additional authors not shown)

Abstract: $[Background]$ Measurements of the neutron charge form factor, $G^n_E$, are challenging due to the fact that the neutron has no net charge. In addition, measurements of the neutron form factors must use nuclear targets which require accurately accounting for nuclear effects. Extracting $G^n_E$ with different targets and techniques provides an important test of our handling of these effects. $[Purp… ▽ More $[Background]$ Measurements of the neutron charge form factor, $G^n_E$, are challenging due to the fact that the neutron has no net charge. In addition, measurements of the neutron form factors must use nuclear targets which require accurately accounting for nuclear effects. Extracting $G^n_E$ with different targets and techniques provides an important test of our handling of these effects. $[Purpose]$ The goal of the measurement was to use an inclusive asymmetry measurement technique to extract the neutron charge form factor at a four-momentum transfer of $1~(\rm{GeV/c})^2$. This technique has very different systematic uncertainties than traditional exclusive measurements and thus serves as an independent check of whether nuclear effects have been taken into account correctly. $[Method]$ The inclusive quasi-elastic reaction $^3\overrightarrow{\rm{He}}(\overrightarrow{e},e')$ was measured at Jefferson Lab. The neutron electric form factor, $G_E^n$, was extracted at $Q^2 = 0.98~(\rm{GeV/c})^2$ from ratios of electron-polarization asymmetries measured for two orthogonal target spin orientations. This $Q^2$ is high enough that the sensitivity to $G_E^n$ is not overwhelmed by the neutron magnetic contribution, and yet low enough that explicit neutron detection is not required to suppress pion production. $[Results]$ The neutron electric form factor, $G_E^n$, was determined to be $0.0414\pm0.0077\;{(stat)}\pm0.0022\;{(syst)}$; providing the first high precision inclusive extraction of the neutron's charge form factor. $[Conclusions]$ The use of the inclusive quasi-elastic $^3\overrightarrow{\rm{He}}(\overrightarrow{e},e')$ with a four-momentum transfer near $1~(\rm{GeV/c})^2$ has been used to provide a unique measurement of $G^n_E$. This new result provides a systematically independent validation of the exclusive extraction technique results. △ Less

Submitted 28 November, 2017; v1 submitted 20 April, 2017; originally announced April 2017.

Comments: 7 pages, 2 figures, 2 tables

Report number: JLAB-PHY-17-2480

Journal ref: Phys. Rev. C 96, 065206 (2017)

First measurement of unpolarized SIDIS cross section and cross section ratios from a $^3$He target

Authors: X. Yan, K. Allada, K. Aniol, J. R. M. Annand, T. Averett, F. Benmokhtar, W. Bertozzi, P. C. Bradshaw, P. Bosted, A. Camsonne, M. Canan, G. D. Cates, C. Chen, J. -P. Chen, W. Chen, K. Chirapatpimol, E. Chudakov, E. Cisbani, J. C. Cornejo, F. Cusanno, M. M. Dalton, W. Deconinck, C. W. de Jager, R. De Leo, X. Deng , et al. (93 additional authors not shown)

Abstract: The unpolarized semi-inclusive deep-inelastic scattering (SIDIS) differential cross sections in $^3$He($e,e^{\prime}π^{\pm}$)$X$ have been measured for the first time in Jefferson Lab experiment E06-010 performed with a $5.9\,$GeV $e^-$ beam on a $^3$He target. The experiment focuses on the valence quark region, covering a kinematic range $0.12 < x_{bj} < 0.45$,… ▽ More The unpolarized semi-inclusive deep-inelastic scattering (SIDIS) differential cross sections in $^3$He($e,e^{\prime}π^{\pm}$)$X$ have been measured for the first time in Jefferson Lab experiment E06-010 performed with a $5.9\,$GeV $e^-$ beam on a $^3$He target. The experiment focuses on the valence quark region, covering a kinematic range $0.12 < x_{bj} < 0.45$, $1 < Q^2 < 4 \, \textrm{(GeV/c)}^2$, $0.45 < z_{h} < 0.65$, and $0.05 < P_t < 0.55 \, \textrm{GeV/c}$. The extracted SIDIS differential cross sections of $π^{\pm}$ production are compared with existing phenomenological models while the $^3$He nucleus approximated as two protons and one neutron in a plane wave picture, in multi-dimensional bins. Within the experimental uncertainties, the azimuthal modulations of the cross sections are found to be consistent with zero. △ Less

Submitted 15 November, 2016; v1 submitted 7 October, 2016; originally announced October 2016.

Journal ref: Phys. Rev. C 95, 035209 (2017)

Measurements of $d_{2}^{n}$ and $A_{1}^{n}$: Probing the neutron spin structure

Authors: D. Flay, M. Posik, D. S. Parno, K. Allada, W. Armstrong, T. Averett, F. Benmokhtar, W. Bertozzi, A. Camsonne, M. Canan, G. D. Cates, C. Chen, J. -P. Chen, S. Choi, E. Chudakov, F. Cusanno, M. M. Dalton, W. Deconinck, C. W. de Jager, X. Deng, A. Deur, C. Dutta, L. El Fassi, G. B. Franklin, M. Friend , et al. (66 additional authors not shown)

Abstract: We report on the results of the E06-014 experiment performed at Jefferson Lab in Hall A, where a precision measurement of the twist-3 matrix element $d_2$ of the neutron ($d_{2}^{n}$) was conducted. This quantity represents the average color Lorentz force a struck quark experiences in a deep inelastic electron scattering event off a neutron due to its interaction with the hadronizing remnants. Thi… ▽ More We report on the results of the E06-014 experiment performed at Jefferson Lab in Hall A, where a precision measurement of the twist-3 matrix element $d_2$ of the neutron ($d_{2}^{n}$) was conducted. This quantity represents the average color Lorentz force a struck quark experiences in a deep inelastic electron scattering event off a neutron due to its interaction with the hadronizing remnants. This color force was determined from a linear combination of the third moments of the spin structure functions $g_1$ and $g_2$ on $^{3}$He after nuclear corrections had been applied to these moments. The kinematics included two average $Q^{2}$ bins of $3.2$ GeV$^{2}$ and $4.3$ GeV$^{2}$, and Bjorken-$x$ $0.25 \leq x \leq 0.90$ covering the DIS and resonance regions. We found $d_2^n$ to be small and negative for $<Q^{2}> = 3.2$ GeV$^{2}$, and smaller for $<Q^{2}> = 4.3$ GeV$^{2}$, consistent with a lattice QCD calculation. The twist-4 matrix element $f_{2}^{n}$ was extracted by combining our $d_{2}^{n}$ with the world data on $Γ_{1}^{n} = \int_{0}^{1} g_{1}^{n} dx$. We found $f_{2}^{n}$ to be roughly an order of magnitude larger than $d_{2}^{n}$. Utilizing the extracted $d_{2}^{n}$ and $f_{2}^{n}$ data, we separated the color force into its electric and magnetic components, $F_{E}^{y,n}$ and $F_{B}^{y,n}$, and found them to be equal and opposite in magnitude, in agreement with instanton model predictions but not with those from QCD sum rules. Additionally, we have extracted the neutron virtual photon-nucleon asymmetry $A_{1}^{n}$, the structure function ratio $g_{1}^{n}/F_{1}^{n}$, and the quark ratios $(Δu + Δ\bar{u})/(u + \bar{u})$ and $(Δd + Δ\bar{d})/(d + \bar{d})$. These results were found to be consistent with DIS world data and with the prediction of the constituent quark model but at odds with those of perturbative QCD at large $x$. △ Less

Submitted 27 June, 2016; v1 submitted 11 March, 2016; originally announced March 2016.

Comments: 55 Pages, 45 figures, 48 tables. 15 supplemental files. Grammatical and typo fixes. Revised some model descriptions and updated analyses for f_2^n and color forces

Journal ref: Phys. Rev. D 94, 052003 (2016)

Electroexcitation of the $Δ^{+}(1232)$ at low momentum transfer

Authors: A. Blomberg, D. Anez, N. Sparveris, A. Sarty, M. Paolone, S. Gilad, D. Higinbotham, A. R. Abudureyimu, Z. Ahmed, H. Albataineh, K. Allada, B. Anderson, K. Aniol, J. Annand, T. Averett, H. Baghdasaryan, X. Bai, A. Beck, S. Beck, V. Bellini, F. Benmokhtar, W. Boeglin, C. M. Camacho, A. Camsonne, C. Chen , et al. (70 additional authors not shown)

Abstract: We report on new p$(e,e^\prime p)π^\circ$ measurements at the $Δ^{+}(1232)$ resonance at the low momentum transfer region. The mesonic cloud dynamics is predicted to be dominant and rapidly changing in this kinematic region offering a test bed for chiral effective field theory calculations. The new data explore the low $Q^2$ dependence of the resonant quadrupole amplitudes while extending the meas… ▽ More We report on new p$(e,e^\prime p)π^\circ$ measurements at the $Δ^{+}(1232)$ resonance at the low momentum transfer region. The mesonic cloud dynamics is predicted to be dominant and rapidly changing in this kinematic region offering a test bed for chiral effective field theory calculations. The new data explore the low $Q^2$ dependence of the resonant quadrupole amplitudes while extending the measurements of the Coulomb quadrupole amplitude to the lowest momentum transfer ever reached. The results disagree with predictions of constituent quark models and are in reasonable agreement with dynamical calculations that include pion cloud effects, chiral effective field theory and lattice calculations. The reported measurements suggest that improvement is required to the theoretical calculations and provide valuable input that will allow their refinements. △ Less

Submitted 2 June, 2016; v1 submitted 2 September, 2015; originally announced September 2015.

Measurement of the Target-Normal Single-Spin Asymmetry in Quasi-Elastic Scattering from the Reaction $^3$He$^\uparrow(e,e^\prime)$

Authors: Y. -W. Zhang, E. Long, M. Mihovilovič, G. Jin, K. Allada, B. Anderson, J. R. M. Annand, T. Averett, W. Boeglin, P. Bradshaw, A. Camsonne, M. Canan, G. D. Cates, C. Chen, J. P. Chen, E. Chudakov, R. De Leo, X. Deng, A. Deur, C. Dutta, L. El Fassi, D. Flay, S. Frullani, F. Garibaldi, H. Gao , et al. (67 additional authors not shown)

Abstract: We report the first measurement of the target single-spin asymmetry, $A_y$, in quasi-elastic scattering from the inclusive reaction $^3$He$^{\uparrow}(e,e^\prime)$ on a $^3$He gas target polarized normal to the lepton scattering plane. Assuming time-reversal invariance, this asymmetry is strictly zero for one-photon exchange. A non-zero $A_y$ can arise from the interference between the one- and tw… ▽ More We report the first measurement of the target single-spin asymmetry, $A_y$, in quasi-elastic scattering from the inclusive reaction $^3$He$^{\uparrow}(e,e^\prime)$ on a $^3$He gas target polarized normal to the lepton scattering plane. Assuming time-reversal invariance, this asymmetry is strictly zero for one-photon exchange. A non-zero $A_y$ can arise from the interference between the one- and two-photon exchange processes which is sensitive to the details of the sub-structure of the nucleon. An experiment recently completed at Jefferson Lab yielded asymmetries with high statistical precision at $Q^{2}=$ 0.13, 0.46 and 0.97 GeV$^{2}$. These measurements demonstrate, for the first time, that the $^3$He asymmetry is clearly non-zero and negative with a statistical significance of (8-10)$σ$. Using measured proton-to-$^{3}$He cross-section ratios and the effective polarization approximation, neutron asymmetries of $-$(1-3)% were obtained. The neutron asymmetry at high $Q^2$ is related to moments of the Generalized Parton Distributions (GPDs). Our measured neutron asymmetry at $Q^2=0.97$ GeV$^2$ agrees well with a prediction based on two-photon exchange using a GPD model and thus provides a new, independent constraint on these distributions. △ Less

Submitted 9 February, 2015; originally announced February 2015.

Journal ref: Phys. Rev. Lett. 115, 172502 (2015)

Double Spin Asymmetries of Inclusive Hadron Electroproductions from a Transversely Polarized $^3\rm{He}$ Target

Authors: The Jefferson Lab Hall A Collaboration, Y. X. Zhao, K. Allada, K. Aniol, J. R. M. Annand, T. Averett, F. Benmokhtar, W. Bertozzi, P. C. Bradshaw, P. Bosted, A. Camsonne, M. Canan, G. D. Cates, C. Chen, J. -P. Chen, W. Chen, K. Chirapatpimol, E. Chudakov, E. Cisbani, J. C. Cornejo, F. Cusanno, M. Dalton, W. Deconinck, C. W. de Jager, R. De Leo , et al. (92 additional authors not shown)

Abstract: We report the measurement of beam-target double-spin asymmetries ($A_\text{LT}$) in the inclusive production of identified hadrons, $\vec{e}~$+$~^3\text{He}^{\uparrow}\rightarrow h+X$, using a longitudinally polarized 5.9 GeV electron beam and a transversely polarized $^3\rm{He}$ target. Hadrons ($π^{\pm}$, $K^{\pm}$ and proton) were detected at 16$^{\circ}$ with an average momentum $<$$P_h$$>$=2.… ▽ More We report the measurement of beam-target double-spin asymmetries ($A_\text{LT}$) in the inclusive production of identified hadrons, $\vec{e}~$+$~^3\text{He}^{\uparrow}\rightarrow h+X$, using a longitudinally polarized 5.9 GeV electron beam and a transversely polarized $^3\rm{He}$ target. Hadrons ($π^{\pm}$, $K^{\pm}$ and proton) were detected at 16$^{\circ}$ with an average momentum $<$$P_h$$>$=2.35 GeV/c and a transverse momentum ($p_{T}$) coverage from 0.60 to 0.68 GeV/c. Asymmetries from the $^3\text{He}$ target were observed to be non-zero for $π^{\pm}$ production when the target was polarized transversely in the horizontal plane. The $π^{+}$ and $π^{-}$ asymmetries have opposite signs, analogous to the behavior of $A_\text{LT}$ in semi-inclusive deep-inelastic scattering. △ Less

Submitted 14 July, 2015; v1 submitted 4 February, 2015; originally announced February 2015.

Comments: Published in PRC (92.015207), nuclear experiment, high-energy experiment

Journal ref: PhysRevC.92.015207,2015

A precision measurement of the $p$($e,e^\prime p\,$)$π^0$ reaction at threshold

Authors: K. Chirapatpimol, M. H. Shabestari, R. A. Lindgren, L. C. Smith, J. R. M. Annand, D. W. Higinbotham, B. Moffit, V. Nelyubin, B. E. Norum, K. Allada, K. Aniol, K. Ardashev, D. S. Armstrong, R. A. Arndt, F. Benmokhtar, A. M. Bernstein, W. Bertozzi, W. J. Briscoe, L. Bimbot, A. Camsonne, J. -P. Chen, S. Choi, E. Chudakov, E. Cisbani, F. Cusanno , et al. (69 additional authors not shown)

Abstract: New results are reported from a measurement of $π^0$ electroproduction near threshold using the $p(e,e^{\prime} p)π^0$ reaction. The experiment was designed to determine precisely the energy dependence of $s-$ and $p-$wave electromagnetic multipoles as a stringent test of the predictions of Chiral Perturbation Theory (ChPT). The data were taken with an electron beam energy of 1192 MeV using a two-… ▽ More New results are reported from a measurement of $π^0$ electroproduction near threshold using the $p(e,e^{\prime} p)π^0$ reaction. The experiment was designed to determine precisely the energy dependence of $s-$ and $p-$wave electromagnetic multipoles as a stringent test of the predictions of Chiral Perturbation Theory (ChPT). The data were taken with an electron beam energy of 1192 MeV using a two-spectrometer setup in Hall A at Jefferson Lab. For the first time, complete coverage of the $φ^*_π$ and $θ^*_π$ angles in the $p π^0$ center-of-mass was obtained for invariant energies above threshold from 0.5 MeV up to 15 MeV. The 4-momentum transfer $Q^2$ coverage ranges from 0.05 to 0.155 (GeV/c)$^2$ in fine steps. A simple phenomenological analysis of our data shows strong disagreement with $p-$wave predictions from ChPT for $Q^2>0.07$ (GeV/c)$^2$, while the $s-$wave predictions are in reasonable agreement. △ Less

Submitted 10 April, 2015; v1 submitted 22 January, 2015; originally announced January 2015.

Comments: 5 pages, 6 figures

Journal ref: Phys. Rev. Lett. 114, 192503 (2015)

Momentum sharing in imbalanced Fermi systems

Authors: O. Hen, M. Sargsian, L. B. Weinstein, E. Piasetzky, H. Hakobyan, D. W. Higinbotham, M. Braverman, W. K. Brooks, S. Gilad, K. P. Adhikari, J. Arrington, G. Asryan, H. Avakian, J. Ball, N. A. Baltzell, M. Battaglieri, A. Beck, S. May-Tal Beck, I. Bedlinskiy, W. Bertozzi, A. Biselli, V. D. Burkert, T. Cao, D. S. Carman, A. Celentano , et al. (116 additional authors not shown)

Abstract: The atomic nucleus is composed of two different kinds of fermions, protons and neutrons. If the protons and neutrons did not interact, the Pauli exclusion principle would force the majority fermions (usually neutrons) to have a higher average momentum. Our high-energy electron scattering measurements using 12C, 27Al, 56Fe and 208Pb targets show that, even in heavy neutron-rich nuclei, short-range… ▽ More The atomic nucleus is composed of two different kinds of fermions, protons and neutrons. If the protons and neutrons did not interact, the Pauli exclusion principle would force the majority fermions (usually neutrons) to have a higher average momentum. Our high-energy electron scattering measurements using 12C, 27Al, 56Fe and 208Pb targets show that, even in heavy neutron-rich nuclei, short-range interactions between the fermions form correlated high-momentum neutron-proton pairs. Thus, in neutron-rich nuclei, protons have a greater probability than neutrons to have momentum greater than the Fermi momentum. This finding has implications ranging from nuclear few body systems to neutron stars and may also be observable experimentally in two-spin state, ultra-cold atomic gas systems. △ Less

Submitted 29 November, 2014; originally announced December 2014.

Comments: Published in Science. 10 pages, 3 figures

Journal ref: Science 346, 614 (2014)

Measurement of Parity-Violating Asymmetry in Electron-Deuteron Inelastic Scattering

Authors: D. Wang, K. Pan, R. Subedi, Z. Ahmed, K. Allada, K. A. Aniol, D. S. Armstrong, J. Arrington, V. Bellini, R. Beminiwattha, J. Benesch, F. Benmokhtar, W. Bertozzi, A. Camsonne, M. Canan, G. D. Cates, J. -P. Chen, E. Chudakov, E. Cisbani, M. M. Dalton, C. W. de Jager, R. De Leo, W. Deconinck, X. Deng, A. Deur , et al. (76 additional authors not shown)

Abstract: The parity-violating asymmetries between a longitudinally-polarized electron beam and an unpolarized deuterium target have been measured recently. The measurement covered two kinematic points in the deep inelastic scattering region and five in the nucleon resonance region. We provide here details of the experimental setup, data analysis, and results on all asymmetry measurements including parity-v… ▽ More The parity-violating asymmetries between a longitudinally-polarized electron beam and an unpolarized deuterium target have been measured recently. The measurement covered two kinematic points in the deep inelastic scattering region and five in the nucleon resonance region. We provide here details of the experimental setup, data analysis, and results on all asymmetry measurements including parity-violating electron asymmetries and those of inclusive pion production and beam-normal asymmetries. The parity-violating deep-inelastic asymmetries were used to extract the electron-quark weak effective couplings, and the resonance asymmetries provided the first evidence for quark-hadron duality in electroweak observables. These electron asymmetries and their interpretation were published earlier, but are presented here in more detail. △ Less

Submitted 12 November, 2014; originally announced November 2014.

Comments: 50 pages, submitted to Phys. Rev. C

Proton and Neutron Momentum Distributions in A = 3 Asymmetric Nuclei

Authors: O. Hen, L. B. Weinstein, S. Gilad, W. Boeglin

Abstract: A proposal approved by the Jefferson Lab (JLab) PAC to study the proton-to-neutron momentum distribution ratio in A=3 nuclei via (e,e'p) scattering off 3He and 3H mirror nuclei. The experiment will measure the 3H(e,e'p) and 3He(e,e'p) cross-sections and cross-section ratios at Q2 = 2 and xB>1 kinematics, over a missing momentum range of 0 - 450 MeV/c. The experiment was approved in 2014 at part of… ▽ More A proposal approved by the Jefferson Lab (JLab) PAC to study the proton-to-neutron momentum distribution ratio in A=3 nuclei via (e,e'p) scattering off 3He and 3H mirror nuclei. The experiment will measure the 3H(e,e'p) and 3He(e,e'p) cross-sections and cross-section ratios at Q2 = 2 and xB>1 kinematics, over a missing momentum range of 0 - 450 MeV/c. The experiment was approved in 2014 at part of the JLab Hall-A Tritium run period for a total run time of 12 days. △ Less

Submitted 16 October, 2014; originally announced October 2014.

Comments: A proposal approved by the Jefferson Lab PAC

Measurement of double-polarization asymmetries in the quasi-elastic $^3\vec{\mathrm{He}}(\vec{\mathrm{e}},\mathrm{e}'\mathrm{d})$ process

Authors: The Jefferson Lab Hall A Collaboration, M. Mihovilovič, G. Jin, E. Long, Y. -W. Zhang, K. Allada, B. Anderson, J. R. M. Annand, T. Averett, W. Boeglin, P. Bradshaw, A. Camsonne, M. Canan, G. D. Cates, C. Chen, J. P. Chen, E. Chudakov, R. De Leo, X. Deng, A. Deltuva, A. Deur, C. Dutta, L. El Fassi, D. Flay, S. Frullani , et al. (74 additional authors not shown)

Abstract: We present a precise measurement of double-polarization asymmetries in the $^3\vec{\mathrm{He}}(\vec{\mathrm{e}},\mathrm{e}'\mathrm{d})$ reaction. This particular process is a uniquely sensitive probe of hadron dynamics in $^3\mathrm{He}$ and the structure of the underlying electromagnetic currents. The measurements have been performed in and around quasi-elastic kinematics at… ▽ More We present a precise measurement of double-polarization asymmetries in the $^3\vec{\mathrm{He}}(\vec{\mathrm{e}},\mathrm{e}'\mathrm{d})$ reaction. This particular process is a uniquely sensitive probe of hadron dynamics in $^3\mathrm{He}$ and the structure of the underlying electromagnetic currents. The measurements have been performed in and around quasi-elastic kinematics at $Q^2 = 0.25\,(\mathrm{GeV}/c)^2$ for missing momenta up to $270\,\mathrm{MeV}/c$. The asymmetries are in fair agreement with the state-of-the-art calculations in terms of their functional dependencies on $p_\mathrm{m}$ and $ω$, but are systematically offset. Beyond the region of the quasi-elastic peak, the discrepancies become even more pronounced. Thus, our measurements have been able to reveal deficiencies in the most sophisticated calculations of the three-body nuclear system, and indicate that further refinement in the treatment of their two- and/or three-body dynamics is required. △ Less

Submitted 23 October, 2014; v1 submitted 8 September, 2014; originally announced September 2014.

Comments: 6 pages, 4 figures, accepted for publication at Phys. Rev. Lett

Journal ref: Phys. Rev. Lett. 113, 232505 (2014)

In Medium Nucleon Structure Functions, SRC, and the EMC effect

Authors: O. Hen, L. B. Weinstein, S. Gilad, S. A. Wood

Abstract: A proposal approved by the Jefferson Lab PAC to study semi-inclusive deep inelastic scattering (DIS) off the deuteron, tagged with high momentum recoiling protons or neutrons emitted at large angle relative to the momentum transfer. This experiment aims at studying the virtuality dependence of the bound nucleon structure function as a possible cause to the EMC effect and the EMC-SRC correlations.… ▽ More A proposal approved by the Jefferson Lab PAC to study semi-inclusive deep inelastic scattering (DIS) off the deuteron, tagged with high momentum recoiling protons or neutrons emitted at large angle relative to the momentum transfer. This experiment aims at studying the virtuality dependence of the bound nucleon structure function as a possible cause to the EMC effect and the EMC-SRC correlations. The experiment was approved in 2011 for a total run time of 40 days. △ Less

Submitted 5 September, 2014; originally announced September 2014.

Comments: A proposal approved by the Jefferson Lab PAC

Precision Measurements of $A_1^n$ in the Deep Inelastic Regime

Authors: D. S. Parno, D. Flay, M. Posik, K. Allada, W. Armstrong, T. Averett, F. Benmokhtar, W. Bertozzi, A. Camsonne, M. Canan, G. D. Cates, C. Chen, J. -P. Chen, S. Choi, E. Chudakov, F. Cusanno, M. M. Dalton, W. Deconinck, C. W. de Jager, X. Deng, A. Deur, C. Dutta, L. El Fassi, G. B. Franklin, M. Friend , et al. (67 additional authors not shown)

Abstract: We have performed precision measurements of the double-spin virtual-photon asymmetry $A_1$ on the neutron in the deep inelastic scattering regime, using an open-geometry, large-acceptance spectrometer. Our data cover a wide kinematic range $0.277 \leq x \leq 0.548$ at an average $Q^2$ value of 3.078~(GeV/c)$^2$, doubling the available high-precision neutron data in this $x$ range. We have combined… ▽ More We have performed precision measurements of the double-spin virtual-photon asymmetry $A_1$ on the neutron in the deep inelastic scattering regime, using an open-geometry, large-acceptance spectrometer. Our data cover a wide kinematic range $0.277 \leq x \leq 0.548$ at an average $Q^2$ value of 3.078~(GeV/c)$^2$, doubling the available high-precision neutron data in this $x$ range. We have combined our results with world data on proton targets to extract the ratio of polarized-to-unpolarized parton distribution functions for up quarks and for down quarks in the same kinematic range. Our data are consistent with a previous observation of an $A_1^n$ zero crossing near $x=0.5$. We find no evidence of a transition to a positive slope in $(Δd + Δ\bar{d})/(d + \bar{d})$ up to $x=0.548$. △ Less

Submitted 1 August, 2019; v1 submitted 4 June, 2014; originally announced June 2014.

Comments: 6 pages, 2 figures, 3 tables. Two typos corrected in Table 3

Single Spin Asymmetries in Charged Kaon Production from Semi-Inclusive Deep Inelastic Scattering on a Transversely Polarized $^3{\rm{He}}$ Target

Authors: Y. X. Zhao, Y. Wang, K. Allada, K. Aniol, J. R. M. Annand, T. Averett, F. Benmokhtar, W. Bertozzi, P. C. Bradshaw, P. Bosted, A. Camsonne, M. Canan, G. D. Cates, C. Chen, J. -P. Chen, W. Chen, K. Chirapatpimol, E. Chudakov, E. Cisbani, J. C. Cornejo, F. Cusanno, M. M. Dalton, W. Deconinck, C. W. de Jager, R. De Leo , et al. (91 additional authors not shown)

Abstract: We report the first measurement of target single spin asymmetries of charged kaons produced in semi-inclusive deep inelastic scattering of electrons off a transversely polarized $^3{\rm{He}}$ target. Both the Collins and Sivers moments, which are related to the nucleon transversity and Sivers distributions, respectively, are extracted over the kinematic range of 0.1$<$$x_{bj}$$<$0.4 for $K^{+}$ an… ▽ More We report the first measurement of target single spin asymmetries of charged kaons produced in semi-inclusive deep inelastic scattering of electrons off a transversely polarized $^3{\rm{He}}$ target. Both the Collins and Sivers moments, which are related to the nucleon transversity and Sivers distributions, respectively, are extracted over the kinematic range of 0.1$<$$x_{bj}$$<$0.4 for $K^{+}$ and $K^{-}$ production. While the Collins and Sivers moments for $K^{+}$ are consistent with zero within the experimental uncertainties, both moments for $K^{-}$ favor negative values. The Sivers moments are compared to the theoretical prediction from a phenomenological fit to the world data. While the $K^{+}$ Sivers moments are consistent with the prediction, the $K^{-}$ results differ from the prediction at the 2-sigma level. △ Less

Submitted 28 April, 2014; originally announced April 2014.

Comments: 6 pages, 3 figures

Journal ref: Phys. Rev. C.90.055201, 2014

A Precision Measurement of the Neutron Twist-3 Matrix Element $d_2^n$: Probing Color Forces

Authors: M. Posik, D. Flay, D. S. Parno, K. Allada, W. Armstrong, T. Averett, F. Benmokhtar, W. Bertozzi, A. Camsonne, M. Canan, G. D. Cates, C. Chen, J. -P. Chen, S. Choi, E. Chudakov, F. Cusanno, M. M. Dalton, W. Deconinck, C. W. de Jager, X. Deng, A. Deur, C. Dutta, L. El Fassi, G. B. Franklin, M. Friend , et al. (67 additional authors not shown)

Abstract: Double-spin asymmetries and absolute cross sections were measured at large Bjorken $x$ (0.25 $ \le x \le $ 0.90), in both the deep-inelastic and resonance regions, by scattering longitudinally polarized electrons at beam energies of 4.7 and 5.9 GeV from a transversely and longitudinally polarized $^3$He target. In this dedicated experiment, the spin structure function $g_2$ on $^3$He was determine… ▽ More Double-spin asymmetries and absolute cross sections were measured at large Bjorken $x$ (0.25 $ \le x \le $ 0.90), in both the deep-inelastic and resonance regions, by scattering longitudinally polarized electrons at beam energies of 4.7 and 5.9 GeV from a transversely and longitudinally polarized $^3$He target. In this dedicated experiment, the spin structure function $g_2$ on $^3$He was determined with precision at large $x$, and the neutron twist-three matrix element $d_2^n$ was measured at $\left< Q^2\right>$ of 3.21 and 4.32 GeV$^2$/$c^2$, with an absolute precision of about $10^{-5}$. Our results are found to be in agreement with lattice QCD calculations and resolve the disagreement found with previous data at $\left< Q^2\right> =$ 5 GeV$^2$/$c^2$. Combining $d_2^n$ and a newly extracted twist-four matrix element, $f_2^n$, the average neutron color electric and magnetic forces were extracted and found to be of opposite sign and about 30 MeV/fm in magnitude. △ Less

Submitted 3 July, 2014; v1 submitted 15 April, 2014; originally announced April 2014.

Comments: Corrected a typo in the author list and Figure 1 legend. 6 pages, 2 figures, 2 tables

Probing the Repulsive Core of the Nucleon-Nucleon Interaction via the 4He(e,e'pN) Triple-Coincidence Reaction

Authors: I. Korover N. Muangma, O. Hen, R. Shneor, V. Sulkosky, A. Kelleher, S. Gilad, D. W. Higinbotham, E. Piasetzky J. Watson, S. Wood, Abdurahim Rakhman, P. Aguilera, Z. Ahmed, H. Albataineh, K. Allada, B. Anderson, D. Anez, K. Aniol, J. Annand, W. Armstrong, J. Arrington, T. Averett, T. Badman, H. Baghdasaryan, X. Bai, A. Beck , et al. (93 additional authors not shown)

Abstract: We studied simultaneously the 4He(e,e'p), 4He(e,e'pp), and 4He(e,e'pn) reactions at Q^2=2 [GeV/c]2 and x_B>1, for a (e,e'p) missing-momentum range of 400 to 830 MeV/c. The knocked-out proton was detected in coincidence with a proton or neutron recoiling almost back to back to the missing momentum, leaving the residual A=2 system at low excitation energy. These data were used to identify two-nucleo… ▽ More We studied simultaneously the 4He(e,e'p), 4He(e,e'pp), and 4He(e,e'pn) reactions at Q^2=2 [GeV/c]2 and x_B>1, for a (e,e'p) missing-momentum range of 400 to 830 MeV/c. The knocked-out proton was detected in coincidence with a proton or neutron recoiling almost back to back to the missing momentum, leaving the residual A=2 system at low excitation energy. These data were used to identify two-nucleon short-range correlated pairs and to deduce their isospin structure as a function of missing momentum in a region where the nucleon-nucleon force is expected to change from predominantly tensor to repulsive. Neutron-proton pairs dominate the high-momentum tail of the nucleon momentum distributions, but their abundance is reduced as the nucleon momentum increases beyond ~500 MeV/c. The extracted fraction of proton-proton pairs is small and almost independent of the missing momentum in the range we studied. Our data are compared with ab-initio calculations of two-nucleon momentum distributions in 4He. △ Less

Submitted 11 July, 2014; v1 submitted 23 January, 2014; originally announced January 2014.

Comments: 6 pages, 2 figures

Report number: JLAB-PHY-14-1862

Journal ref: Phys. Rev. Lett. 113, 022501 (2014)

Measurement of pretzelosity asymmetry of charged pion production in Semi-Inclusive Deep Inelastic Scattering on a polarized $^3$He target

Authors: Y. Zhang, X. Qian, K. Allada, C. Dutta, J. Huang, J. Katich, Y. Wang, K. Aniol, J. R. M. Annand, T. Averett, F. Benmokhtar, W. Bertozzi, P. C. Bradshaw, P. Bosted, A. Camsonne, M. Canan, G. D. Cates, C. Chen, J. -P. Chen, W. Chen, K. Chirapatpimol, E. Chudakov, E. Cisbani, J. C. Cornejo, F. Cusanno , et al. (90 additional authors not shown)

Abstract: An experiment to measure single-spin asymmetries in semi-inclusive production of charged pions in deep-inelastic scattering on a transversely polarized $^3$He target was performed at Jefferson Lab in the kinematic region of $0.16<x<0.35$ and $1.4<Q^2<2.7$ ${\rm GeV^2}$. The pretzelosity asymmetries on $^3$He, which can be expressed as the convolution of the $h^\perp_{1T}$ transverse momentum depen… ▽ More An experiment to measure single-spin asymmetries in semi-inclusive production of charged pions in deep-inelastic scattering on a transversely polarized $^3$He target was performed at Jefferson Lab in the kinematic region of $0.16<x<0.35$ and $1.4<Q^2<2.7$ ${\rm GeV^2}$. The pretzelosity asymmetries on $^3$He, which can be expressed as the convolution of the $h^\perp_{1T}$ transverse momentum dependent distribution functions and the Collins fragmentation functions in the leading order, were measured for the first time. Using the effective polarization approximation, we extracted the corresponding neutron asymmetries from the measured $^3$He asymmetries and cross-section ratios between the proton and $^3$He. Our results show that for both $π^{\pm}$ on $^3$He and on the neutron the pretzelosity asymmetries are consistent with zero within experimental uncertainties. △ Less

Submitted 15 December, 2013; v1 submitted 11 December, 2013; originally announced December 2013.

Comments: 6 pages, 3 figures; enlarged the legends in Fig.3; added 3 citations

Journal ref: Phys. Rev. C 90, 055209 (2014)

Single Spin Asymmetries of Inclusive Hadrons Produced in Electron Scattering from a Transversely Polarized $^3$He Target

Authors: K. Allada, Y. X. Zhao, K. Aniol, J. R. M. Annand, T. Averett, F. Benmokhtar, W. Bertozzi, P. C. Bradshaw, P. Bosted, A. Camsonne, M. Canan, G. D. Cates, C. Chen, J. -P. Chen, W. Chen, K. Chirapatpimol, E. Chudakov, E. Cisbani, J. C. Cornejo, F. Cusanno, M. Dalton, W. Deconinck, C. W. de Jager, R. De Leo, X. Deng , et al. (91 additional authors not shown)

Abstract: We report the first measurement of target single-spin asymmetries (A$_N$) in the inclusive hadron production reaction, $e~$+$~^3\text{He}^{\uparrow}\rightarrow h+X$, using a transversely polarized $^3$He target. The experiment was conducted at Jefferson Lab in Hall A using a 5.9-GeV electron beam. Three types of hadrons ($π^{\pm}$, $\text{K}^{\pm}$ and proton) were detected in the transverse hadro… ▽ More We report the first measurement of target single-spin asymmetries (A$_N$) in the inclusive hadron production reaction, $e~$+$~^3\text{He}^{\uparrow}\rightarrow h+X$, using a transversely polarized $^3$He target. The experiment was conducted at Jefferson Lab in Hall A using a 5.9-GeV electron beam. Three types of hadrons ($π^{\pm}$, $\text{K}^{\pm}$ and proton) were detected in the transverse hadron momentum range 0.54 $<p_T<$ 0.74 GeV/c. The range of $x_F$ for pions was -0.29 $<x_F<$ -0.23 and for kaons -0.25 $<x_F<$-0.18. The observed asymmetry strongly depends on the type of hadron. A positive asymmetry is observed for $π^+$ and $\text{K}^+$. A negative asymmetry is observed for $π^{-}$. The magnitudes of the asymmetries follow $|A^{π^-}| < |A^{π^+}| < |A^{K^+}|$. The K$^{-}$ and proton asymmetries are consistent with zero within the experimental uncertainties. The $π^{+}$ and $π^{-}$ asymmetries measured for the $^3$He target and extracted for neutrons are opposite in sign with a small increase observed as a function of $p_T$. △ Less

Submitted 18 March, 2014; v1 submitted 7 November, 2013; originally announced November 2013.

Comments: Updated version, submitted to Phys. Rev. C

Journal ref: Phys. Rev. C 89, 042201(R), 2014

Measurement of the Target-Normal Single-Spin Asymmetry in Deep-Inelastic Scattering from the Reaction $^{3}\mathrm{He}^{\uparrow}(e,e')X$

Authors: J. Katich, X. Qian, Y. X. Zhao, K. Allada, K. Aniol, J. R. M. Annand, T. Averett, F. Benmokhtar, W. Bertozzi, P. C. Bradshaw, P. Bosted, A. Camsonne, M. Canan, G. D. Cates, C. Chen, J. -P. Chen, W. Chen, K. Chirapatpimol, E. Chudakov, E. Cisbani, J. C. Cornejo, F. Cusanno, M. M. Dalton, W. Deconinck, C. W. de Jager , et al. (91 additional authors not shown)

Abstract: We report the first measurement of the target-normal single-spin asymmetry in deep-inelastic scattering from the inclusive reaction $^3$He$^{\uparrow}\left(e,e' \right)X$ on a polarized $^3$He gas target. Assuming time-reversal invariance, this asymmetry is strictly zero in the Born approximation but can be non-zero if two-photon-exchange contributions are included. The experiment, conducted at Je… ▽ More We report the first measurement of the target-normal single-spin asymmetry in deep-inelastic scattering from the inclusive reaction $^3$He$^{\uparrow}\left(e,e' \right)X$ on a polarized $^3$He gas target. Assuming time-reversal invariance, this asymmetry is strictly zero in the Born approximation but can be non-zero if two-photon-exchange contributions are included. The experiment, conducted at Jefferson Lab using a 5.89 GeV electron beam, covers a range of $1.7 < W < 2.9$ GeV, $1.0<Q^2<4.0$ GeV$^2$ and $0.16<x<0.65$. Neutron asymmetries were extracted using the effective nucleon polarization and measured proton-to-$^3$He cross section ratios. The measured neutron asymmetries are negative with an average value of $(-1.09 \pm 0.38) \times10^{-2}$ for invariant mass $W>2$ GeV, which is non-zero at the $2.89σ$ level. Our measured asymmetry agrees both in sign and magnitude with a two-photon-exchange model prediction that uses input from the Sivers transverse momentum distribution obtained from semi-inclusive deep-inelastic scattering. △ Less

Submitted 4 August, 2014; v1 submitted 1 November, 2013; originally announced November 2013.

Comments: This is the final edited version as published in PRL

Journal ref: Phys. Rev. Lett. 113, 022502 (2014)

Studying the Proton "Radius" Puzzle with μp Elastic Scattering

Authors: R. Gilman, E. J. Downie, G. Ron, A. Afanasev, J. Arrington, O. Ates, F. Benmokhtar, J. Bernauer, E. Brash, W. J. Briscoe, K. Deiters, J. Diefenbach, C. Djalali, B. Dongwi, L. El Fassi, S. Gilad, K. Gnanvo, R. Gothe, D. Higinbotham, R. Holt, Y. Ilieva, H. Jiang, M. Kohl, G. Kumbartzki, J. Lichtenstadt , et al. (23 additional authors not shown)

Abstract: The Proton Radius Puzzle is the inconsistency between the proton radius determined from muonic hydrogen and the proton radius determined from atomic hydrogen level transitions and ep elastic scattering. No generally accepted resolution to the Puzzle has been found. Possible solutions generally fall into one of three categories: the two radii are different due to novel beyond-standard-model physics… ▽ More The Proton Radius Puzzle is the inconsistency between the proton radius determined from muonic hydrogen and the proton radius determined from atomic hydrogen level transitions and ep elastic scattering. No generally accepted resolution to the Puzzle has been found. Possible solutions generally fall into one of three categories: the two radii are different due to novel beyond-standard-model physics, the two radii are different due to novel aspects of nucleon structure, and the two radii are the same, but there are underestimated uncertainties or other issues in the ep experiments. The MUon proton Scattering Experiment (MUSE) at the Paul Scherrer Institut is a simultaneous measurement of μ^+ p and e^+ p elastic scattering, as well as μ^- p and e^- p elastic scattering, which will allow a determination of the consistency of the μp and the ep interactions. The differences between + and - charge scattering are sensitive to two-photon exchange effects, higher-order corrections to the scattering process. The slopes of the cross sections as Q^2 -> 0 determine the proton "radius". We plan to measure relative cross sections at a typical level of a few tenths of a percent, which should allow the proton radius to be determined at the level of ~0.01 fm, similar to previous ep measurements. The measurements will test several possible explanations of the proton radius puzzle, including some models of beyond-standard-model physics, some models of novel hadronic physics, and some issues in the radius extraction from scattering data. △ Less

Submitted 29 July, 2013; v1 submitted 8 March, 2013; originally announced March 2013.

Comments: 22 pages, 3 figures. This is a "White Paper" on the Paul Scherrer Institut MUSE experiment. Fixed references in version 2. Author list corrections

Measurement of the 12C(e,e'p)11B Two-Body Breakup Reaction at High Missing Momentum Values

Authors: P. Monaghan, R. Shneor, R. Subedi, B. D. Anderson, K. Aniol, J. Annand, J. Arrington, H. Benaoum, F. Benmokhtar, P. Bertin, W. Bertozzi, W. Boeglin, J. P. Chen, Seonho Choi, E. Chudakov, C. Ciofi degli Atti, E. Cisbani, W. Cosyn, B. Craver, C. W. de Jager, R. J. Feuerbach, E. Folts, S. Frullani, F. Garibaldi, O. Gayou , et al. (59 additional authors not shown)

Abstract: The five-fold differential cross section for the 12C(e,e'p)11B reaction was determined over a missing momentum range of 200-400 MeV/c, in a kinematics regime with Bjorken x > 1 and Q2 = 2.0 (GeV/c)2. A comparison of the results and theoretical models and previous lower missing momentum data is shown. The theoretical calculations agree well with the data up to a missing momentum value of 325 MeV/c… ▽ More The five-fold differential cross section for the 12C(e,e'p)11B reaction was determined over a missing momentum range of 200-400 MeV/c, in a kinematics regime with Bjorken x > 1 and Q2 = 2.0 (GeV/c)2. A comparison of the results and theoretical models and previous lower missing momentum data is shown. The theoretical calculations agree well with the data up to a missing momentum value of 325 MeV/c and then diverge for larger missing momenta. The extracted distorted momentum distribution is shown to be consistent with previous data and extends the range of available data up to 400 MeV/c. △ Less

Submitted 16 June, 2014; v1 submitted 29 January, 2013; originally announced January 2013.

Comments: 12 pages, 1 table and 3 figures for submission to Journal Physics G

Report number: JLAB-PHY-13-1683

Journal ref: J. Phys. G: Nucl. Part. Phys. 41 (2014) 105109

Measurement of transparency ratios for protons from short-range correlated pairs

Authors: O. Hen, H. Hakobyan, R. Shneor, E. Piasetzky, L. B. Weinstein, W. K. Brooks, S. May-Tal Beck, S. Gilad

Abstract: Nuclear transparency, Tp(A), is a measure of the average probability for a struck proton to escape the nucleus without significant re-interaction. Previously, nuclear transparencies were extructed for quasi-elastic A(e,e'p) knockout of protons with momentum below the Fermi momentum, where the spectral functions are well known. In this paper we extract a novel observable, the transparency ratio, Tp… ▽ More Nuclear transparency, Tp(A), is a measure of the average probability for a struck proton to escape the nucleus without significant re-interaction. Previously, nuclear transparencies were extructed for quasi-elastic A(e,e'p) knockout of protons with momentum below the Fermi momentum, where the spectral functions are well known. In this paper we extract a novel observable, the transparency ratio, Tp(A)/T_p(12C), for knockout of high-missing-momentum protons from the breakup of short range correlated pairs (2N-SRC) in Al, Fe and Pb nuclei relative to C. The ratios were measured at momentum transfer Q^2 > 1.5 (GeV/c)^2 and x_B > 1.2 where the reaction is expected to be dominated by electron scattering from 2N-SRC. The transparency ratios of the knocked-out protons coming from 2N-SRC breakup are 20 - 30% lower than those of previous results for low missing momentum. They agree with Glauber calculations and agree with renormalization of the previously published transparencies as proposed by recent theoretical investigations. The new transparencies scale as A^-1/3, which is consistent with dominance of scattering from nucleons at the nuclear surface. △ Less

Submitted 13 February, 2013; v1 submitted 21 December, 2012; originally announced December 2012.

Comments: 6 pages, 4 figures

Journal ref: Phys. Lett. B. 722, 63 (2013)

Virtual Compton Scattering and the Generalized Polarizabilities of the Proton at Q^2=0.92 and 1.76 GeV^2

Authors: H. Fonvieille, G. Laveissiere, N. Degrande, S. Jaminion, C. Jutier, L. Todor, R. Di Salvo, L. Van Hoorebeke, L. C. Alexa, B. D. Anderson, K. A. Aniol, K. Arundell, G. Audit, L. Auerbach, F. T. Baker, M. Baylac, J. Berthot, P. Y. Bertin, W. Bertozzi, L. Bimbot, W. U. Boeglin, E. J. Brash, V. Breton, H. Breuer, E. Burtin , et al. (139 additional authors not shown)

Abstract: Virtual Compton Scattering (VCS) on the proton has been studied at Jefferson Lab using the exclusive photon electroproduction reaction (e p --> e p gamma). This paper gives a detailed account of the analysis which has led to the determination of the structure functions P_LL-P_TT/epsilon and P_LT, and the electric and magnetic generalized polarizabilities (GPs) alpha_E(Q^2) and beta_M(Q^2) at value… ▽ More Virtual Compton Scattering (VCS) on the proton has been studied at Jefferson Lab using the exclusive photon electroproduction reaction (e p --> e p gamma). This paper gives a detailed account of the analysis which has led to the determination of the structure functions P_LL-P_TT/epsilon and P_LT, and the electric and magnetic generalized polarizabilities (GPs) alpha_E(Q^2) and beta_M(Q^2) at values of the four-momentum transfer squared Q^2= 0.92 and 1.76 GeV^2. These data, together with the results of VCS experiments at lower momenta, help building a coherent picture of the electric and magnetic GPs of the proton over the full measured Q^2-range, and point to their non-trivial behavior. △ Less

Submitted 28 June, 2012; v1 submitted 15 May, 2012; originally announced May 2012.

Comments: version 2: modified according to PRC Editor's and Referee's recommendations. Archival paper for the E93-050 experiment at JLab Hall A. 28 pages, 23 figures, 5 cross-section tables. To be submitted to Phys.Rev.C

Methods for Optical Calibration of the BigBite Hadron Spectrometer

Authors: M. Mihovilovic, K. Allada, B. D. Anderson, J. R. M. Annand, T. Averett, A. Camsonne, R. W. Chan, J. -P. Chen, K. Chirapatpimol, C. W. de Jager, S. Gilad, D. J. Hamilton, J. -O. Hansen, D. W. Higinbotham, J. Juang, X. Jiang, G. Jin, W. Korsch, J. J. LeRose, R. A. Lindgren, N. Liyanage, E. Long, R. Michaels, B. Moffit, P. Monaghan , et al. (17 additional authors not shown)

Abstract: The techniques for optical calibration of Jefferson Lab's large-acceptance magnetic hadron spectrometer, BigBite, have been examined. The most consistent and stable results were obtained by using a method based on singular value decomposition. In spite of the complexity of the optics, the particles' positions and momenta at the target have been precisely reconstructed from the coordinates measured… ▽ More The techniques for optical calibration of Jefferson Lab's large-acceptance magnetic hadron spectrometer, BigBite, have been examined. The most consistent and stable results were obtained by using a method based on singular value decomposition. In spite of the complexity of the optics, the particles' positions and momenta at the target have been precisely reconstructed from the coordinates measured in the detectors by means of a single back-tracing matrix. The technique is applicable to any similar magnetic spectrometer and any particle type. For 0.55 GeV/c protons, we have established the vertex resolution of 1.2 cm, angular resolutions of 7 mrad and 16 mrad (in-plane and out-of-plane, respectively), and a relative momentum resolution of 1.6%. △ Less

Submitted 19 April, 2012; v1 submitted 6 January, 2012; originally announced January 2012.

Comments: 26 pages, 13 figures

Journal ref: Nucl. Instrum. and Meth. 686 (2012) 20-30

Polarization components in $π^{0}$ photoproduction at photon energies up to 5.6 GeV

Authors: W. Luo, E. J. Brash, R. Gilman, M. K. Jones, M. Meziane, L. Pentchev, C. F. Perdrisat, A. J. R. Puckett, V. Punjabi, F. R. Wesselmann, A. Ahmidouch, I. Albayrak, K. A. Aniol, J. Arrington, A. Asaturyan, O. Ates, H. Baghdasaryan, F. Benmokhtar, W. Bertozzi, L. Bimbot, P. Bosted, W. Boeglin, C. Butuceanu, P. Carter, S. Chernenko , et al. (85 additional authors not shown)

Abstract: We present new data for the polarization observables of the final state proton in the $^{1}H(\vecγ,\vec{p})π^{0}$ reaction. These data can be used to test predictions based on hadron helicity conservation (HHC) and perturbative QCD (pQCD). These data have both small statistical and systematic uncertainties, and were obtained with beam energies between 1.8 and 5.6 GeV and for $π^{0}$ scattering ang… ▽ More We present new data for the polarization observables of the final state proton in the $^{1}H(\vecγ,\vec{p})π^{0}$ reaction. These data can be used to test predictions based on hadron helicity conservation (HHC) and perturbative QCD (pQCD). These data have both small statistical and systematic uncertainties, and were obtained with beam energies between 1.8 and 5.6 GeV and for $π^{0}$ scattering angles larger than 75$^{\circ}$ in center-of-mass (c.m.) frame. The data extend the polarization measurements data base for neutral pion photoproduction up to $E_γ=5.6 GeV$. The results show non-zero induced polarization above the resonance region. The polarization transfer components vary rapidly with the photon energy and $π^{0}$ scattering angle in c.m. frame. This indicates that HHC does not hold and that the pQCD limit is still not reached in the energy regime of this experiment. △ Less

Submitted 6 March, 2012; v1 submitted 21 September, 2011; originally announced September 2011.

Comments: 6 pages and 2 figures

Beam-Target Double Spin Asymmetry A_LT in Charged Pion Production from Deep Inelastic Scattering on a Transversely Polarized He-3 Target at 1.4<Q^2<2.7 GeV^2

Authors: J. Huang, K. Allada, C. Dutta, J. Katich, X. Qian, Y. Wang, Y. Zhang, K. Aniol, J. R. M. Annand, T. Averett, F. Benmokhtar, W. Bertozzi, P. C. Bradshaw, P. Bosted, A. Camsonne, M. Canan, G. D. Cates, C. Chen, J. -P. Chen, W. Chen, K. Chirapatpimol, E. Chudakov, E. Cisbani, J. C. Cornejo, F. Cusanno , et al. (90 additional authors not shown)

Abstract: We report the first measurement of the double-spin asymmetry $A_{LT}$ for charged pion electroproduction in semi\nobreakdash-inclusive deep\nobreakdash-inelastic electron scattering on a transversely polarized $^{3}$He target. The kinematics focused on the valence quark region, $0.16<x<0.35$ with $1.4<Q^{2}<2.7\,\textrm{GeV}^{2}$. The corresponding neutron $A_{LT}$ asymmetries were extracted from… ▽ More We report the first measurement of the double-spin asymmetry $A_{LT}$ for charged pion electroproduction in semi\nobreakdash-inclusive deep\nobreakdash-inelastic electron scattering on a transversely polarized $^{3}$He target. The kinematics focused on the valence quark region, $0.16<x<0.35$ with $1.4<Q^{2}<2.7\,\textrm{GeV}^{2}$. The corresponding neutron $A_{LT}$ asymmetries were extracted from the measured $^{3}$He asymmetries and proton over $^{3}$He cross section ratios using the effective polarization approximation. These new data probe the transverse momentum dependent parton distribution function $g_{1T}^{q}$ and therefore provide access to quark spin-orbit correlations. Our results indicate a positive azimuthal asymmetry for $π^{-}$ production on $^{3}$He and the neutron, while our $π^{+}$ asymmetries are consistent with zero. △ Less

Submitted 10 February, 2012; v1 submitted 2 August, 2011; originally announced August 2011.

Comments: 6 pages, 2 figures, 1 tables, published in PRL

Report number: JLAB-PHY-11-1359

Journal ref: Phys. Rev. Lett. 108, 052001 (2012)

Single Spin Asymmetries in Charged Pion Production from Semi-Inclusive Deep Inelastic Scattering on a Transversely Polarized $^3$He Target

Authors: X. Qian, K. Allada, C. Dutta, J. Huang, J. Katich, Y. Wang, Y. Zhang, K. Aniol, J. R. M. Annand, T. Averett, F. Benmokhtar, W. Bertozzi, P. C. Bradshaw, P. Bosted, A. Camsonne, M. Canan, G. D. Cates, C. Chen, J. -P. Chen, W. Chen, K. Chirapatpimol, E. Chudakov, E. Cisbani, J. C. Cornejo, F. Cusanno , et al. (90 additional authors not shown)

Abstract: We report the first measurement of target single spin asymmetries in the semi-inclusive $^3{He}(e,e'π^\pm)X$ reaction on a transversely polarized target. The experiment, conducted at Jefferson Lab using a 5.9 GeV electron beam, covers a range of 0.14 $< x <$ 0.34 with 1.3 $<Q^2<$ 2.7 GeV$^2$. The Collins and Sivers moments were extracted from the azimuthal angular dependence of the measured asymme… ▽ More We report the first measurement of target single spin asymmetries in the semi-inclusive $^3{He}(e,e'π^\pm)X$ reaction on a transversely polarized target. The experiment, conducted at Jefferson Lab using a 5.9 GeV electron beam, covers a range of 0.14 $< x <$ 0.34 with 1.3 $<Q^2<$ 2.7 GeV$^2$. The Collins and Sivers moments were extracted from the azimuthal angular dependence of the measured asymmetries. The extracted $π^\pm$ Collins moments for $^3$He are consistent with zero, except for the $π^+$ moment at $x=0.34$, which deviates from zero by 2.3$σ$. While the $π^-$ Sivers moments are consistent with zero, the $π^+$ Sivers moments favor negative values. The neutron results were extracted using the nucleon effective polarization and the measured cross section ratio of proton to $^3$He, and are largely consistent with the predictions of phenomenological fits and quark model calculations. △ Less

Submitted 16 August, 2011; v1 submitted 2 June, 2011; originally announced June 2011.

Comments: 6 pages, 2 figures, 2 tables, published in PRL

Journal ref: Phys.Rev.Lett.107:072003,2011

Final Analysis of Proton Form Factor Ratio Data at $\mathbf{Q^2 = 4.0}$, 4.8 and 5.6 GeV$\mathbf{^2}$

Authors: A. J. R. Puckett, E. J. Brash, O. Gayou, M. K. Jones, L. Pentchev, C. F. Perdrisat, V. Punjabi, K. A. Aniol, T. Averett, F. Benmokhtar, W. Bertozzi, L. Bimbot, J. R. Calarco, C. Cavata, Z. Chai, C. -C. Chang, T. Chang, J. P. Chen, E. Chudakov, R. De Leo, S. Dieterich, R. Endres, M. B. Epstein, S. Escoffier, K. G. Fissum. H. Fonvieille , et al. (49 additional authors not shown)

Abstract: Precise measurements of the proton electromagnetic form factor ratio $R = μ_p G_E^p/G_M^p$ using the polarization transfer method at Jefferson Lab have revolutionized the understanding of nucleon structure by revealing the strong decrease of $R$ with momentum transfer $Q^2$ for $Q^2 \gtrsim 1$ GeV$^2$, in strong disagreement with previous extractions of $R$ from cross section measurements. In part… ▽ More Precise measurements of the proton electromagnetic form factor ratio $R = μ_p G_E^p/G_M^p$ using the polarization transfer method at Jefferson Lab have revolutionized the understanding of nucleon structure by revealing the strong decrease of $R$ with momentum transfer $Q^2$ for $Q^2 \gtrsim 1$ GeV$^2$, in strong disagreement with previous extractions of $R$ from cross section measurements. In particular, the polarization transfer results have exposed the limits of applicability of the one-photon-exchange approximation and highlighted the role of quark orbital angular momentum in the nucleon structure. The GEp-II experiment in Jefferson Lab's Hall A measured $R$ at four $Q^2$ values in the range 3.5 GeV$^2 \le Q^2 \le 5.6$ GeV$^2$. A possible discrepancy between the originally published GEp-II results and more recent measurements at higher $Q^2$ motivated a new analysis of the GEp-II data. This article presents the final results of the GEp-II experiment, including details of the new analysis, an expanded description of the apparatus and an overview of theoretical progress since the original publication. The key result of the final analysis is a systematic increase in the results for $R$, improving the consistency of the polarization transfer data in the high-$Q^2$ region. This increase is the result of an improved selection of elastic events which largely removes the systematic effect of the inelastic contamination, underestimated by the original analysis. △ Less

Submitted 29 March, 2012; v1 submitted 28 February, 2011; originally announced February 2011.

Comments: 30 pages, 17 figures, 4 tables. Final version to appear in Phys. Rev. C

Journal ref: Phys. Rev. C 85:045203 (2012)

High Precision Measurement of the Proton Elastic Form Factor Ratio $μ_pG_E/G_M$ at low $Q^2$

Authors: X. Zhan, K. Allada, D. S. Armstrong, J. Arrington, W. Bertozzi, W. Boeglin, J. -P. Chen, K. Chirapatpimol, S. Choi, E. Chudakov, E. Cisbani, P. Decowski, C. Dutta, S. Frullani, E. Fuchey, F. Garibaldi, S. Gilad, R. Gilman, J. Glister, K. Hafidi, B. Hahn, J. -O. Hansen, D. W. Higinbotham, T. Holmstrom, R. J. Holt , et al. (46 additional authors not shown)

Abstract: We report a new, high-precision measurement of the proton elastic form factor ratio μ_p G_E/G_M for the four-momentum transfer squared Q^2 = 0.3-0.7 (GeV/c)^2. The measurement was performed at Jefferson Lab (JLab) in Hall A using recoil polarimetry. With a total uncertainty of approximately 1%, the new data clearly show that the deviation of the ratio μ_p G_E/G_M from unity observed in previous po… ▽ More We report a new, high-precision measurement of the proton elastic form factor ratio μ_p G_E/G_M for the four-momentum transfer squared Q^2 = 0.3-0.7 (GeV/c)^2. The measurement was performed at Jefferson Lab (JLab) in Hall A using recoil polarimetry. With a total uncertainty of approximately 1%, the new data clearly show that the deviation of the ratio μ_p G_E/G_M from unity observed in previous polarization measurements at high Q^2 continues down to the lowest Q^2 value of this measurement. The updated global fit that includes the new results yields an electric (magnetic) form factor roughly 2% smaller (1% larger) than the previous global fit in this Q^2 range. We obtain new extractions of the proton electric and magnetic radii, which are <r^2_E>^(1/2)=0.875+/-0.010 fm and <r^2_M>^(1/2)=0.867+/-0.020 fm. The charge radius is consistent with other recent extractions based on the electron-proton interaction, including the atomic hydrogen Lamb shift measurements, which suggests a missing correction in the comparison of measurements of the proton charge radius using electron probes and the recent extraction from the muonic hydrogen Lamb shift. △ Less

Submitted 31 August, 2011; v1 submitted 1 February, 2011; originally announced February 2011.

Comments: 12 pages, 3 figures

Journal ref: Phys. Lett. B 705 (2011) 59-64

Search for effects beyond the Born approximation in polarization transfer observables in $\vec{e}p$ elastic scattering

Authors: M. Meziane, E. J. Brash, R. Gilman, M. K. Jones, W. Luo, L. Pentchev, C. F. Perdrisat, A. J. R. Puckett, V. Punjabi, F. R. Wesselmann, A. Ahmidouch, I. Albayrak, K. A. Aniol, J. Arrington, A. Asaturyan, O. Ates, H. Baghdasaryan, F. Benmokhtar, W. Bertozzi, L. Bimbot, P. Bosted, W. Boeglin, C. Butuceanu, P. Carter, S. Chernenko , et al. (86 additional authors not shown)

Abstract: Intensive theoretical and experimental efforts over the past decade have aimed at explaining the discrepancy between data for the proton electric to magnetic form factor ratio, $G_{E}/G_{M}$, obtained separately from cross section and polarization transfer measurements. One possible explanation for this difference is a two-photon-exchange (TPEX) contribution. In an effort to search for effects bey… ▽ More Intensive theoretical and experimental efforts over the past decade have aimed at explaining the discrepancy between data for the proton electric to magnetic form factor ratio, $G_{E}/G_{M}$, obtained separately from cross section and polarization transfer measurements. One possible explanation for this difference is a two-photon-exchange (TPEX) contribution. In an effort to search for effects beyond the one-photon-exchange or Born approximation, we report measurements of polarization transfer observables in the elastic $H(\vec{e},e'\vec{p})$ reaction for three different beam energies at a fixed squared momentum transfer $Q^2 = 2.5$ GeV$^2$, spanning a wide range of the virtual photon polarization parameter, $ε$. From these measured polarization observables, we have obtained separately the ratio $R$, which equals $μ_p G_{E}/G_{M}$ in the Born approximation, and the longitudinal polarization transfer component $P_\ell$, with statistical and systematic uncertainties of $ΔR \approx \pm 0.01 \mbox{(stat)} \pm 0.013 \mbox{(syst)}$ and $ΔP_\ell/P^{Born}_{\ell} \approx \pm 0.006 \mbox{(stat)}\pm 0.01 \mbox{(syst)}$. The ratio $R$ is found to be independent of $ε$ at the 1.5% level, while the $ε$ dependence of $P_\ell$ shows an enhancement of $(2.3 \pm 0.6) %$ relative to the Born approximation at large $ε$. △ Less

Submitted 28 February, 2011; v1 submitted 1 December, 2010; originally announced December 2010.

Journal ref: Phys.Rev.Lett.106:132501,2011

Recoil Polarization Measurements of the Proton Electromagnetic Form Factor Ratio to Q^2 = 8.5 GeV^2

Authors: A. J. R. Puckett, E. J. Brash, M. K. Jones, W. Luo, M. Meziane, L. Pentchev, C. F. Perdrisat, V. Punjabi, F. R. Wesselmann, A. Ahmidouch, I. Albayrak, K. A. Aniol, J. Arrington, A. Asaturyan, H. Baghdasaryan, F. Benmokhtar, W. Bertozzi, L. Bimbot, P. Bosted, W. Boeglin, C. Butuceanu, P. Carter, S. Chernenko, E. Christy, M. Commisso , et al. (81 additional authors not shown)

Abstract: Among the most fundamental observables of nucleon structure, electromagnetic form factors are a crucial benchmark for modern calculations describing the strong interaction dynamics of the nucleon's quark constituents; indeed, recent proton data have attracted intense theoretical interest. In this letter, we report new measurements of the proton electromagnetic form factor ratio using the recoil po… ▽ More Among the most fundamental observables of nucleon structure, electromagnetic form factors are a crucial benchmark for modern calculations describing the strong interaction dynamics of the nucleon's quark constituents; indeed, recent proton data have attracted intense theoretical interest. In this letter, we report new measurements of the proton electromagnetic form factor ratio using the recoil polarization method, at momentum transfers Q2=5.2, 6.7, and 8.5 GeV2. By extending the range of Q2 for which GEp is accurately determined by more than 50%, these measurements will provide significant constraints on models of nucleon structure in the non-perturbative regime. △ Less

Submitted 28 May, 2010; v1 submitted 19 May, 2010; originally announced May 2010.

Journal ref: Phys.Rev.Lett.104:242301,2010

The Role of Mesons in the Electromagnetic Form Factors of the Nucleon

Authors: C. Crawford, T. Akdogan, R. Alarcon, W. Bertozzi, E. Booth, T. Botto, J. R. Calarco, B. Clasie, A. DeGrush, T. W. Donnelly, K. Dow, M. Farkhondeh, R. Fatemi, O. Filoti, W. Franklin, H. Gao, E. Geis, S. Gilad, D. Hasell, P. Karpius, M. Kohl, H. Kolster, T. Lee, E. Lomon, A. Maschinot , et al. (22 additional authors not shown)

Abstract: The roles played by mesons in the electromagnetic form factors of the nucleon are explored using as a basis a model containing vector mesons with coupling to the continuum together with the asymptotic $Q^2$ behavior of perturbative QCD. Specifically, the vector dominance model (GKex) developed by Lomon is employed, as it is known to be very successful in representing the existing high-quality data… ▽ More The roles played by mesons in the electromagnetic form factors of the nucleon are explored using as a basis a model containing vector mesons with coupling to the continuum together with the asymptotic $Q^2$ behavior of perturbative QCD. Specifically, the vector dominance model (GKex) developed by Lomon is employed, as it is known to be very successful in representing the existing high-quality data published to date. An analysis is made of the experimental uncertainties present when the differences between the GKex model and the data are expanded in orthonormal basis functions. A main motivation for the present study is to provide insight into how the various ingredients in this model yield the measured behavior, including discussions of when dipole form factors are to be expected or not, of which mesons are the major contributors, for instance, at low-$Q^2$ or large distances, and of what effects are predicted from coupling to the continuum. Such insights are first discussed in momentum space, followed by an analysis of how different and potentially useful information emerges when both the experimental and theoretical electric form factors are Fourier transformed to coordinate space. While these Fourier transforms should not be interpreted as "charge distributions", nevertheless the roles played by the various mesons, especially which are dominant at large or small distance scales, can be explored via such experiment--theory comparisons. △ Less

Submitted 1 August, 2010; v1 submitted 3 March, 2010; originally announced March 2010.

Comments: Resubmitted to PRC

Probing Cold Dense Nuclear Matter

Authors: R. Subedi, R. Shneor, P. Monaghan, B. D. Anderson, K. Aniol, J. Annand, J. Arrington, H. Benaoum, F. Benmokhtar, W. Bertozzi, W. Boeglin, J. -P. Chen, Seonho Choi, E. Cisbani, B. Craver, S. Frullani, F. Garibaldi, S. Gilad, R. Gilman, O. Glamazdin, J. -O. Hansen, D. W. Higinbotham, T. Holmstrom, H. Ibrahim, R. Igarashi , et al. (40 additional authors not shown)

Abstract: The protons and neutrons in a nucleus can form strongly correlated nucleon pairs. Scattering experiments, where a proton is knocked-out of the nucleus with high momentum transfer and high missing momentum, show that in 12C the neutron-proton pairs are nearly twenty times as prevalent as proton-proton pairs and, by inference, neutron-neutron pairs. This difference between the types of pairs is du… ▽ More The protons and neutrons in a nucleus can form strongly correlated nucleon pairs. Scattering experiments, where a proton is knocked-out of the nucleus with high momentum transfer and high missing momentum, show that in 12C the neutron-proton pairs are nearly twenty times as prevalent as proton-proton pairs and, by inference, neutron-neutron pairs. This difference between the types of pairs is due to the nature of the strong force and has implications for understanding cold dense nuclear systems such as neutron stars. △ Less

Submitted 11 August, 2009; originally announced August 2009.

Comments: 12 pages, 5 figures

Report number: JLAB-PHY-08-828

Journal ref: Science 320:1476-1478,2008

The Charge Form Factor of the Neutron at Low Momentum Transfer from the $^{2}\vec{\rm H}(\vec{\rm e},{\rm e}'{\rm n}){\rm p}$ Reaction

Authors: E. Geis, V. Ziskin, T. Akdogan, H. Arenhoevel, R. Alarcon, W. Bertozzi, E. Booth, T. Botto, J. Calarco, B. Clasie, C. B. Crawford, A. DeGrush, T. W. Donnelly, K. Dow, M. Farkhondeh, R. Fatemi, O. Filoti, W. Franklin, H. Gao, S. Gilad, D. Hasell, P. Karpius, M. Kohl, H. Kolster, T. Lee , et al. (23 additional authors not shown)

Abstract: We report new measurements of the neutron charge form factor at low momentum transfer using quasielastic electrodisintegration of the deuteron. Longitudinally polarized electrons at an energy of 850 MeV were scattered from an isotopically pure, highly polarized deuterium gas target. The scattered electrons and coincident neutrons were measured by the Bates Large Acceptance Spectrometer Toroid (B… ▽ More We report new measurements of the neutron charge form factor at low momentum transfer using quasielastic electrodisintegration of the deuteron. Longitudinally polarized electrons at an energy of 850 MeV were scattered from an isotopically pure, highly polarized deuterium gas target. The scattered electrons and coincident neutrons were measured by the Bates Large Acceptance Spectrometer Toroid (BLAST) detector. The neutron form factor ratio $G^{n}_{E}/G^{n}_{M}$ was extracted from the beam-target vector asymmetry $A_{ed}^{V}$ at four-momentum transfers $Q^{2}=0.14$, 0.20, 0.29 and 0.42 (GeV/c)$^{2}$. △ Less

Submitted 8 April, 2008; v1 submitted 26 March, 2008; originally announced March 2008.

Comments: 5 pages, 3 figures, submitted to Phys. Rev. Lett

Journal ref: Phys.Rev.Lett.101:042501,2008