Showing 1–41 of 41 results for author: Zhan, X

Deeply virtual Compton scattering off the neutron

Authors: M. Benali, C. Desnault, M. Mazouz, Z. Ahmed, H. Albataineh, K. Allada, K. A. Aniol, V. Bellini, W. Boeglin, P. Bertin, M. Brossard, A. Camsonne, M. Canan, S. Chandavar, C. Chen, J. -P. Chen, M. Defurne, C. W. de Jager, R. de Leo, A. Deur, L. El Fassi, R. Ent, D. Flay, M. Friend, E. Fuchey , et al. (74 additional authors not shown)

Abstract: The three-dimensional structure of nucleons (protons and neutrons) is embedded in so-called generalized parton distributions, which are accessible from deeply virtual Compton scattering. In this process, a high energy electron is scattered off a nucleon by exchanging a virtual photon. Then, a highly-energetic real photon is emitted from one of the quarks inside the nucleon, which carries informati… ▽ More The three-dimensional structure of nucleons (protons and neutrons) is embedded in so-called generalized parton distributions, which are accessible from deeply virtual Compton scattering. In this process, a high energy electron is scattered off a nucleon by exchanging a virtual photon. Then, a highly-energetic real photon is emitted from one of the quarks inside the nucleon, which carries information on the quark's transverse position and longitudinal momentum. By measuring the cross-section of deeply virtual Compton scattering, Compton form factors related to the generalized parton distributions can be extracted. Here, we report the observation of unpolarized deeply virtual Compton scattering off a deuterium target. From the measured photon-electroproduction cross-sections, we have extracted the cross-section of a quasi-free neutron and a coherent deuteron. Due to the approximate isospin symmetry of quantum chromodynamics, we can determine the contributions from the different quark flavours to the helicity-conserved Compton form factors by combining our measurements with previous ones probing the proton's internal structure. These results advance our understanding of the description of the nucleon structure, which is important to solve the proton spin puzzle. △ Less

Submitted 5 September, 2021; originally announced September 2021.

Journal ref: Nature Physics 16 (2020) 191-198

Measurement of the generalized spin polarizabilities of the neutron in the low $Q^2$ region

Authors: V. Sulkosky, C. Peng, J. -P. Chen, A. Deur, S. Abrahamyan, K. A. Aniol, D. S. Armstrong, T. Averett, S. L. Bailey, A. Beck, P. Bertin, F. Butaru, W. Boeglin, A. Camsonne, G. D. Cates, C. C. Chang, Seonho Choi, E. Chudakov, L. Coman, J. C Cornejo, B. Craver, F. Cusanno, R. De Leo, C. W. de Jager, J. D. Denton , et al. (84 additional authors not shown)

Abstract: Understanding the nucleon spin structure in the regime where the strong interaction becomes truly strong poses a challenge to both experiment and theory. At energy scales below the nucleon mass of about 1 GeV, the intense interaction among the quarks and gluons inside the nucleon makes them highly correlated. Their coherent behaviour causes the emergence of effective degrees of freedom, requiring… ▽ More Understanding the nucleon spin structure in the regime where the strong interaction becomes truly strong poses a challenge to both experiment and theory. At energy scales below the nucleon mass of about 1 GeV, the intense interaction among the quarks and gluons inside the nucleon makes them highly correlated. Their coherent behaviour causes the emergence of effective degrees of freedom, requiring the application of non-perturbative techniques, such as chiral effective field theory. Here, we present measurements of the neutron's generalized spin-polarizabilities that quantify the neutron's spin precession under electromagnetic fields at very low energy-momentum transfer squared down to 0.035 GeV$^2$. In this regime, chiral effective field theory calculations are expected to be applicable. Our data, however, show a strong discrepancy with these predictions, presenting a challenge to the current description of the neutron's spin properties. △ Less

Submitted 23 February, 2022; v1 submitted 4 March, 2021; originally announced March 2021.

Comments: V1: initial version submitted to Nature Physics. V2: Published version. 16 pages, 7 figures. Additional material: 4 data tables (18 pages) V3: Typo corrected in author list. Paper content unchanged

Report number: JLAB-PHY-21-3312, DOE/OR/23177-5119

Journal ref: Nature Physics, Vol. 17 687-692 (2021)

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)

Measurement of the 3He Spin-Structure Functions and of Neutron (3He) Spin-Dependent Sum Rules at 0.035<Q^2<0.24 GeV^2

Authors: V. Sulkosky, J. T. Singh, C. Peng, J. -P. Chen, A. Deur, S. Abrahamyan, K. A. Aniol, D. S. Armstrong, T. Averett, S. L. Bailey, A. Beck, P. Bertin, F. Butaru, W. Boeglin, A. Camsonne, G. D. Cates, C. C. Chang, Seonho Choi, E. Chudakov, L. Coman, J. C Cornejo, B. Craver, F. Cusanno, R. De Leo, C. W. de Jager , et al. (84 additional authors not shown)

Abstract: The spin-structure functions $g_1$ and $g_2$, and the spin-dependent partial cross-section $σ_\mathrm{TT}$ have been extracted from the polarized cross-sections differences, $Δσ_{\parallel}\hspace{-0.06cm}\left(ν,Q^{2}\right)$ and $Δσ_{\perp}\hspace{-0.06cm}\left(ν,Q^{2}\right)$ measured for the $\vec{^\textrm{3}\textrm{He}}(\vec{\textrm{e}},\textrm{e}')\textrm{X}$ reaction, in the E97-110 experim… ▽ More The spin-structure functions $g_1$ and $g_2$, and the spin-dependent partial cross-section $σ_\mathrm{TT}$ have been extracted from the polarized cross-sections differences, $Δσ_{\parallel}\hspace{-0.06cm}\left(ν,Q^{2}\right)$ and $Δσ_{\perp}\hspace{-0.06cm}\left(ν,Q^{2}\right)$ measured for the $\vec{^\textrm{3}\textrm{He}}(\vec{\textrm{e}},\textrm{e}')\textrm{X}$ reaction, in the E97-110 experiment at Jefferson Lab. Polarized electrons with energies from 1.147 to 4.404 GeV were scattered at angles of 6$^{\circ}$ and 9$^{\circ}$ from a longitudinally or transversely polarized $^{3}$He target. The data cover the kinematic regions of the quasi-elastic, resonance production and beyond. From the extracted spin-structure functions, the first moments $\overline{Γ_1}\hspace{-0.06cm}\left(Q^{2}\right)$, $Γ_2\hspace{-0.06cm}\left(Q^{2}\right)$ and $I_{\mathrm{TT}}\hspace{-0.06cm}\left(Q^{2}\right)$ are evaluated with high precision for the neutron in the $Q^2$ range from 0.035 to 0.24~GeV$^{2}$. The comparison of the data and the chiral effective field theory predictions reveals the importance of proper treatment of the $Δ$ degree of freedom for spin observables. △ Less

Submitted 23 April, 2020; v1 submitted 15 August, 2019; originally announced August 2019.

Comments: 7 pages, 5 figures, 3 tables. Version published in Phys. Lett. B

Report number: JLAB-PHY-19-3015

Journal ref: Phys.Lett.B 805 135428 (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

Dispersive Corrections to the Born Approximation in Elastic Electron-Nucleus Scattering in the Intermediate Energy Regime

Authors: P. Gueye, A. A. Kabir J. Glister, B. W. Lee, R. Gilman, D. W. Higinbotham, E. Piasetzky, G. Ron, A. J. Sarty, S. Strauch, A. Adeyemi, K. Allada, W. Armstrong, J. Arrington, H. Arenhovel, A. Beck, F. Benmokhtar, B. L. Berman, W. Boeglin, E. Brash, A. Camsonne, J. Calarco, J. P. Chen, S. Choi, E. Chudakov, L. Coman , et al. (67 additional authors not shown)

Abstract: Measurements of elastic electron scattering data within the past decade have highlighted two-photon exchange contributions as a necessary ingredient in theoretical calculations to precisely evaluate hydrogen elastic scattering cross sections. This correction can modify the cross section at the few percent level. In contrast, dispersive effects can cause significantly larger changes from the Born a… ▽ More Measurements of elastic electron scattering data within the past decade have highlighted two-photon exchange contributions as a necessary ingredient in theoretical calculations to precisely evaluate hydrogen elastic scattering cross sections. This correction can modify the cross section at the few percent level. In contrast, dispersive effects can cause significantly larger changes from the Born approximation. The purpose of this experiment is to extract the carbon-12 elastic cross section around the first diffraction minimum, where the Born term contributions to the cross section are small to maximize the sensitivity to dispersive effects. The analysis uses the LEDEX data from the high resolution Jefferson Lab Hall A spectrometers to extract the cross sections near the first diffraction minimum of 12C at beam energies of 362 MeV and 685 MeV. The results are in very good agreement with previous world data, although with less precision. The average deviation from a static nuclear charge distribution expected from linear and quadratic fits indicate a 30.6% contribution of dispersive effects to the cross section at 1 GeV. The magnitude of the dispersive effects near the first diffraction minimum of 12C has been confirmed to be large with a strong energy dependence and could account for a large fraction of the magnitude for the observed quenching of the longitudinal nuclear response. These effects could also be important for nuclei radii extracted from parity-violating asymmetries measured near a diffraction minimum. △ Less

Submitted 30 March, 2020; v1 submitted 31 May, 2018; originally announced May 2018.

Comments: 14 pages, 10 figures

Report number: JLAB-PHY-18-2707

Journal ref: Eur. Phys. J. A 56 (2020) 126

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)

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)

A Glimpse of Gluons through Deeply Virtual Compton Scattering on the Proton

Authors: M. Defurne, A. Martì Jiménez-Argüello, Z. Ahmed, H. Albataineh, K. Allada, K. A. Aniol, V. Bellini, M. Benali, W. Boeglin, P. Bertin, M. Brossard, A. Camsonne, M. Canan, S. Chandavar, C. Chen, J. -P. Chen, C. W. de Jager, R. de Leo, C. Desnault, A. Deur, L. El Fassi, R. Ent, D. Flay, M. Friend, E. Fuchey , et al. (69 additional authors not shown)

Abstract: The proton is composed of quarks and gluons, bound by the most elusive mechanism of strong interaction called confinement. In this work, the dynamics of quarks and gluons are investigated using deeply virtual Compton scattering (DVCS): produced by a multi-GeV electron, a highly virtual photon scatters off the proton which subsequently radiates a high energy photon. Similarly to holography, measuri… ▽ More The proton is composed of quarks and gluons, bound by the most elusive mechanism of strong interaction called confinement. In this work, the dynamics of quarks and gluons are investigated using deeply virtual Compton scattering (DVCS): produced by a multi-GeV electron, a highly virtual photon scatters off the proton which subsequently radiates a high energy photon. Similarly to holography, measuring not only the magnitude but also the phase of the DVCS amplitude allows to perform 3D images of the internal structure of the proton. The phase is made accessible through the quantum-mechanical interference of DVCS with the Bethe-Heitler (BH) process, in which the final photon is emitted by the electron rather than the proton. We report herein the first full determination of the BH-DVCS interference by exploiting the distinct energy dependences of the DVCS and BH amplitudes. In the high energy regime where the scattering process is expected to occur off a single quark in the proton, these accurate measurements show an intriguing sensitivity to gluons, the carriers of the strong interaction. △ Less

Submitted 28 March, 2017; originally announced March 2017.

Rosenbluth separation of the $π^0$ Electroproduction Cross Section off the Neutron

Authors: M. Mazouz, Z. Ahmed, H. Albataineh, K. Allada, K. A. Aniol, V. Bellini, M. Benali, W. Boeglin, P. Bertin, M. Brossard, A. Camsonne, M. Canan, S. Chandavar, C. Chen, J. -P. Chen, M. Defurne, C. W. de Jager, R. de Leo, C. Desnault, A. Deur, L. El Fassi, R. Ent, D. Flay, M. Friend, E. Fuchey , et al. (73 additional authors not shown)

Abstract: We report the first longitudinal/transverse separation of the deeply virtual exclusive $π^0$ electroproduction cross section off the neutron and coherent deuteron. The corresponding four structure functions $dσ_L/dt$, $dσ_T/dt$, $dσ_{LT}/dt$ and $dσ_{TT}/dt$ are extracted as a function of the momentum transfer to the recoil system at $Q^2$=1.75 GeV$^2$ and $x_B$=0.36. The $ed \to edπ^0$ cross sect… ▽ More We report the first longitudinal/transverse separation of the deeply virtual exclusive $π^0$ electroproduction cross section off the neutron and coherent deuteron. The corresponding four structure functions $dσ_L/dt$, $dσ_T/dt$, $dσ_{LT}/dt$ and $dσ_{TT}/dt$ are extracted as a function of the momentum transfer to the recoil system at $Q^2$=1.75 GeV$^2$ and $x_B$=0.36. The $ed \to edπ^0$ cross sections are found compatible with the small values expected from theoretical models. The $en \to enπ^0$ cross sections show a dominance from the response to transversely polarized photons, and are in good agreement with calculations based on the transversity GPDs of the nucleon. By combining these results with previous measurements of $π^0$ electroproduction off the proton, we present a flavor decomposition of the $u$ and $d$ quark contributions to the cross section. △ Less

Submitted 2 February, 2017; originally announced February 2017.

Comments: 6 pages, 6 figures, Submitted to Phys. Rev. Lett

Journal ref: Phys. Rev. Lett. 118, 222002 (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)

Rosenbluth separation of the $π^0$ electroproduction cross section

Authors: M. Defurne, M. Mazouz, H. Albataineh, K. Allada, K. A. Aniol, V. Bellini, M. Benali, W. Boeglin, P. Bertin, M. Brossard, A. Camsonne, M. Canan, S. Chandavar, C. Chen, J. -P. Chen, C. W. de Jager, R. de Leo, C. Desnault, A. Deur, L. El Fassi, R. Ent, D. Flay, M. Friend, E. Fuchey, S. Frullani , et al. (69 additional authors not shown)

Abstract: We present deeply virtual $π^0$ electroproduction cross-section measurements at $x_B$=0.36 and three different $Q^2$--values ranging from 1.5 to 2 GeV$^2$, obtained from experiment E07-007 that ran in the Hall A at Jefferson Lab. The Rosenbluth technique was used to separate the longitudinal and transverse responses. Results demonstrate that the cross section is dominated by its transverse compone… ▽ More We present deeply virtual $π^0$ electroproduction cross-section measurements at $x_B$=0.36 and three different $Q^2$--values ranging from 1.5 to 2 GeV$^2$, obtained from experiment E07-007 that ran in the Hall A at Jefferson Lab. The Rosenbluth technique was used to separate the longitudinal and transverse responses. Results demonstrate that the cross section is dominated by its transverse component, and thus is far from the asymptotic limit predicted by perturbative Quantum Chromodynamics. An indication of a non-zero longitudinal contribution is provided by the interference term $σ_{LT}$ also measured. Results are compared with several models based on the leading twist approach of Generalized Parton Distributions (GPDs). In particular, a fair agreement is obtained with models where the scattering amplitude is described by a convolution of chiral-odd (transversity) GPDs of the nucleon with the twist-3 pion distribution amplitude. Therefore, neutral pion electroproduction may offer the exciting possibility of accessing transversity GPDs through experiment. △ Less

Submitted 2 August, 2016; originally announced August 2016.

Comments: Submitted to Physical Review Letters

Journal ref: Phys. Rev. Lett. 117, 262001 (2016)

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)

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)

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)

Hard Two-body Photodisintegration of 3He

Authors: I. Pomerantz, Y. Ilieva, R. Gilman, D. W. Higinbotham, E. Piasetzky, S. Strauch, K. P. Adhikari, M. Aghasyan, K. Allada, M. J. Amaryan, S. Anefalos Pereira, M. Anghinolfi, H. Baghdasaryan, J. Ball, N. A. Baltzell, M. Battaglieri, V. Batourine, A. Beck, S. Beck, I. Bedlinskiy, B. L. Berman, A. S. Biselli, W. Boeglin, J. Bono, C. Bookwalter , et al. (175 additional authors not shown)

Abstract: We have measured cross sections for the gamma+3He->p+d reaction at photon energies of 0.4 - 1.4 GeV and a center-of-mass angle of 90 deg. We observe dimensional scaling above 0.7 GeV at this center-of-mass angle. This is the first observation of dimensional scaling in the photodisintegration of a nucleus heavier than the deuteron. We have measured cross sections for the gamma+3He->p+d reaction at photon energies of 0.4 - 1.4 GeV and a center-of-mass angle of 90 deg. We observe dimensional scaling above 0.7 GeV at this center-of-mass angle. This is the first observation of dimensional scaling in the photodisintegration of a nucleus heavier than the deuteron. △ Less

Submitted 20 March, 2013; originally announced March 2013.

Report number: JLAB-PHY-13-1728

New Measurements of the Transverse Beam Asymmetry for Elastic Electron Scattering from Selected Nuclei

Authors: The HAPPEX, PREX Collaborations, :, S. Abrahamyan, A. Acha, A. Afanasev, Z. Ahmed, H. Albataineh, K. Aniol, D. S. Armstrong, W. Armstrong, J. Arrington, T. Averett, B. Babineau, S. L. Bailey, J. Barber, A. Barbieri, A. Beck, V. Bellini, R. Beminiwattha, H. Benaoum, J. Benesch, F. Benmokhtar, P. Bertin, T. Bielarski , et al. (173 additional authors not shown)

Abstract: We have measured the beam-normal single-spin asymmetry $A_n$ in the elastic scattering of 1-3 GeV transversely polarized electrons from $^1$H and for the first time from $^4$He, $^{12}$C, and $^{208}$Pb. For $^1$H, $^4$He and $^{12}$C, the measurements are in agreement with calculations that relate $A_n$ to the imaginary part of the two-photon exchange amplitude including inelastic intermediate st… ▽ More We have measured the beam-normal single-spin asymmetry $A_n$ in the elastic scattering of 1-3 GeV transversely polarized electrons from $^1$H and for the first time from $^4$He, $^{12}$C, and $^{208}$Pb. For $^1$H, $^4$He and $^{12}$C, the measurements are in agreement with calculations that relate $A_n$ to the imaginary part of the two-photon exchange amplitude including inelastic intermediate states. Surprisingly, the $^{208}$Pb result is significantly smaller than the corresponding prediction using the same formalism. These results suggest that a systematic set of new $A_n$ measurements might emerge as a new and sensitive probe of the structure of heavy nuclei. △ Less

Submitted 12 October, 2012; v1 submitted 30 August, 2012; originally announced August 2012.

Comments: 5 pages, 3 figures, accepted by PRL. v3: fixed one author name and affiliation, otherwise no change

Journal ref: Phys. Rev. Lett. 109, (2012) 192501

Measurement of the Neutron Radius of 208Pb Through Parity-Violation in Electron Scattering

Authors: S. Abrahamyan, Z. Ahmed, H. Albataineh, K. Aniol, D. S. Armstrong, W. Armstrong, T. Averett, B. Babineau, A. Barbieri, V. Bellini, R. Beminiwattha, J. Benesch, F. Benmokhtar, T. Bielarski, W. Boeglin, A. Camsonne, M. Canan, P. Carter, G. D. Cates, C. Chen, J. -P. Chen, O. Hen, F. Cusanno, M. M. Dalton, R. De Leo , et al. (110 additional authors not shown)

Abstract: We report the first measurement of the parity-violating asymmetry A_PV in the elastic scattering of polarized electrons from 208Pb. A_PV is sensitive to the radius of the neutron distribution (Rn). The result A_PV = 0.656 \pm 0.060 (stat) \pm 0.014 (syst) ppm corresponds to a difference between the radii of the neutron and proton distributions Rn - Rp = 0.33 +0.16 -0.18 fm and provides the first e… ▽ More We report the first measurement of the parity-violating asymmetry A_PV in the elastic scattering of polarized electrons from 208Pb. A_PV is sensitive to the radius of the neutron distribution (Rn). The result A_PV = 0.656 \pm 0.060 (stat) \pm 0.014 (syst) ppm corresponds to a difference between the radii of the neutron and proton distributions Rn - Rp = 0.33 +0.16 -0.18 fm and provides the first electroweak observation of the neutron skin which is expected in a heavy, neutron-rich nucleus. △ Less

Submitted 13 January, 2012; v1 submitted 12 January, 2012; originally announced January 2012.

Comments: 6 pages, 1 figure

Report number: JLAB-PHY-12-1480

Journal ref: Phys. Rev. Lett. 108, 112502 (2012)

High Precision Measurement of the Proton Elastic Form Factor Ratio at Low $Q^2$

Authors: Xiaohui Zhan

Abstract: Jefferson Lab experiment E08-007 measured the proton elastic form factor ratio $μ_pG_E/G_M$ in the range of $Q^2=0.3-0.7(\mathrm{GeV}/c)^2$ by recoil polarimetry. Data were taken in 2008 at the Thomas Jefferson National Accelerator Facility in Virginia, USA. A 1.2 GeV polarized electron beam was scattered off a cryogenic hydrogen target. The recoil proton was detected in the left HRS in coincidenc… ▽ More Jefferson Lab experiment E08-007 measured the proton elastic form factor ratio $μ_pG_E/G_M$ in the range of $Q^2=0.3-0.7(\mathrm{GeV}/c)^2$ by recoil polarimetry. Data were taken in 2008 at the Thomas Jefferson National Accelerator Facility in Virginia, USA. A 1.2 GeV polarized electron beam was scattered off a cryogenic hydrogen target. The recoil proton was detected in the left HRS in coincidence with the elasticly scattered electrons tagged by the BigBite spectrometer. The proton polarization was measured by the focal plane polarimeter (FPP). In this low $Q^2$ region, previous measurement from Jefferson Lab Hall A (LEDEX) along with various fits and calculations indicate substantial deviations of the ratio from unity. For this new measurement, the proposed statistical uncertainty ($<1%$) was achieved. These new results are a few percent lower than expected from previous world data and fits, which indicate a smaller $G_{Ep}$ at this region. Beyond the intrinsic interest in nucleon structure, the new results also have implications in determining the proton Zemach radius and the strangeness form factors from parity violation experiments. △ Less

Submitted 24 August, 2011; v1 submitted 22 August, 2011; originally announced August 2011.

Comments: PhD Thesis, Massachusetts Institute of Technology, 2010

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)

New Precision Limit on the Strange Vector Form Factors of the Proton

Authors: HAPPEX collaboration, Z. Ahmed, K. Allada, K. A. Aniol, D. S. Armstrong, J. Arrington, P. Baturin, V. Bellini, J. Benesch, R. Beminiwattha, F. Benmokhtar, M. Canan, A. Camsonne, G. D. Cates, J. -P. Chen, E. Chudakov, E. Cisbani, M. M. Dalton, C. W. de Jager, R. De Leo, W. Deconinck, P. Decowski, X. Deng, A. Deur, C. Dutta , et al. (80 additional authors not shown)

Abstract: The parity-violating cross-section asymmetry in the elastic scattering of polarized electrons from unpolarized protons has been measured at a four-momentum transfer squared Q2 = 0.624 GeV and beam energy E =3.48 GeV to be A_PV = -23.80 +/- 0.78 (stat) +/- 0.36 (syst) parts per million. This result is consistent with zero contribution of strange quarks to the combination of electric and magnetic fo… ▽ More The parity-violating cross-section asymmetry in the elastic scattering of polarized electrons from unpolarized protons has been measured at a four-momentum transfer squared Q2 = 0.624 GeV and beam energy E =3.48 GeV to be A_PV = -23.80 +/- 0.78 (stat) +/- 0.36 (syst) parts per million. This result is consistent with zero contribution of strange quarks to the combination of electric and magnetic form factors G_E^s + 0.517 G_M^s = 0.003 +/- 0.010 (stat) +/- 0.004 (syst) +/- 0.009 (ff), where the third error is due to the limits of precision on the electromagnetic form factors and radiative corrections. With this measurement, the world data on strange contributions to nucleon form factors are seen to be consistent with zero and not more than a few percent of the proton form factors. △ Less

Submitted 5 July, 2011; originally announced July 2011.

Comments: 5 pages, 3 figures

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

Low Q^2 measurements of the proton form factor ratio $mu_p G_E / G_M$

Authors: G. Ron, X. Zhan, J. Glister, B. Lee, K. Allada, W. Armstrong, J. Arrington, A. Beck, F. Benmokhtar, B. L. Berman, W. Boeglin, E. Brash, A. Camsonne, J. Calarco, J. P. Chen, S. Choi, E. Chudakov, L. Coman, B. Craver, F. Cusanno, J. Dumas, C. Dutta, R. Feuerbach, A. Freyberger, S. Frullani , et al. (62 additional authors not shown)

Abstract: We present an updated extraction of the proton electromagnetic form factor ratio, mu_p G_E/G_M, at low Q^2. The form factors are sensitive to the spatial distribution of the proton, and precise measurements can be used to constrain models of the proton. An improved selection of the elastic events and reduced background contributions yielded a small systematic reduction in the ratio mu_p G_E/G_M co… ▽ More We present an updated extraction of the proton electromagnetic form factor ratio, mu_p G_E/G_M, at low Q^2. The form factors are sensitive to the spatial distribution of the proton, and precise measurements can be used to constrain models of the proton. An improved selection of the elastic events and reduced background contributions yielded a small systematic reduction in the ratio mu_p G_E/G_M compared to the original analysis. △ Less

Submitted 30 August, 2011; v1 submitted 29 March, 2011; originally announced March 2011.

Comments: 12 pages, 5 figures, archival paper for proton form factor extraction from Jefferson Lab "LEDEX" experiment

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

Transverse Momentum Dependent Parton Distribution/Fragmentation Functions at an Electron-Ion Collider

Authors: M. Anselmino, H. Avakian, D. Boer, F. Bradamante, M. Burkardt, J. P. Chen, E. Cisbani, M. Contalbrigo, D. Crabb, D. Dutta, L. Gamberg, H. Gao, D. Hasch, J. Huang, M. Huang, Z. Kang, C. Keppel, G. Laskaris, Z-T. Liang, M. X. Liu, N. Makins, R. D. Mckeown, A. Metz, Z-E. Meziani, B. Musch , et al. (18 additional authors not shown)

Abstract: We present a summary of a recent workshop held at Duke University on Partonic Transverse Momentum in Hadrons: Quark Spin-Orbit Correlations and Quark-Gluon Interactions. The transverse momentum dependent parton distribution functions (TMDs), parton-to-hadron fragmentation functions, and multi-parton correlation functions, were discussed extensively at the Duke workshop. In this paper, we summarize… ▽ More We present a summary of a recent workshop held at Duke University on Partonic Transverse Momentum in Hadrons: Quark Spin-Orbit Correlations and Quark-Gluon Interactions. The transverse momentum dependent parton distribution functions (TMDs), parton-to-hadron fragmentation functions, and multi-parton correlation functions, were discussed extensively at the Duke workshop. In this paper, we summarize first the theoretical issues concerning the study of partonic structure of hadrons at a future electron-ion collider (EIC) with emphasis on the TMDs. We then present simulation results on experimental studies of TMDs through measurements of single spin asymmetries (SSA) from semi-inclusive deep-inelastic scattering (SIDIS) processes with an EIC, and discuss the requirement of the detector for SIDIS measurements. The dynamics of parton correlations in the nucleon is further explored via a study of SSA in D (`D) production at large transverse momenta with the aim of accessing the unexplored tri-gluon correlation functions. The workshop participants identified the SSA measurements in SIDIS as a golden program to study TMDs in both the sea and valence quark regions and to study the role of gluons, with the Sivers asymmetry measurements as examples. Such measurements will lead to major advancement in our understanding of TMDs in the valence quark region, and more importantly also allow for the investigation of TMDs in the sea quark region along with a study of their evolution. △ Less

Submitted 4 February, 2011; v1 submitted 21 January, 2011; originally announced January 2011.

Comments: 44 pages 23 figures, summary of Duke EIC workshop on TMDs accepted by EPJA

Journal ref: Eur.Phys.J.A47:35,2011

Realistic Transverse Images of the Proton Charge and Magnetic Densities

Authors: Siddharth Venkat, John Arrington, Gerald A. Miller, Xiaohui Zhan

Abstract: We develop a technique, denoted as the finite radius approximation (FRA), that uses a two-dimensional version of the Shannon-Nyquist sampling theorem to determine transverse densities and their uncertainties from experimental quantities. Uncertainties arising from experimental uncertainties on the form factors and lack of measured data at high $Q^2$ are treated. A key feature of the FRA is that a… ▽ More We develop a technique, denoted as the finite radius approximation (FRA), that uses a two-dimensional version of the Shannon-Nyquist sampling theorem to determine transverse densities and their uncertainties from experimental quantities. Uncertainties arising from experimental uncertainties on the form factors and lack of measured data at high $Q^2$ are treated. A key feature of the FRA is that a form factor measured at a given value of $Q^2$ is related to a definite region in coordinate space. An exact relation between the FRA and the use of a Bessel series is derived. The proton Dirac form factor is well enough known such that the transverse charge density is very accurately known except for transverse separations $b$ less than about 0.1 fm. The Pauli form factor is well known to $Q^2$ of about 10 GeV$^2$, and this allows a reasonable, but improvable, determination of the anomalous magnetic moment density. △ Less

Submitted 5 November, 2010; v1 submitted 18 October, 2010; originally announced October 2010.

Comments: 11 pages, 9 figures

Report number: NT@UW-10-15

Journal ref: Phys.Rev.C83:015203,2011

Polarization Observables in Deuteron Photodisintegration below 360 MeV

Authors: J. Glister, G. Ron, B. W. Lee, R. Gilman, A. J. Sarty, S. Strauch, D. W. Higinbotham, E. Piasetzky, K. Allada, W. Armstrong, J. Arrington, A. Beck, F. Benmokhtar, B. L. Berman, W. Boeglin, E. Brash, A. Camsonne, J. Calarco, J. P. Chen, Seonho Choi, E. Chudakov, L. Coman, B. Craver, F. Cusanno, J. Dumas , et al. (64 additional authors not shown)

Abstract: High precision measurements of induced and transferred recoil proton polarization in d(polarized gamma, polarized p})n have been performed for photon energies of 277--357 MeV and theta_cm = 20 degrees -- 120 degrees. The measurements were motivated by a longstanding discrepancy between meson-baryon model calculations and data at higher energies. At the low energies of this experiment, theory con… ▽ More High precision measurements of induced and transferred recoil proton polarization in d(polarized gamma, polarized p})n have been performed for photon energies of 277--357 MeV and theta_cm = 20 degrees -- 120 degrees. The measurements were motivated by a longstanding discrepancy between meson-baryon model calculations and data at higher energies. At the low energies of this experiment, theory continues to fail to reproduce the data, indicating that either something is missing in the calculations and/or there is a problem with the accuracy of the nucleon-nucleon potential being used. △ Less

Submitted 9 March, 2010; originally announced March 2010.

Comments: 5 pages, 2 figures

Report number: JLAB-PHY-10-1133

Journal ref: Phys. Lett. B 697 (2011) 194

Polarization Transfer in the 4He(e,e'p)3H Reaction at Q^2 = 0.8 and 1.3 (GeV/c)^2

Authors: M. Paolone, S. P. Malace, S. Strauch, I. Albayrak, J. Arrington, B. L. Berman, E. J. Brash, B. Briscoe, A. Camsonne, J. -P. Chen, M. E. Christy, E. Chudakov, E. Cisbani, B. Craver, F. Cusanno, R. Ent, F. Garibaldi, R. Gilman, O. Glamazdin, J. Glister, D. W. Higinbotham, C. E. Hyde-Wright, Y. Ilieva, C. W. de Jager, X. Jiang , et al. (33 additional authors not shown)

Abstract: Proton recoil polarization was measured in the quasielastic 4He(e,e'p)3H reaction at Q^2 = 0.8 (GeV/c)^2 and 1.3 (GeV/c)^2 with unprecedented precision. The polarization-transfer coefficients are found to differ from those of the 1H(e,e' p) reaction, contradicting a relativistic distorted-wave approximation, and favoring either the inclusion of medium-modified proton form factors predicted by the… ▽ More Proton recoil polarization was measured in the quasielastic 4He(e,e'p)3H reaction at Q^2 = 0.8 (GeV/c)^2 and 1.3 (GeV/c)^2 with unprecedented precision. The polarization-transfer coefficients are found to differ from those of the 1H(e,e' p) reaction, contradicting a relativistic distorted-wave approximation, and favoring either the inclusion of medium-modified proton form factors predicted by the quark-meson coupling model or a spin-dependent charge-exchange final-state interaction. For the first time, the polarization-transfer ratio is studied as a function of the virtuality of the proton. △ Less

Submitted 23 August, 2010; v1 submitted 10 February, 2010; originally announced February 2010.

Journal ref: Phys.Rev.Lett.105:072001,2010

Hard Photodisintegration of a Proton Pair

Authors: I. Pomerantz, N. Bubis, K. Allada, A. Beck, S. Beck, B. L. Berman, W. Boeglin, A. Camsonne, M. Canan, K. Chirapatpimol, E. Cisbani, F. Cusanno, C. W. de Jager, C. Dutta, F. Garibaldi, O. Geagla, R. Gilman, J. Glister, D. W. Higinbotham, X. Jiang, A. T. Katramatou, E. Khrosinkova, B. Lee, J. J. LeRose, R. Lindgren , et al. (25 additional authors not shown)

Abstract: We present a study of high energy photodisintegration of proton-pairs through the gamma + 3He -> p+p+n channel. Photon energies from 0.8 to 4.7 GeV were used in kinematics corresponding to a proton pair with high relative momentum and a neutron nearly at rest. The s-11 scaling of the cross section, as predicted by the constituent counting rule for two nucleon photodisintegration, was observed fo… ▽ More We present a study of high energy photodisintegration of proton-pairs through the gamma + 3He -> p+p+n channel. Photon energies from 0.8 to 4.7 GeV were used in kinematics corresponding to a proton pair with high relative momentum and a neutron nearly at rest. The s-11 scaling of the cross section, as predicted by the constituent counting rule for two nucleon photodisintegration, was observed for the first time. The onset of the scaling is at a higher energy and the cross section is significantly lower than for deuteron (pn pair) photodisintegration. For photon energies below the scaling region, the scaled cross section was found to present a strong energy-dependent structure not observed in deuteron photodisintegration. △ Less

Submitted 26 November, 2009; v1 submitted 20 August, 2009; originally announced August 2009.

Comments: 7 pages, 3 figures, for submission to Phys. Lett. B

Report number: JLAB-PHY-09-1050

Journal ref: Phys.Lett.B684:106-109,2010