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Near-Threshold J/$ψ\to μ^+μ^-$ Photoproduction and the Gluonic Gravitational Form Factors of the Proton
Authors:
The J/ψ-007 Collaboration,
:,
S. Joosten,
Z. -E. Meziani,
S. Prasad,
J. Swartz,
B. Duran,
M. K. Jones,
H. Klest,
M. Paolone,
C. Peng,
W. Armstrong,
H. Atac,
E. Chudakov,
H. Bhatt,
D. Bhetuwal,
M. Boer,
A. Camsonne,
J. -P. Chen,
M. Dalton,
N. Deokar,
M. Diefenthaler,
J. Dunne,
L. El Fassi,
F. Flor
, et al. (35 additional authors not shown)
Abstract:
We report on the measurement of the two-dimensional differential cross section for near-threshold J/$ψ\to μ^+μ^-$ photoproduction from the J/$ψ$-007 experiment in Hall C at Jefferson Lab. Our results agree with the previously published J/$ψ\to e^+e^-$ results. We extract the integrated photoproduction cross section and find no evidence for open-charm contributions. A combined analysis of both deca…
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We report on the measurement of the two-dimensional differential cross section for near-threshold J/$ψ\to μ^+μ^-$ photoproduction from the J/$ψ$-007 experiment in Hall C at Jefferson Lab. Our results agree with the previously published J/$ψ\to e^+e^-$ results. We extract the integrated photoproduction cross section and find no evidence for open-charm contributions. A combined analysis of both decay channels following a Holographic QCD approach yields improved experimental constraints on the gluonic gravitational form factor $\mathcal{C}_g(t)$. Our results agree with recent lattice QCD calculations and we obtain $\mathcal{C}_g(t)$ with a comparable statistical precision to lattice QCD. Our results support a spatial picture where gluons dominate at larger radii with a confining inward pressure. This work provides new input for exploring the mechanical properties of gluons inside the proton.
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Submitted 24 February, 2026; v1 submitted 15 February, 2026;
originally announced February 2026.
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Long Range Outlook for Short-Range Correlations
Authors:
Nadia Fomin,
Or Hen,
Julian Kahlbow,
Dien Nguyen,
Jackson Pybus,
Noemi Rocco,
Misak Sargsian,
Sandra Nathaly Santiesteban,
Ronen Weiss,
Douglas W. Higinbotham,
Lawrence Weinstein,
Devi Adhikari,
Hisham Albataineh,
Massimiliano Alvioli,
Lorenzo Andreoli,
John Arrington,
Carlos Ayerbe Gayoso,
A. B. Balantekin,
Carlos Bertulani,
Hem Bhatt,
Sudip Bhattarai,
William J. Briscoe,
Sayak Chatterjee,
Hector Chinchay,
E. O. Cohn
, et al. (77 additional authors not shown)
Abstract:
Short range correlated (SRC) N N pairs are pairs of nucleons with high relative momentum (prel > kF where kF ~ 250 MeV/c is the Fermi momentum in medium to heavy nuclei) and lower center of mass momentum. The motivation for studying SRC pairs ranges from a desire to achieve a more comprehensive understanding of the many-body nuclear wave-function at high-resolution to searching for explicit QCD-dy…
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Short range correlated (SRC) N N pairs are pairs of nucleons with high relative momentum (prel > kF where kF ~ 250 MeV/c is the Fermi momentum in medium to heavy nuclei) and lower center of mass momentum. The motivation for studying SRC pairs ranges from a desire to achieve a more comprehensive understanding of the many-body nuclear wave-function at high-resolution to searching for explicit QCD-dynamics effects within the nuclear medium, not to mention connections to many other open problems in nuclear physics.
Exploring short-range correlations was one of the physics motivations for building CEBAF (now Jefferson Lab). Scientists used the high luminosity and high energy of this cutting-edge machine to find kinematics that cleanly showed the signals of short-range correlations. This paved the way in the last two decades for tremendous progress understanding these correlations. This paper reviews recent progress and highlights outstanding questions and areas that need further study.
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Submitted 14 January, 2026;
originally announced January 2026.
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Probing hard/soft factorization via beam-spin asymmetry in exclusive pion electroproduction from the proton
Authors:
Alicia C. Postuma,
Garth M. Huber,
D. J. Gaskell,
N. Heinrich,
T. Horn,
M. Junaid,
S. J. D. Kay,
V. Kumar,
P. Markowitz,
J. Roche,
R. Trotta,
A. Usman,
B. -G. Yu,
T. K. Choi,
K. -J. Kong,
S. Ali,
R. Ambrose,
D. Androic,
W. Armstrong,
A. Bandari,
V. Berdnikov,
H. Bhatt,
D. Bhetuwal,
D. Biswas,
M. Boer
, et al. (54 additional authors not shown)
Abstract:
Deep exclusive meson production (DEMP) reactions, such as $p(\vec{e},e'π^+)n$, provide opportunities to study the three-dimensional structure of the nucleon through differential cross section and beam- and target-spin asymmetry measurements. This work aims to probe the onset of the hard/soft factorization regime through the exclusive $p(\vec{e},e'π^+)n$ reaction, as measured in the KaonLT experime…
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Deep exclusive meson production (DEMP) reactions, such as $p(\vec{e},e'π^+)n$, provide opportunities to study the three-dimensional structure of the nucleon through differential cross section and beam- and target-spin asymmetry measurements. This work aims to probe the onset of the hard/soft factorization regime through the exclusive $p(\vec{e},e'π^+)n$ reaction, as measured in the KaonLT experiment at Jefferson Lab Hall C. A 10.6 GeV longitudinally polarized electron beam was incident on an unpolarized liquid hydrogen target, and the scattered electron and produced meson were detected in two magnetic focusing spectrometers, enabling precision cross section measurements. The cross section ratio $σ_{LT'}/σ_0$ was extracted from the beam-spin asymmetry $A_{LU}$. The $t$-dependence of $σ_{LT'}/σ_0$ was determined at fixed $Q^2$ and $x_B$ over a range of kinematics from $2<Q^2<6$ GeV$^2$ above the resonance region ($W>2$ GeV). Furthermore, these data are combined with recent results from CLAS/CLAS12 to determine the $Q^2$-dependence of $σ_{LT'}/σ_0$ at two ($x_B$, $t$) settings. This was fairly flat, with $Q^2$ not having a measurable effect on the value of $σ_{LT'}/σ_0$ in the range explored. Results are compared to predictions from the generalized parton distribution (GPD) formalism, which relies explicitly on hard/soft factorization, and Regge formalism. The Regge models better predict $σ_{LT'}/σ_0$, which suggests that the factorization regime is not yet reached.
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Submitted 1 December, 2025;
originally announced December 2025.
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Flavor, transverse momentum, and azimuthal dependence of charged pion multiplicities in SIDIS with 10.6 GeV electrons
Authors:
Hall C SIDIS Collaboration,
P. Bosted,
H. Bhatt,
S. Jia,
W. Armstrong,
D. Dutta,
R. Ent,
D. Gaskell,
E. Kinney,
H. Mkrtchyan,
S. Ali,
R. Ambrose,
D. Androic,
C. Ayerbe Gayoso,
A. Bandari,
V. Berdnikov,
D. Bhetuwal,
D. Biswas,
M. Boer,
E. Brash,
A. Camsonne,
M. Cardona,
J. P. Chen,
J. Chen,
M. Chen
, et al. (46 additional authors not shown)
Abstract:
Measurements of SIDIS multiplicities for $π^+$ and $π^-$ from proton and deuteron targets are reported on a grid of hadron kinematic variables $z$, $P_{T}$, and $φ^{*}$ for leptonic kinematic variables in the range $0.3<x<0.6$ and $3<Q^2<5$ GeV$^2$. Data were acquired in 2018-2019 at Jefferson Lab Hall C with a 10.6~GeV electron beam impinging on 10-cm-long liquid hydrogen and deuterium targets. S…
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Measurements of SIDIS multiplicities for $π^+$ and $π^-$ from proton and deuteron targets are reported on a grid of hadron kinematic variables $z$, $P_{T}$, and $φ^{*}$ for leptonic kinematic variables in the range $0.3<x<0.6$ and $3<Q^2<5$ GeV$^2$. Data were acquired in 2018-2019 at Jefferson Lab Hall C with a 10.6~GeV electron beam impinging on 10-cm-long liquid hydrogen and deuterium targets. Scattered electrons and charged pions were detected in the HMS and SHMS spectrometers, respectively. The multiplicities were fitted for each bin in $(x,~Q^2,~z,~P_{t})$ to extract the $φ^{*}$ independent $M_0$ and the azimuthal modulations $\langle \cos(φ^{*}) \rangle$ and $\langle \cos(2φ^{*}) \rangle$. The $P_t$-dependence of the $M_0$ results was found to be remarkably consistent for the four cases studied: $ep\rightarrow e π^+ X$, $ep\rightarrow e π^- X$, $ed\rightarrow e π^+ X$, $ed\rightarrow e π^- X$ over the range $0<P_t<0.4$ GeV, as were the multiplicities evaluated near $φ^* = 180^\circ$ over the extended range $0<P_t<0.7$ GeV. The Gaussian widths of the $P_t$-dependence exhibit a quadratic increase with $z$. The $\cos(φ^{*})$ modulations were found to be consistent with zero for $π^+$, in agreement with previous world data, while the $π^-$ moments were, in many cases, significantly greater than zero. The $\cos(2φ^{*})$ modulations were found to be consistent with zero. The higher statistical precision of this dataset compared to previously published data should allow improved determinations of quark transverse momentum distributions and higher twist contributions.
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Submitted 22 June, 2026; v1 submitted 3 October, 2025;
originally announced October 2025.
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The SHMS 11 GeV/c Spectrometer in Hall C at Jefferson Lab
Authors:
S. Ali,
A. Ahmidouch,
G. R. Ambrose,
A. Asaturyan,
C. Ayerbe Gayoso,
J. Benesch,
V. Berdnikov,
H. Bhatt,
D. Bhetuwal,
D. Biswas,
P. Brindza,
M. Bukhari,
M. Burton,
R. Carlini,
M. Carmignotto,
M. E. Christy,
C. Cotton,
J. Crafts,
D. Day,
S. Danagoulian,
A. Dittmann,
D. H. Dongwi,
B. Duran,
D. Dutta,
R. Ent
, et al. (50 additional authors not shown)
Abstract:
The Super High Momentum Spectrometer (SHMS) has been built for Hall C at the Thomas Jefferson National Accelerator Facility (Jefferson Lab). With a momentum capability reaching 11 GeV/c, the SHMS provides measurements of charged particles produced in electron-scattering experiments using the maximum available beam energy from the upgraded Jefferson Lab accelerator. The SHMS is an ion-optics magnet…
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The Super High Momentum Spectrometer (SHMS) has been built for Hall C at the Thomas Jefferson National Accelerator Facility (Jefferson Lab). With a momentum capability reaching 11 GeV/c, the SHMS provides measurements of charged particles produced in electron-scattering experiments using the maximum available beam energy from the upgraded Jefferson Lab accelerator. The SHMS is an ion-optics magnetic spectrometer comprised of a series of new superconducting magnets which transport charged particles through an array of triggering, tracking, and particle-identification detectors that measure momentum, energy, angle and position in order to allow kinematic reconstruction of the events back to their origin at the scattering target. The detector system is protected from background radiation by a sophisticated shielding enclosure. The entire spectrometer is mounted on a rotating support structure which permits measurements to be taken with a large acceptance over laboratory scattering angles from 5.5 to 40 degrees, thus allowing a wide range of low cross-section experiments to be conducted. These experiments complement and extend the previous Hall C research program to higher energies.
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Submitted 28 November, 2025; v1 submitted 9 March, 2025;
originally announced March 2025.
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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…
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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.
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Submitted 15 October, 2024;
originally announced October 2024.
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Quasielastic $\overrightarrow{^{3}\mathrm{He}}(\overrightarrow{e},{e'})$ Asymmetry in the Threshold Region
Authors:
M. Nycz,
W. Armstrong,
T. Averett,
C. Ayerbe Gayoso,
X. Bai,
J. Bane,
S. Barcus,
J. Benesch,
H. Bhatt,
D. Bhetuwal,
D. Biswas,
A. Camsonne,
G. Cates,
J-P. Chen,
J. Chen,
M. Chen,
C. Cotton,
M-M. Dalton,
A. Deltuva,
A. Deur,
B. Dhital,
B. Duran,
S. C. Dusa,
I. Fernando,
E. Fuchey
, et al. (75 additional authors not shown)
Abstract:
A measurement of the double-spin asymmetry from electron-$^{3}$He scattering in the threshold region of two- and three-body breakup of $^{3}$He was performed at Jefferson Lab, for Q$^{2}$ values of 0.1 and 0.2 (GeV/$c$)$^{2}$. The results of this measurement serve as a stringent test of our understanding of few-body systems. When compared with calculations from plane wave impulse approximation and…
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A measurement of the double-spin asymmetry from electron-$^{3}$He scattering in the threshold region of two- and three-body breakup of $^{3}$He was performed at Jefferson Lab, for Q$^{2}$ values of 0.1 and 0.2 (GeV/$c$)$^{2}$. The results of this measurement serve as a stringent test of our understanding of few-body systems. When compared with calculations from plane wave impulse approximation and Faddeev theory, we found that the Faddeev calculations, which use modern nuclear potentials and prescriptions for meson-exchange currents, demonstrate an overall good agreement with data.
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Submitted 24 September, 2024;
originally announced September 2024.
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Pion electroproduction measurements in the nucleon resonance region
Authors:
R. Li,
N. Sparveris,
H. Atac,
M. K. Jones,
M. Paolone,
Z. Akbar,
M. Ali,
C. Ayerbe Gayoso,
V. Berdnikov,
D. Biswas,
M. Boer,
A. Camsonne,
J. -P. Chen,
M. Diefenthaler,
B. Duran,
D. Dutta,
D. Gaskell,
O. Hansen,
F. Hauenstein,
N. Heinrich,
W. Henry,
T. Horn,
G. M. Huber,
S. Jia,
S. Joosten
, et al. (24 additional authors not shown)
Abstract:
We report new pion electroproduction measurements in the $Δ(1232)$ resonance, utilizing the SHMS - HMS magnetic spectrometers of Hall C at Jefferson Lab. The data focus on a region that exhibits a strong and rapidly changing interplay of the mesonic cloud and quark-gluon dynamics in the nucleon. The results are in reasonable agreement with models that employ pion cloud effects and chiral effective…
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We report new pion electroproduction measurements in the $Δ(1232)$ resonance, utilizing the SHMS - HMS magnetic spectrometers of Hall C at Jefferson Lab. The data focus on a region that exhibits a strong and rapidly changing interplay of the mesonic cloud and quark-gluon dynamics in the nucleon. The results are in reasonable agreement with models that employ pion cloud effects and chiral effective field theory calculations, but at the same time they suggest that an improvement is required to the theoretical calculations and provide valuable input that will allow their refinements. The data illustrate the potential of the magnetic spectrometers setup in Hall C towards the study the $Δ(1232)$ resonance. These first reported results will be followed by a series of measurements in Hall C, that will expand the studies of the $Δ(1232)$ resonance offering a high precision insight within a wide kinematic range from low to high momentum transfers.
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Submitted 5 September, 2024;
originally announced September 2024.
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Flavor Dependence of Charged Pion Fragmentation Functions
Authors:
H. Bhatt,
P. Bosted,
S. Jia,
W. Armstrong,
D. Dutta,
R. Ent,
D. Gaskell,
E. Kinney,
H. Mkrtchyan,
S. Ali,
R. Ambrose,
D. Androic,
C. Ayerbe Gayoso,
A. Bandari,
V. Berdnikov,
D. Bhetuwal,
D. Biswas,
M. Boer,
E. Brash,
A. Camsonne,
J. P. Chen,
J. Chen,
M. Chen,
E. M. Christy,
S. Covrig
, et al. (45 additional authors not shown)
Abstract:
We have measured the flavor dependence of multiplicities for pi^+ and pi^- production in semi-inclusive deep-inelastic scattering (SIDIS) on proton and deuteron targets to explore a possible charge symmetry violation in fragmentation functions. The experiment used an electron beam with energies of 10.2 and 10.6 GeV at Jefferson Lab and the Hall-C spectrometers. The electron kinematics spanned the…
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We have measured the flavor dependence of multiplicities for pi^+ and pi^- production in semi-inclusive deep-inelastic scattering (SIDIS) on proton and deuteron targets to explore a possible charge symmetry violation in fragmentation functions. The experiment used an electron beam with energies of 10.2 and 10.6 GeV at Jefferson Lab and the Hall-C spectrometers. The electron kinematics spanned the range 0.3<x<0.6, 2<Q^2<5.5 GeV^2, and 4<W^2<11 GeV^2. The pion fractional momentum range was 0.3< z <0.7, and the transverse momentum range was 0<p_T<0.25 GeV/c. Assuming factorization at low p_T and allowing for isospin breaking, we find that the results can be described by two "favored" and two "un-favored" effective low $p_T$ fragmentation functions that are flavor-dependent. However, they converge to a common flavor-independent value at the lowest x or highest W of this experiment.
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Submitted 5 September, 2024; v1 submitted 29 August, 2024;
originally announced August 2024.
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Measured proton electromagnetic structure deviates from theoretical predictions
Authors:
R. Li,
N. Sparveris,
H. Atac,
M. K. Jones,
M. Paolone,
Z. Akbar,
C. Ayerbe Gayoso,
V. Berdnikov,
D. Biswas,
M. Boer,
A. Camsonne,
J. -P. Chen,
M. Diefenthaler,
B. Duran,
D. Dutta,
D. Gaskell,
O. Hansen,
F. Hauenstein,
N. Heinrich,
W. Henry,
T. Horn,
G. M. Huber,
S. Jia,
S. Joosten,
A. Karki
, et al. (22 additional authors not shown)
Abstract:
The visible world is founded on the proton, the only composite building block of matter that is stable in nature. Consequently, understanding the formation of matter relies on explaining the dynamics and the properties of the proton's bound state.A fundamental property of the proton involves the response of the system to an external electromagnetic field. It is characterized by the electromagnetic…
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The visible world is founded on the proton, the only composite building block of matter that is stable in nature. Consequently, understanding the formation of matter relies on explaining the dynamics and the properties of the proton's bound state.A fundamental property of the proton involves the response of the system to an external electromagnetic field. It is characterized by the electromagnetic polarizabilities that describe how easily the charge and magnetization distributions inside the system are distorted by the electromagnetic field. Moreover, the generalized polarizabilities map out the resulting deformation of the densities in a proton subject to an electromagnetic field. They disclose essential information about the underlying system dynamics and provide a key for decoding the proton structure in terms of the theory of the strong interaction that binds its elementary quark and gluon constituents. Of particular interest is a puzzle in the electric generalized polarizability of the proton that remains unresolved for two decades. Here we report measurements of the proton's electromagnetic generalized polarizabilities at low four-momentum transfer squared. We show evidence of an anomaly to the behaviour of the proton's electric generalized polarizability that contradicts the predictions of nuclear theory and derive its signature in the spatial distribution of the induced polarization in the proton. The reported measurements suggest the presence of a new, not-yet-understood dynamical mechanism in the proton and present notable challenges to the nuclear theory.
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Submitted 20 October, 2022;
originally announced October 2022.
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Determining the Proton's Gluonic Gravitational Form Factors
Authors:
B. Duran,
Z. -E. Meziani,
S. Joosten,
M. K. Jones,
S. Prasad,
C. Peng,
W. Armstrong,
H. Atac,
E. Chudakov,
H. Bhatt,
D. Bhetuwal,
M. Boer,
A. Camsonne,
J. -P. Chen,
M. M. Dalton,
N. Deokar,
M. Diefenthaler,
J. Dunne,
L. El Fassi,
E. Fuchey,
H. Gao,
D. Gaskell,
O. Hansen,
F. Hauenstein,
D. Higinbotham
, et al. (30 additional authors not shown)
Abstract:
The proton is one of the main building blocks of all visible matter in the universe. Among its intrinsic properties are its electric charge, mass, and spin. These emerge from the complex dynamics of its fundamental constituents, quarks and gluons, described by the theory of quantum chromodynamics (QCD). Using electron scattering, its electric charge and spin, shared among the quark constituents, h…
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The proton is one of the main building blocks of all visible matter in the universe. Among its intrinsic properties are its electric charge, mass, and spin. These emerge from the complex dynamics of its fundamental constituents, quarks and gluons, described by the theory of quantum chromodynamics (QCD). Using electron scattering, its electric charge and spin, shared among the quark constituents, have been the topic of active investigation. An example is the novel precision measurement of the proton's electric charge radius. In contrast, little is known about the proton's inner mass density, dominated by the energy carried by the gluons, which are hard to access through electron scattering since gluons carry no electromagnetic charge. Here, we chose to probe this gluonic gravitational density using a small color dipole, the $J/ψ$ particle, through its threshold photoproduction. From our data, we determined, for the first time, the proton's gluonic gravitational form factors. We used a variety of models and determined, in all cases, a mass radius that is notably smaller than the electric charge radius. In some cases, the determined radius, although model dependent, is in excellent agreement with first-principle predictions from lattice QCD. This work paves the way for a deeper understanding of the salient role of gluons in providing gravitational mass to visible matter.
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Submitted 7 February, 2023; v1 submitted 11 July, 2022;
originally announced July 2022.
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First Measurement of the EMC Effect in $^{10}$B and $^{11}$B
Authors:
A. Karki,
D. Biswas,
F. A. Gonzalez,
W. Henry,
C. Morean,
A. Nadeeshani,
A. Sun,
D. Abrams,
Z. Ahmed,
B. Aljawrneh,
S. Alsalmi,
R. Ambrose,
D. Androic,
W. Armstrong,
J. Arrington,
A. Asaturyan,
K. Assumin-Gyimah,
C. Ayerbe Gayoso,
A. Bandari,
J. Bane,
J. Barrow,
S. Basnet,
V. Berdnikov,
H. Bhatt,
D. Bhetuwal
, et al. (72 additional authors not shown)
Abstract:
The nuclear dependence of the inclusive inelastic electron scattering cross section (the EMC effect) has been measured for the first time in $^{10}$B and $^{11}$B. Previous measurements of the EMC effect in $A \leq 12$ nuclei showed an unexpected nuclear dependence; $^{10}$B and $^{11}$B were measured to explore the EMC effect in this region in more detail. Results are presented for $^9$Be,…
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The nuclear dependence of the inclusive inelastic electron scattering cross section (the EMC effect) has been measured for the first time in $^{10}$B and $^{11}$B. Previous measurements of the EMC effect in $A \leq 12$ nuclei showed an unexpected nuclear dependence; $^{10}$B and $^{11}$B were measured to explore the EMC effect in this region in more detail. Results are presented for $^9$Be, $^{10}$B, $^{11}$B, and $^{12}$C at an incident beam energy of 10.6~GeV. The EMC effect in the boron isotopes was found to be similar to that for $^9$Be and $^{12}$C, yielding almost no nuclear dependence in the EMC effect in the range $A=4-12$. This represents important, new data supporting the hypothesis that the EMC effect depends primarily on the local nuclear environment due to the cluster structure of these nuclei.
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Submitted 31 July, 2023; v1 submitted 8 July, 2022;
originally announced July 2022.
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Constraints on the onset of color transparency from quasi-elastic $^{12}$C$(e,e'p)$ up to $Q^2=\,14.2\,$(GeV$/c)^2$
Authors:
D. Bhetuwal,
J. Matter,
H. Szumila-Vance,
C. Ayerbe Gayoso,
M. L. Kabir,
D. Dutta,
R. Ent,
D. Abrams,
Z. Ahmed,
B. Aljawrneh,
S. Alsalmi,
R. Ambrose,
D. Androic,
W. Armstrong,
A. Asaturyan,
K. Assumin-Gyimah,
A. Bandari,
S. Basnet,
V. Berdnikov,
H. Bhatt,
D. Biswas,
W. U. Boeglin,
P. Bosted,
E. Brash,
M. H. S. Bukhari
, et al. (65 additional authors not shown)
Abstract:
Quasi-elastic scattering on $^{12}$C$(e,e'p)$ was measured in Hall C at Jefferson Lab for space-like 4-momentum transfer squared $Q^2$ in the range of 8--14.2\,(GeV/$c$)$^2$ with proton momenta up to 8.3\,GeV/$c$. The experiment was carried out in the upgraded Hall C at Jefferson Lab. It used the existing high momentum spectrometer and the new super high momentum spectrometer to detect the scatter…
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Quasi-elastic scattering on $^{12}$C$(e,e'p)$ was measured in Hall C at Jefferson Lab for space-like 4-momentum transfer squared $Q^2$ in the range of 8--14.2\,(GeV/$c$)$^2$ with proton momenta up to 8.3\,GeV/$c$. The experiment was carried out in the upgraded Hall C at Jefferson Lab. It used the existing high momentum spectrometer and the new super high momentum spectrometer to detect the scattered electrons and protons in coincidence. The nuclear transparency was extracted as the ratio of the measured yield to the yield calculated in the plane wave impulse approximation. Additionally, the transparency of the $1s_{1/2}$ and $1p_{3/2}$ shell protons in $^{12}$C was extracted, and the asymmetry of the missing momentum distribution was examined for hints of the quantum chromodynamics prediction of Color Transparency. All of these results were found to be consistent with traditional nuclear physics and inconsistent with the onset of Color Transparency.
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Submitted 14 August, 2023; v1 submitted 26 May, 2022;
originally announced May 2022.
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Deeply virtual Compton scattering cross section at high Bjorken $x_B$
Authors:
F. Georges,
M. N. H. Rashad,
A. Stefanko,
M. Dlamini,
B. Karki,
S. F. Ali,
P-J. Lin,
H-S Ko,
N. Israel,
D. Adikaram,
Z. Ahmed,
H. Albataineh,
B. Aljawrneh,
K. Allada,
S. Allison,
S. Alsalmi,
D. Androic,
K. Aniol,
J. Annand,
H. Atac,
T. Averett,
C. Ayerbe Gayoso,
X. Bai,
J. Bane,
S. Barcus
, et al. (137 additional authors not shown)
Abstract:
We report high-precision measurements of the Deeply Virtual Compton Scattering (DVCS) cross section at high values of the Bjorken variable $x_B$. DVCS is sensitive to the Generalized Parton Distributions of the nucleon, which provide a three-dimensional description of its internal constituents. Using the exact analytic expression of the DVCS cross section for all possible polarization states of th…
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We report high-precision measurements of the Deeply Virtual Compton Scattering (DVCS) cross section at high values of the Bjorken variable $x_B$. DVCS is sensitive to the Generalized Parton Distributions of the nucleon, which provide a three-dimensional description of its internal constituents. Using the exact analytic expression of the DVCS cross section for all possible polarization states of the initial and final electron and nucleon, and final state photon, we present the first experimental extraction of all four helicity-conserving Compton Form Factors (CFFs) of the nucleon as a function of $x_B$, while systematically including helicity flip amplitudes. In particular, the high accuracy of the present data demonstrates sensitivity to some very poorly known CFFs.
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Submitted 10 January, 2022;
originally announced January 2022.
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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…
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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$.
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Submitted 21 March, 2022; v1 submitted 2 March, 2021;
originally announced March 2021.
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Deep exclusive electroproduction of $π^0$ at high $Q^2$ in the quark valence regime
Authors:
The Jefferson Lab Hall A Collaboration,
M. Dlamini,
B. Karki,
S. F. Ali,
P-J. Lin,
F. Georges,
H-S Ko,
N. Israel,
M. N. H. Rashad,
A. Stefanko,
D. Adikaram,
Z. Ahmed,
H. Albataineh,
B. Aljawrneh,
K. Allada,
S. Allison,
S. Alsalmi,
D. Androic,
K. Aniol,
J. Annand,
H. Atac,
T. Averett,
C. Ayerbe Gayoso,
X. Bai,
J. Bane
, et al. (137 additional authors not shown)
Abstract:
We report measurements of the exclusive neutral pion electroproduction cross section off protons at large values of $x_B$ (0.36, 0.48 and 0.60) and $Q^2$ (3.1 to 8.4 GeV$^2$) obtained from Jefferson Lab Hall A experiment E12-06-014. The corresponding structure functions $dσ_L/dt+εdσ_T/dt$, $dσ_{TT}/dt$, $dσ_{LT}/dt$ and $dσ_{LT'}/dt$ are extracted as a function of the proton momentum transfer…
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We report measurements of the exclusive neutral pion electroproduction cross section off protons at large values of $x_B$ (0.36, 0.48 and 0.60) and $Q^2$ (3.1 to 8.4 GeV$^2$) obtained from Jefferson Lab Hall A experiment E12-06-014. The corresponding structure functions $dσ_L/dt+εdσ_T/dt$, $dσ_{TT}/dt$, $dσ_{LT}/dt$ and $dσ_{LT'}/dt$ are extracted as a function of the proton momentum transfer $t-t_{min}$. The results suggest the amplitude for transversely polarized virtual photons continues to dominate the cross-section throughout this kinematic range. The data are well described by calculations based on transversity Generalized Parton Distributions coupled to a helicity flip Distribution Amplitude of the pion, thus providing a unique way to probe the structure of the nucleon.
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Submitted 25 October, 2021; v1 submitted 22 November, 2020;
originally announced November 2020.
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Ruling out color transparency in quasi-elastic $^{12}$C(e,e'p) up to $Q^2$ of 14.2 (GeV/c)$^2$
Authors:
D. Bhetuwal,
J. Matter,
H. Szumila-Vance,
M. L. Kabir,
D. Dutta,
R. Ent,
D. Abrams,
Z. Ahmed,
B. Aljawrneh,
S. Alsalmi,
R. Ambrose,
D. Androic,
W. Armstrong,
A. Asaturyan,
K. Assumin-Gyimah,
C. Ayerbe Gayoso,
A. Bandari,
S. Basnet,
V. Berdnikov,
H. Bhatt,
D. Biswas,
W. U. Boeglin,
P. Bosted,
E. Brash,
M. H. S. Bukhari
, et al. (65 additional authors not shown)
Abstract:
Quasielastic $^{12}$C$(e,e'p)$ scattering was measured at space-like 4-momentum transfer squared $Q^2$~=~8, 9.4, 11.4, and 14.2 (GeV/c)$^2$, the highest ever achieved to date. Nuclear transparency for this reaction was extracted by comparing the measured yield to that expected from a plane-wave impulse approximation calculation without any final state interactions. The measured transparency was co…
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Quasielastic $^{12}$C$(e,e'p)$ scattering was measured at space-like 4-momentum transfer squared $Q^2$~=~8, 9.4, 11.4, and 14.2 (GeV/c)$^2$, the highest ever achieved to date. Nuclear transparency for this reaction was extracted by comparing the measured yield to that expected from a plane-wave impulse approximation calculation without any final state interactions. The measured transparency was consistent with no $Q^2$ dependence, up to proton momenta of 8.5~GeV/c, ruling out the quantum chromodynamics effect of color transparency at the measured $Q^2$ scales in exclusive $(e,e'p)$ reactions. These results impose strict constraints on models of color transparency for protons.
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Submitted 1 March, 2021; v1 submitted 1 November, 2020;
originally announced November 2020.
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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…
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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.
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Submitted 17 June, 2020; v1 submitted 20 January, 2020;
originally announced January 2020.
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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…
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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.
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Submitted 24 September, 2019; v1 submitted 17 February, 2019;
originally announced February 2019.
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First Measurements of the Double-Polarization Observables $F$, $P$, and $H$ in $ω$ Photoproduction off Transversely Polarized Protons in the $N^\ast$ Resonance Region
Authors:
P. Roy,
S. Park,
V. Crede,
A. V. Anisovich,
E. Klempt,
V. A. Nikonov,
A. V. Sarantsev,
N. C. Wei,
F. Huang,
K. Nakayama,
K. P. Adhikari,
S. Adhikari,
G. Angelini,
H. Avakian,
L. Barion,
M. Battaglieri,
I. Bedlinskiy,
A. S. Biselli,
S. Boiarinov,
W. J. Briscoe,
J. Brock,
W. K. Brooks,
V. D. Burkert,
F. Cao,
C. Carlin
, et al. (123 additional authors not shown)
Abstract:
First measurements of double-polarization observables in $ω$ photoproduction off the proton are presented using transverse target polarization and data from the CEBAF Large Acceptance Spectrometer (CLAS) FROST experiment at Jefferson Lab. The beam-target asymmetry $F$ has been measured using circularly polarized, tagged photons in the energy range 1200 - 2700 MeV, and the beam-target asymmetries…
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First measurements of double-polarization observables in $ω$ photoproduction off the proton are presented using transverse target polarization and data from the CEBAF Large Acceptance Spectrometer (CLAS) FROST experiment at Jefferson Lab. The beam-target asymmetry $F$ has been measured using circularly polarized, tagged photons in the energy range 1200 - 2700 MeV, and the beam-target asymmetries $H$ and $P$ have been measured using linearly polarized tagged photons in the energy range 1200 - 2000 MeV. These measurements significantly increase the database on polarization observables. The results are included in two partial-wave analyses and reveal significant contributions from several nucleon ($N^\ast$) resonances. In particular, contributions from new $N^\ast$ resonances listed in the Review of Particle Properties are observed, which aid in reaching the goal of mapping out the nucleon resonance spectrum.
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Submitted 1 May, 2019; v1 submitted 5 December, 2018;
originally announced December 2018.
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Tagged EMC Measurements on Light Nuclei
Authors:
Whitney Armstrong,
John Arrington,
Ian Cloet,
Kawtar Hafidi,
Mohammad Hattawy,
David Potteveld,
Paul Reimer,
Seamus Riordan,
Z. Yi,
Jacques Ball,
Maxime Defurne,
Michel Garcon,
Herve Moutarde,
Sebastien Procureur,
Franck Sabatie,
Wim Cosyn,
Malek Mazouz,
Alberto Accardi,
Julien Bettane,
Gabriel Charles,
Raphael Dupre,
Michel Guidal,
Dominique Marchand,
Carlos Munoz,
Silvia Niccolai
, et al. (28 additional authors not shown)
Abstract:
We propose to measure tagged deep inelastic scattering from light nuclei (deuterium and $^4$He) by detecting the low energy nuclear spectator recoil (p, $^3$H and $^3$He) in addition to the scattered electron. The proposed experiment will provide stringent tests leading to clear differentiation between the many models describing the EMC effect, by accessing the bound nucleon virtuality through its…
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We propose to measure tagged deep inelastic scattering from light nuclei (deuterium and $^4$He) by detecting the low energy nuclear spectator recoil (p, $^3$H and $^3$He) in addition to the scattered electron. The proposed experiment will provide stringent tests leading to clear differentiation between the many models describing the EMC effect, by accessing the bound nucleon virtuality through its initial momentum at the point of interaction. Indeed, conventional nuclear physics explanations of the EMC effect mainly based on Fermi motion and binding effects yield very different predictions than more exotic scenarios, where bound nucleons basically loose their identity when embedded in the nuclear medium. By distinguishing events where the interacting nucleon was slow, as described by a mean field scenario, or fast, very likely belonging to a correlated pair, will clearly indicate which phenomenon is relevant to explain the EMC effect. An important challenge for such measurements using nuclear spectators is the control of the theoretical framework and, in particular, final state interactions. This experiment will directly provide the necessary data needed to test our understanding of spectator tagging and final state interactions in $^2$H and $^4$He and their impact on the semi-inclusive measurements of the EMC effect described above.
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Submitted 2 August, 2017;
originally announced August 2017.
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Partonic Structure of Light Nuclei
Authors:
Whitney Armstrong,
John Arrington,
Ian Cloet,
Kawtar Hafidi,
Mohammad Hattawy,
David Potteveld,
Paul Reimer,
Seamus Riordan,
Z. Yi,
Jacques Ball,
Maxime Defurne,
Michel Garcon,
Herve Moutarde,
Sebastien Procureur,
Franck Sabatie,
Wim Cosyn,
Malek Mazouz,
Julien Bettane,
Gabriel Charles,
Raphael Dupre,
Michel Guidal,
Dominique Marchand,
Carlos Munoz,
Silvia Niccolai,
Eric Voutier
, et al. (23 additional authors not shown)
Abstract:
We propose to study the partonic structure of $^4$He by measuring the Beam Spin Asymmetry (BSA) in coherent Deeply Virtual Compton Scattering (DVCS) and the differential cross-section of the Deeply Virtual Meson Production (DVMP) of the $φ$. Despite its simple structure, a light nucleus such as $^4$He has a density and a binding energy comparable to that of heavier nuclei. Therefore, by studying…
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We propose to study the partonic structure of $^4$He by measuring the Beam Spin Asymmetry (BSA) in coherent Deeply Virtual Compton Scattering (DVCS) and the differential cross-section of the Deeply Virtual Meson Production (DVMP) of the $φ$. Despite its simple structure, a light nucleus such as $^4$He has a density and a binding energy comparable to that of heavier nuclei. Therefore, by studying $^4$He nucleus, one can learn typical features of the partonic structure of atomic nuclei.
The combination of CLAS12 and the ALERT detector provides a unique opportunity to study both the quark and gluon structure of a dense light nucleus. Coherent exclusive DVCS off $^4$He will probe the transverse spatial distribution of quarks in the nucleus as a function of the quarks' longitudinal momentum fraction, $x$. In parallel, the average spatial transverse gluon density of the $^4$He nucleus will be extracted within a GPD framework using the measured longitudinal cross-section for coherent $φ$ production in a similar range of $x$. Additionally, threshold effects of $φ$ production can be explored by exploiting the ALERT detector's large acceptance for low $|t|$ events.
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Submitted 5 August, 2017; v1 submitted 2 August, 2017;
originally announced August 2017.
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Spectator-Tagged Deeply Virtual Compton Scattering on Light Nuclei
Authors:
Whitney Armstrong,
John Arrington,
Ian Cloët,
Adam Freese,
Kawtar Hafidi,
Mohammad Hattawy,
Seamus Riordan,
Sereres Johnston,
David Potteveld,
Paul Reimer,
Zhihong Ye,
Jacques Ball,
Maxime Defurne,
Michel Garcon,
Herve Moutarde,
Sebastien Procureur,
Franck Sabatie,
Wim Cosyn,
Malek Mazouz,
Alberto Accardi,
Julien Bettane,
Gabriel Charles,
Raphael Dupre,
Michel Guidal,
Dominique Marchand
, et al. (31 additional authors not shown)
Abstract:
The three-dimensional picture of quarks and gluons in the proton is set to be revealed through Deeply virtual Compton scattering while a critically important puzzle in the one-dimensional picture remains, namely, the origins of the EMC effect. Incoherent nuclear DVCS, i.e. DVCS on a nucleon inside a nucleus, can reveal the 3D partonic structure of the bound nucleon and shed a new light on the EMC…
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The three-dimensional picture of quarks and gluons in the proton is set to be revealed through Deeply virtual Compton scattering while a critically important puzzle in the one-dimensional picture remains, namely, the origins of the EMC effect. Incoherent nuclear DVCS, i.e. DVCS on a nucleon inside a nucleus, can reveal the 3D partonic structure of the bound nucleon and shed a new light on the EMC effect. However, the Fermi motion of the struck nucleon, off-shell effects and final-state interactions (FSIs) complicate this parton level interpretation. We propose here a measurement of incoherent DVCS with a tagging of the recoiling spectator system (nucleus A-1) to systematically control nuclear effects. Through spectator-tagged DVCS, a fully detected final state presents a unique opportunity to systematically study these nuclear effects and cleanly observe possible modification of the nucleon's quark distributions.
We propose to measure the DVCS beam-spin asymmetries (BSAs) on $^4$He and deuterium targets. The reaction $^4$He$(e,e^{\prime}γ\,p\,^3$H$)$ with a fully detected final state has the rare ability to simultaneously quantify FSIs, measure initial nucleon momentum, and provide a sensitive probe to other nuclear effects at the parton level. The DVCS BSA on a (quasi-free) neutron will be measured by tagging a spectator proton with a deuteron target. Similarly, a bound neutron measurement detects a spectator $^3$He off a $^4$He target. These two observables will allow for a self-contained measurement of the neutron off-forward EMC Effect.
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Submitted 2 August, 2017;
originally announced August 2017.
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A Search for the LHCb Charmed 'Pentaquark' using Photo-Production of $J/ψ$ at Threshold in Hall C at Jefferson Lab
Authors:
Z. -E. Meziani,
S. Joosten,
M. Paolone,
E. Chudakov,
M. Jones,
K. Adhikari,
K. Aniol,
W. Armstrong,
J. Arrington,
A. Asaturyan,
H. Atac,
S. Bae,
H. Bhatt,
D. Bhetuwal,
J. -P. Chen,
X. Chen,
H. Choi,
S. Choi,
M. Diefenthaler,
J. Dunne,
R. Dupré,
B. Duran,
D. Dutta,
L. El-Fassi,
Q. Fu
, et al. (34 additional authors not shown)
Abstract:
We propose to measure the photo-production cross section of $J/ψ$ near threshold, in search of the recently observed LHCb hidden-charm resonances $P_c$(4380) and $P_c$(4450) consistent with 'pentaquarks'. The observation of these resonances in photo-production will provide strong evidence of the true resonance nature of the LHCb states, distinguishing them from kinematic enhancements. A bremsstrah…
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We propose to measure the photo-production cross section of $J/ψ$ near threshold, in search of the recently observed LHCb hidden-charm resonances $P_c$(4380) and $P_c$(4450) consistent with 'pentaquarks'. The observation of these resonances in photo-production will provide strong evidence of the true resonance nature of the LHCb states, distinguishing them from kinematic enhancements. A bremsstrahlung photon beam produced with an 11 GeV electron beam at CEBAF covers the energy range of $J/ψ$ production from the threshold photo-production energy of 8.2 GeV, to an energy beyond the presumed $P_c$(4450) resonance. The experiment will be carried out in Hall C at Jefferson Lab using a 50μA electron beam incident on a 9% copper radiator. The resulting photon beam passes through a 15 cm liquid hydrogen target, producing $J/ψ$ mesons through a diffractive process in the $t$-channel, or through a resonant process in the $s$- and $u$-channel. The decay $e^+e^-$ pair of the $J/ψ$ will be detected in coincidence using the two high-momentum spectrometers of Hall C. The spectrometer settings have been optimized to distinguish the resonant $s$- and $u$-channel production from the diffractive $t$-channel $J/ψ$ production. The $s$- and $u$-channel production of the charmed 5-quark resonance dominates the $t$-distribution at large $t$. The momentum and angular resolution of the spectrometers is sufficient to observe a clear resonance enhancement in the total cross section and $t$-distribution. We request a total of 11 days of beam time with 9 days to carry the main experiment and 2 days to acquire the needed $t$-channel elastic $J/ψ$ production data for a calibration measurement. This calibration measurement in itself will greatly enhance our knowledge of $t$-channel elastic $J/ψ$ production near threshold.
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Submitted 12 September, 2016; v1 submitted 2 September, 2016;
originally announced September 2016.