This Article is brought to you for free and open access by the Physics at ODU Digital Commons. It has been accepted for inclusion in Physics Faculty Publications by an authorized administrator of ODU Digital Commons. For more information, please contact digitalcommons@odu.edu. Repository Citation CLAS Collaboration; Amaryan, M. J.; Careccia, S. L.; Dodge, G. E.; Hyde, C. E.; Kuhn, S. E.; Mayer, M.; Nepali, C. S.; Niroula, M. R.; Seraydaryan, H.; Tkachenko, S.; Weinstein, L.B.; and Zhang, J., "Photodisintegration of 4HE into p+t" (2009). Physics Faculty Publications. 353. https://digitalcommons.odu.edu/physics_fac_pubs/353

Using data from the recent BONuS experiment at Jefferson Lab, which utilized a novel spectator tagging technique to extract the inclusive electron-free neutron scattering cross section, we obtain the first direct observation of quark-hadron duality in the neutron F2 structure function. In addition, the data are used to reconstruct the lowest few (N = 2, 4 and 6) moments of F2 in the three prominent nucleon resonance regions, as well as the moments integrated over the entire resonance region. Comparison with moments computed from global parametrizations of parton distribution functions suggest that quark--hadron duality holds locally for the neutron in the second and third resonance regions down to Q2 ≈ 1 GeV2, with violations possibly up to 20% observed in the first resonance region.

We present the final results for the deuteron spin structure functions obtained from the full data set collected with Jefferson Lab's CLAS in 2000-2001. Polarized electrons with energies of 1.6, 2.5, 4.2 and 5.8 GeV were scattered from deuteron (^15ND_3) targets, dynamically polarized along the beam direction, and detected with CLAS. From the measured double spin asymmetry, the virtual photon absorption asymmetry A_1^d and the polarized structure function g_1^d were extracted over a wide kinematic range (0.05 GeV^2 < Q^2 < 5 GeV^2 and 0.9 GeV < W < 3 GeV). We use an unfolding procedure and a parametrization of the corresponding proton results to extract from these data the polarized structure functions A_1^n and g_1^n of the (bound) neutron, which are so far unknown in the resonance region, W < 2 GeV. We compare our final results, including several moments of the deuteron and neutron spin structure functions, with various theoretical models and expectations as well as parametrizations of the world data. The unprecedented precision and dense kinematic coverage of these data can aid in future extractions of polarized parton distributions, tests of perturbative QCD predictions for the quark polarization at large x, a better understanding of quark-hadron duality, and more precise values for higher-twist matrix elements in the framework of the Operator Product Expansion.

Unpolarized and beam-polarized fourfold cross sections (d^{4}σ/dQ^{2}dx_{B}dtdϕ) for the ep→e^{'}p^{'}γ reaction were measured using the CLAS detector and the 5.75-GeV polarized electron beam of the Jefferson Lab accelerator, for 110 (Q^{2},x_{B},t) bins over the widest phase space ever explored in the valence-quark region. Several models of generalized parton distributions (GPDs) describe the data well at most of our kinematics. This increases our confidence that we understand the GPD H, expected to be the dominant contributor to these observables. Through a leading-twist extraction of Compton form factors, these results support the model predictions of a larger nucleon size at lower quark-momentum fraction x_{B}.

We determined the structure function ratio R-EMC(d) = F-2(d)/(F-2(n) + F-2(p)) from recently published F-2(n)/F-2(d) data taken by the BONuS experiment using CLAS at Jefferson Lab. This ratio deviates from unity, with a slope dR(EMC)(d)/dx=-0.10 +/- 0.05 in the range of Bjorken x from 0.35 to 0.7, for invariant mass W > 1.4 GeV and Q(2) > 1GeV(2). The observed EMC effect for these kinematics is consistent with conventional nuclear physics models that include off-shell corrections, as well as with empirical analyses that find the EMC effect proportional to the probability of short-range nucleon-nucleon correlations

Much less is known about neutron structure than that of the proton due to the absence of free neutron targets. Neutron information is usually extracted from data on nuclear targets such as deuterium, requiring corrections for nuclear binding and nucleon off-shell effects. These corrections are model dependent and have significant uncertainties, especially for large values of the Bjorken scaling variable x. The Barely Off-shell Nucleon Structure (BONuS) experiment at Jefferson Lab measured the inelastic electron deuteron scattering cross section, tagging spectator protons in coincidence with the scattered electrons. This method reduces nuclear binding uncertainties significantly and has allowed for the first time a (nearly) model independent extraction of the neutron structure function. A novel compact radial time projection chamber was built to detect protons with momentum between 70 and 150 MeV/c. For the extraction of the free neutron structure function F_2n, spectator protons at backward angle and with momenta below 100 MeV/c were selected, ensuring that the scattering took place on a nearly free neutron. The scattered electrons were detected with Jefferson Lab's CLAS spectrometer. The extracted neutron structure function F_2n and its ratio to the deuteron structure function F_2d are presented in both the resonance and deep inelastic regions. The dependence of the cross section on the spectator proton momentum and angle is investigated, and tests of the spectator mechanism for different kinematics are performed. Our data set can be used to study neutron resonance excitations, test quark hadron duality in the neutron, develop more precise parametrizations of structure functions, as well as investigate binding effects (including possible mechanisms for the nuclear EMC effect) and provide a first glimpse of the asymptotic behavior of d/u as x goes to 1.

We report the first measurement of the photoproduction cross section of the $\phi$ meson in its neutral decay mode in the reaction $\gamma p \to p\phi(K_SK_L)$. The experiment was performed with a tagged photon beam of energy $1.6 \le E_\gamma \le 3.6$ GeV incident on a liquid hydrogen target of the CLAS spectrometer at the Thomas Jefferson National Accelerator Facility. The $p \phi$ final state is identified via reconstruction of $K_S$ in the invariant mass of two oppositely charged pions and by requiring the missing particle in the reaction $\gamma p \to p K_S X$ to be $K_L$. The presented results significantly enlarge the existing data on $\phi$-photoproduction. These data, combined with the data from the charged decay mode, will help to constrain different mechanisms of $\phi$ photoproduction.

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

Received 27 January 2014DOI:https://doi.org/10.1103/PhysRevC.89.029901©2014 American Physical Society

We propose to perform the first measurements of the spin-dependent EMC effect utilizing CLAS12 in Hall B with 11 GeV polarized electrons and polarized nuclear targets. Our target of choice is Li (in the form of dynamically polarized LiD) in which a highly polarized proton is embedded in the nuclear medium. Simultaneously, we will also measure the double spin asymmetry on the proton with a LiH target, to minimize systematic uncertainties. The experiment will obtain the double spin asymmetry A Li || ≈ g Li 1 /F Li 1 from the measurement on LiD, after correcting for the small contribution from other polarized species (D) and the beam and target polarization as well as the dilution by unpolarized target components. Using the simultaneous measurement on LiH, we can form the ratio of the double spin asymmetries as well as the cross section differences directly (with many systematic uncertainties canceling), both of which contain direct information on any medium effect on spin structure functions and asymmetries. Together with the unpolarized structure function (to be measured in Hall C), we can also extract g Li 1 and, using a sophisticated modern wave function model, finally the “in-medium” spin structure function function g p|Li 1 for a proton bound in LiD. We will cover a kinematic range of 1 < Q < 15 GeV and 0.06 < x < 0.8. These data will provide new constraints on models for the EMC effect, some of which predict that medium modifications of quark distributions depend strongly on the quark helicities. We request 50 days of 11 GeV beam on the longitudinal polarized target and 5 additional days for auxiliary measurements.

The inclusive polarized structure functions of the proton and deuteron, g(1)(p) and g(1)(d) , were measured with high statistical precision using polarized 6 GeV electrons incident on a polarized ammonia target in Hall B at Jefferson Laboratory. Electrons scattered at laboratory angles between 18 and 45 degrees were detected using the CEBAF Large Acceptance Spectrometer (CLAS). For the usual deep inelastic region kinematics, Q(2) > 1 GeV2 and the final-state invariant mass W > 2 GeV, the ratio of polarized to unpolarized structure functions g(1)/F-1 is found to be nearly independent of Q(2) at fixed x. Significant resonant structure is apparent at values of W up to 2.3 GeV. In the framework of perturbative quantum chromodynamics, the high-W results can be used to better constrain the polarization of quarks and gluons in the nucleon, as well as high-twist contributions.

This Article is brought to you for free and open access by the Physics at ODU Digital Commons. It has been accepted for inclusion in Physics Faculty Publications by an authorized administrator of ODU Digital Commons. For more information, please contact digitalcommons@odu.edu. Repository Citation Baghdasaryan, H.; Weinstein, L. B.; Laget, J. M.; Adhikari, K. P.; Aghasyan, M.; Amaryan, M. J.; Anghinolfi, M.; Ball, J.; Battaglieri, M.; Biselli, A. S.; Dodge, G.; Hyde, C. E.; Kuhn, S. E.; and Seraydaryan, H., "Comparison of Forward and Backward pp Pair Knockout in 3He(e,e'pp)n" (2012). Physics Faculty Publications. 86. https://digitalcommons.odu.edu/physics_fac_pubs/86