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The article reports on Thomas Jefferson National Accelerator Facility (Jefferson Lab) experiment E00-110, focusing on the photon electroproduction cross section in the deeply virtual Compton scattering (DVCS) regime and the valence quark region. It discusses the results of both helicity-dependent and helicity-independent cross sections. Topics include the kinematic settings of the photon electroproduction cross sections and the dominance of the twist-2 handbag amplitude.

We report the measurement of beam-target double spin asymmetries (ALT) in the inclusive production of identified hadrons, e + ³He↑→h+X, using a longitudinally polarized 5.9-GeV electron beam and a transversely polarized ³He target. Hadrons (π±,K±, and proton) were detected at 16° with an average momentum (Ph) = 2.35 GeV/c and a transverse momentum (pT) coverage from 0.60 to 0.68 GeV/c. Asymmetries from the ³He target were observed to be nonzero for π± production when the target was polarized transversely in the horizontal plane. The π+ and π- asymmetries have opposite signs, analogous to the behavior of ALT in semi-inclusive deep-inelastic scattering. [ABSTRACT FROM AUTHOR]

We present new experimental results for the ³He spin structure function g2 in the resonance region at Q² values between 1.2 and 3.0 (GeV/e)². Spin dependent moments of the neutron were extracted. Our main result, the inelastic contribution to the neutron d2 matrix element, was found to be small at (Q²) = 2.4 (GeV/c)² and in agreement with the lattice QCD calculation. The Burkhardt-Cottingham sum rule for ³He and the neutron was tested with the measured data and using the Wandzura-Wilczek relation for the low x unmeasured region. [ABSTRACT FROM AUTHOR]

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

Background: In the absence of accurate data on the free two-body hyperon-nucleon interaction, the spectra of hypernuclei provides information on the details of the effective hyperon-nucleon interaction. Purpose: To obtain a high-resolution binding-energy spectrum for the 9Be(e,e'K+)Λ9 Li reaction. Method: Electroproduction of the hypernucleus Λ9 Li has been studied for the first time with sub-MeV energy resolution in Hall A at Jefferson Lab on a 9Be target. In order to increase the counting rate and to provide unambiguous kaon identification, two superconducting septum magnets and a ring imaging Cherenkov detector were added to the Hall A standard equipment. Results: The cross section to low-lying states of Λ9 Li is concentrated within 3 MeV of the ground state and can be fit with four peaks. The positions of the doublets agree with theory while a disagreement could exist with respect to the relative strengths of the peaks in the doublets. The Λ separation energy, BΛ, of 8.36 ± 0.08 (stat.) ±0.08 (syst.) MeV was measured, in agreement with an earlier experiment. [ABSTRACT FROM AUTHOR]

Background: Measurements of forward exclusive meson production at different squared four-momenta of the exchanged virtual photon, Q², and at different four-momentum transfer, t, can be used to probe QCD's transition from meson-nucleon degrees of freedom at long distances to quark-gluon degrees of freedom at short scales. Ratios of separated response functions π- and π+ electroproduction are particularly informative. The ratio for transverse photons may allow this transition to be more easily observed, while the ratio for longitudinal photons provides a crucial verification of the assumed pole dominance, needed for reliable extraction of the pion form factor from electroproduction data. Purpose: We perform the first complete separation of the four unpolarized electromagnetic structure functions LITILTITT in forward, exclusive itπ+ electroproduction on deuterium above the dominant resonances. Method: Data were acquired with 2.6-5.2-GeV electron beams and the HMS + SOS spectrometers in Jefferson Lab Hall C at central Q² values of 0.6, 1.0, and 1.6 GeV² at W = 1.95 GeV, and Q2 = 2.45 GeV² at W = 2.22 GeV. There was significant coverage in ø and e, which allowed separation of oL π.LT.LT.T.T. Results: σL shows a clear signature of the pion pole, with a sharp rise at small - t . In contrast, aT is much flatter versus t. The longitudinal/transverse ratios evolve with Q² and t and at the highest Q² = 2.45 GeV² show a slight enhancement for π- production compared to π+. The π-/π- ratio for transverse photons exhibits only a small Q² dependence, following a nearly universal curve with t, with a steep transition to a value of about 0.25, consistent with .y-channel quark knockout. The σrT/σT ratio also drops rapidly with Q², qualitatively consistent with .v-channel helicity conservation. The π-/π+ ratio for longitudinal photons indicates a small isoscalar contamination at W = 1.95 GeV, consistent with what was observed in our earlier determination of the pion form factor at these kinematics. Conclusions: The separated cross sections are compared to a variety of theoretical models, which generally describe aL but have varying success with ar. Further theoretical input is required to provide a more profound insight into the relevant reaction mechanisms for longitudinal and transverse photons, such as whether the observed transverse ratio is indeed attributable to a transition from pion to quark knockout mechanisms and provide useful information regarding the twist-3 transversity generalized parton distribution, Hr. [ABSTRACT FROM AUTHOR]

An experiment to measure single-spin asymmetries of semi-inclusive production of charged pions in deepinelastic scattering on a transversely polarized3 He target was performed at Jefferson Laboratory in the kinematic region of 0.16 < x < 0.35 and 1.4 < Q² < 2.7 GeV². Pretzelosity asymmetries on ³He, which are expressed as the convolution of the *** transverse-momentum-dependent distribution functions and the Collins fragmentation functions in the leading order, were measured for the first time. Under the effective polarization approximation, we extracted the corresponding neutron asymmetries from the measured ³He asymmetries and cross-section ratios between the proton and ³He. Our results show that both π± on ³He and on neutron pretzelosity asymmetries are consistent with zero within experimental uncertainties. [ABSTRACT FROM AUTHOR]

We report the first measurement of the target-normal single-spin asymmetry in deep-inelastic scattering from the inclusive reaction 3He↑ (e, e')X on a polarized 3He gas target. Assuming time-reversal invariance, this asymmetry is strictly zero in the Born approximation but can be nonzero 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 < Q2 < 4.0 GeV2 and 0.16 < ϰ < 0.65. Neutron asymmetries were extracted using the effective nucleon polarization and measured proton-to-3He cross-section ratios. The measured neutron asymmetries are negative with an average value of (-1.09 ±0.38) x 10-2 for invariant mass W > 2 GeV, which is nonzero 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. [ABSTRACT FROM AUTHOR]

We studied simultaneously the 4He(e,e'p), 4He(e, e'p), and 4He(e,e'p) reactions at Q2 = 2(GeV/c)2 and ϰB > 1 , for an (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 (NN) force is expected to change from predominantly tensor to repulsive. The abundance of neutron-proton pairs 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. Our data are compared with calculations of two-nucleon momentum distributions in 4He and discussed in the context of probing the elusive repulsive component of the NN force. [ABSTRACT FROM AUTHOR]

The study of exclusive π± electroproduction on the nucleon, including separation of the various structure functions, is of interest for a number of reasons. The ratio RL = σπ-L/σπ+L is sensitive to isoscalar contamination to the dominant isovector pion exchange amplitude, which is the basis for the determination of the charged pion form factor from electroproduction data. A change in the value of RT = σπ-L/σπ+L from unity at small -t, to 1/4 at large -t , would suggest a transition from coupling to a (virtual) pion to coupling to individual quarks. Furthermore, the mentioned ratios may show an earlier approach to perturbative QCD than the individual cross sections. We have performed the first complete separation of the four unpolarized electromagnetic structure functions above the dominant resonances in forward, exclusive π± electroproduction on the deuteron at central Q2 values of 0.6, 1.0, 1.6 GeV2 at W = 1.95 GeV, and Q2 = 2.45 GeV2 at W = 2.22 GeV. Here, we present the L and T cross sections, with emphasis on RL and RT, and compare them with theoretical calculations. Results for the separated ratio RL indicate dominance of the pion-pole diagram at low -t, while results for RT are consistent with a transition between pion knockout and quark knockout mechanisms. [ABSTRACT FROM AUTHOR]

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

We report the first measurement of the double-spin asymmetry ALT for charged pion electroproduction in semi-inclusive deep-inelastic electron scattering on a transversely polarized 3He target. The kinematics focused on the valence quark region, 0.16 < x < 0.35 with 1.4 < Q2 < 2.7 GeV2. The corresponding neutron ALT asymmetries were extracted from the measured 3He asymmetries and proton over 3He cross section ratios using the effective polarization approximation. These new data probe the transverse momentum dependent parton distribution function gq1T and therefore provide access to quark spin-orbit correlations. Our results indicate a positive azimuthal asymmetry for π- production on 3He and the neutron, while our π+ asymmetries are consistent with zero. [ABSTRACT FROM AUTHOR]

The protons and neutrons in a nucleus can form strongly correlated nucleon pairs. Scattering experiments, in which a proton is knocked out of the nucleus with high-momentum transfer and high missing momentum, show that in carbon-12 the neutron-proton pairs are nearly 20 times as prevalent as proton-proton pairs and, by inference, neutron-neutron pairs. This difference between the types of pairs is due to the nature of the strong force and has implications for understanding cold dense nuclear systems such as neutron stars. [ABSTRACT FROM AUTHOR]

We report a precise measurement of the parity-violating (PV) asymmetry A&#95;{PV} in the elastic scattering of longitudinally polarized electrons from ^{48}Ca. We measure A&#95;{PV}=2668±106(stat)±40(syst) parts per billion, leading to an extraction of the neutral weak form factor F&#95;{W}(q=0.8733  fm^{-1})=0.1304±0.0052(stat)±0.0020(syst) and the charge minus the weak form factor F&#95;{ch}-F&#95;{W}=0.0277±0.0055. The resulting neutron skin thickness R&#95;{n}-R&#95;{p}=0.121±0.026(exp)±0.024(model)  fm is relatively thin yet consistent with many model calculations. The combined CREX and PREX results will have implications for future energy density functional calculations and on the density dependence of the symmetry energy of nuclear matter.

The internal structure of nucleons (protons and neutrons) remains one of the greatest outstanding problems in modern nuclear physics. By scattering high-energy electrons off a proton we are able to resolve its fundamental constituents and probe their momenta and positions. Here we investigate the dynamics of quarks and gluons inside nucleons using deeply virtual Compton scattering (DVCS)-a highly virtual photon scatters off the proton, which subsequently radiates a photon. DVCS interferes with the Bethe-Heitler (BH) process, where the photon is emitted by the electron rather than the proton. We report herein the full determination of the BH-DVCS interference by exploiting the distinct energy dependences of the DVCS and BH amplitudes. In the regime where the scattering is expected to occur off a single quark, measurements show an intriguing sensitivity to gluons, the carriers of the strong interaction.

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&#95;{L}/dt, dσ&#95;{T}/dt, dσ&#95;{LT}/dt, and dσ&#95;{TT}/dt are extracted as a function of the momentum transfer to the recoil system at Q^{2}=1.75  GeV^{2} and x&#95;{B}=0.36. The ed→edπ^{0} cross sections are found compatible with the small values expected from theoretical models. The en→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 generalized parton distributions 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.

We present deeply virtual π^{0} electroproduction cross-section measurements at x&#95;{B}=0.36 and three different Q^{2} values ranging from 1.5 to 2  GeV^{2}, obtained from Jefferson Lab Hall A experiment E07-007. The Rosenbluth technique is 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. Nonetheless, an indication of a nonzero longitudinal contribution is provided by the measured interference term σ&#95;{LT}. 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 in which the scattering amplitude includes convolution terms of chiral-odd (transversity) GPDs of the nucleon with the twist-3 pion distribution amplitude. This experiment, together with previous extensive unseparated measurements, provides strong support to the exciting idea that transversity GPDs can be accessed via neutral pion electroproduction in the high-Q^{2} regime.

We report on parity-violating asymmetries in the nucleon resonance region measured using inclusive inelastic scattering of 5-6 GeV longitudinally polarized electrons off an unpolarized deuterium target. These results are the first parity-violating asymmetry data in the resonance region beyond the Δ(1232). They provide a verification of quark-hadron duality-the equivalence of the quark- and hadron-based pictures of the nucleon-at the (10-15)% level in this electroweak observable, which is dominated by contributions from the nucleon electroweak γZ interference structure functions. In addition, the results provide constraints on nucleon resonance models relevant for calculating background corrections to elastic parity-violating electron scattering measurements.

We present new data for the polarization observables of the final state proton in the (1)H(γ,p)π(0) reaction. These data can be used to test predictions based on hadron helicity conservation and perturbative QCD. These data have both small statistical and systematic uncertainties and were obtained with beam energies between 1.8 and 5.6 GeV and for π(0) scattering angles larger than 75° in the center-of-mass frame. The data extend the polarization measurements database for neutral pion photoproduction up to E(γ)=5.6 GeV. The results show a nonzero induced polarization above the resonance region. The polarization transfer components vary rapidly with the photon energy and π(0) scattering angle in the center-of-mass frame. This indicates that hadron helicity conservation does not hold and that the perturbative QCD limit is still not reached in the energy regime of this experiment.

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  GeV2 and beam energy E(b) = 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) + 0.517G(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.

Intensive theoretical and experimental efforts over the past decade have aimed at explaining the discrepancy between data for the proton electric to magnetic form factor ratio, G(E)/G(M), obtained separately from cross section and polarization transfer measurements. One possible explanation for this difference is a two-photon-exchange contribution. In an effort to search for effects beyond the one-photon-exchange or Born approximation, we report measurements of polarization transfer observables in the elastic H(e[over →],e(')p[over →]) reaction for three different beam energies at a Q(2)=2.5  GeV(2), spanning a wide range of the kinematic parameter ε. The ratio R, which equals μ(p)G(E)/G(M) in the Born approximation, is found to be independent of ε at the 1.5% level. The ε dependence of the longitudinal polarization transfer component P(ℓ) shows an enhancement of (2.3±0.6)% relative to the Born approximation at large ε., (© 2011 American Physical Society)

The electric form factor of the neutron was determined from studies of the reaction 3He(e,e'n)pp in quasielastic kinematics in Hall A at Jefferson Lab. Longitudinally polarized electrons were scattered off a polarized target in which the nuclear polarization was oriented perpendicular to the momentum transfer. The scattered electrons were detected in a magnetic spectrometer in coincidence with neutrons that were registered in a large-solid-angle detector. More than doubling the Q2 range over which it is known, we find G(E)(n)=0.0236±0.0017(stat)±0.0026(syst), 0.0208±0.0024±0.0019, and 0.0147±0.0020±0.0014 for Q(2)=1.72, 2.48, and 3.41 GeV2, respectively.

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

An experimental study of the (16)O(e,e'K(+))(Lambda)(16)N reaction has been performed at Jefferson Lab. A thin film of falling water was used as a target. This permitted a simultaneous measurement of the p(e,e'K(+))Lambda, Sigma(0) exclusive reactions and a precise calibration of the energy scale. A ground-state binding energy of 13.76+/-0.16 MeV was obtained for (Lambda)(16)N with better precision than previous measurements on the mirror hypernucleus (Lambda)(16)O. Precise energies have been determined for peaks arising from a Lambda in s and p orbits coupled to the p(1/2) and p(3/2) hole states of the (15)N core nucleus.

The present experiment exploits the interference between the deeply virtual Compton scattering (DVCS) and the Bethe-Heitler processes to extract the imaginary part of DVCS amplitudes on the neutron and on the deuteron from the helicity-dependent D(e,e'gamma)X cross section measured at Q2=1.9 GeV2 and xB=0.36. We extract a linear combination of generalized parton distributions (GPDs) particularly sensitive to E&#95;{q}, the least constrained GPD. A model dependent constraint on the contribution of the up and down quarks to the nucleon spin is deduced.