Plans for Hadronic Structure Studies at J-PARC

Hadron-physics projects at J-PARC are explained. The J-PARC is the most-intense hadron-beam facility in the multi-GeV high-energy region. By using secondary beams of kaons, pions, and others as well as the primary-beam proton, various hadron projects are planned. First, some of approved experiments are introduced on strangeness hadron physics and hadron-mass modifications in nuclear medium. Second, future possibilities are discussed on hadron-structure physics, including structure functions of hadrons, spin physics, and high-energy hadron reactions in nuclear medium. The second part is discussed in more details because this is an article in the hadron-structure session.Comment: 10 pages, LaTeX, 20 eps files, to be published in Journal of Physics: Conference Series (JPCS), Proceedings of the 24th International Nuclear Physics Conference (INPC 2010), Vancouver, Canada, July 4 - 9, 201

Properties of the Resonance Lambda(1520) as seen in the Forward Electroproduction at JLab Hall A

High-resolution spectrometer measurements of the reaction H(e,e' K+)X at small Q2 are used to extract the mass and width of the Lambda(1520). We investigate dependence of the resonance parameters on different parametrizations of the background and the resonance peak itself. Our final values for the Breit-Wigner parameters are M=1520.4+-0.6(stat)+-1.5(syst) MeV and Gamma=18.6+-1.9(stat)+-1(syst) MeV. The width appears to be more sensitive to the assumptions than the mass. We also estimate, for the first time, the pole position for this resonance and find that both the pole mass and width seem to be smaller than their Breit-Wigner values.Comment: 4 pages, 1 figure, to appear in the proceedings of MENU 201

Performance of the Two Aerogel Cherenkov Detectors of the JLab Hall A Hadron Spectrometer

We report on the design and commissioning of two silica aerogel Cherenkov detectors with different refractive indices. In particular, extraordinary performance in terms of the number of detected photoelectrons was achieved through an appropriate choice of PMT type and reflector, along with some design considerations. After four years of operation, the number of detected photoelectrons was found to be noticeably reduced in both detectors as a result of contamination, yellowing, of the aerogel material. Along with the details of the set-up, we illustrate the characteristics of the detectors during different time periods and the probable causes of the contamination. In particular we show that the replacement of the contaminated aerogel and parts of the reflecting material has almost restored the initial performance of the detectors.Comment: 18 pages, 9 Figures, 4 Tables, 44 Reference

Electroexcitation of the Δ+ (1232) at Low Momentum Transfer

We report on new p(e, e\u27 p)π°. measurements at the Δ+(1232) resonance at the low momentum transfer region, where the mesonic cloud dynamics is predicted to be dominant and rapidly changing, offering a test bed for chiral effective field theory calculations. The new data explore the Q2 dependence of the resonant quadrupole amplitudes and for the first time indicate that the Electric and the Coulomb quadrupole amplitudes converge as Q2 -\u3e 0. The measurements of the Coulomb quadrupole amplitude have been extended to the lowest momentum transfer ever reached, and suggest that more than half of its magnitude is attributed to the mesonic cloud in this region. The new data 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 measurements indicate that improvement is required to the theoretical calculations and provide valuable input that will allow their refinements

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

We studied simultaneously the 4He(e,e′p), 4He (e,e′pp), and 4He( e,e′pn) reactions at Q2 = 2(GeV/c)2 and xB \u3e 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

Unique Electron Polarimeter Analyzing Power Comparison and Precision Spin-Based Energy Measurement

Precision measurements of the relative analyzing powers of five electron beam polarimeters, based on Compton, Moller, and Mott scattering, have been performed using the CEBAF accelerator at the Thomas Jefferson National Accelerator Facility ( Jefferson Laboratory). A Wien filter in the 100 keV beam line of the injector was used to vary the electron spin orientation exiting the injector. High statistical precision measurements of the scattering asymmetry as a function of the spin orientation were made with each polarimeter. Since each polarimeter receives beam with the same magnitude of polarization, these asymmetry measurements permit a high statistical precision comparison of the relative analyzing powers of the five polarimeters. This is the first time a precise comparison of the analyzing powers of Compton, Moller, and Mott scattering polarimeters has been made. Statistically significant disagreements among the values of the beam polarization calculated from the asymmetry measurements made with each polarimeter reveal either errors in the values of the analyzing power or failure to correctly include all systematic effects. The measurements reported here represent a first step toward understanding the systematic effects of these electron polarimeters. Such studies are necessary to realize high absolute accuracy (ca. 1%) electron polarization measurements, as required for some parity violation measurements planned at Jefferson Laboratory. Finally, a comparison of the value of the spin orientation exiting the injector that provides maximum longitudinal polarization in each experimental hall leads to an independent and very precise ( better than 10-4) absolute measurement of the final electron beam energy

First Measurement of the Ar (e,e\u27)X Cross Section at Jefferson Laboratory

The success of the ambitious programs of both long- and short-baseline neutrino-oscillation experiments employing liquid-argon time-projection chambers will greatly rely on the precision with which the weak response of the argon nucleus can be estimated. In the E12-14-012 experiment at Jefferson Lab Hall A, we studied the properties of the argon nucleus by scattering a high-quality electron beam off a high-pressure gaseous argon target. Here, we present the measured 40Ar(e,e\u27) double differential cross section at incident electron energy E=2.222 GeV and scattering angle Θ = 15.54°. The data cover a broad range of energy transfers, where quasielastic scattering and delta production are the dominant reaction mechanisms. The result for argon is compared to our previously reported cross sections for titanium and carbon, obtained in the same kinematical setup