Generalized Contact Formalism Analysis of the ⁴He(e,e′pN) Reaction

Measurements of short-range correlations in exclusive 4He (e , e ′ p N) reactions are analyzed using the Generalized Contact Formalism (GCF). We consider both instant-form and light-cone formulations with both the AV18 and local N2LO(1.0) nucleon-nucleon (NN) potentials. We find that kinematic distributions, such as the reconstructed pair opening angle, recoil neutron momentum distribution, and pair center of mass motion, as well as the measured missing energy, missing mass distributions, are all well reproduced by GCF calculations. The missing momentum dependence of the measured 4He (e , e ′ p N) /4He (e , e ′ p) cross-section ratios, sensitive to nature of the NN interaction at short-distacnes, are also well reproduced by GCF calculations using either interaction and formulation. This gives credence to the GCF scale-separated factorized description of the short-distance many-body nuclear wave-function

Update of High Resolution (e,e'K^+) Hypernuclear Spectroscopy at Jefferson Lab's Hall A

Updated results of the experiment E94-107 hypernuclear spectroscopy in Hall A of the Thomas Jefferson National Accelerator Facility (Jefferson Lab), are presented. The experiment provides high resolution spectra of excitation energy for 12B_\Lambda, 16N_\Lambda, and 9Li_\Lambda hypernuclei obtained by electroproduction of strangeness. A new theoretical calculation for 12B_\Lambda, final results for 16N_\Lambda, and discussion of the preliminary results of 9Li_\Lambda are reported.Comment: 8 pages, 5 figures, submitted to the proceedings of Hyp-X Conferenc

Properties of the Lambda(1520) Resonance from High-Precision Electroproduction Data

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 the influence of various assumptions used in the extraction. The width appears to be more sensitive to the assumptions than the mass. To reach a width uncertainty about 1 MeV or better, one needs to know the structure of the non-resonant background. Based on the new Jefferson Lab Hall A data, our final values for the Breit-Wigner parameters are M = 1520.4 +- 0.6 (stat) +- 1.5 (syst) MeV, Gamma = 18.6 +- 1.9 (stat) +- 1 (syst) MeV. For the first time, we also estimate the pole position for this resonance and find that both the pole mass and width seem to be smaller than the Breit-Wigner values.Comment: 7 pages, 3 figures; corresponds to the published versio

Hard probes of short-range nucleon-nucleon correlations

One of the primary goals of nuclear physics is providing a complete description of the structure of atomic nuclei. While mean-field calculations provide detailed information on the nuclear shell structure for a wide range of nuclei, they do not capture the complete structure of nuclei, in particular the impact of small, dense structures in nuclei. The strong, short-range component of the nucleon-nucleon potential yields hard interactions between nucleons which are close together, generating a high-momentum tail to the nucleon momentum distribution, with momenta well in excess of the Fermi momentum. This high-momentum component of the nuclear wave-function is one of the most poorly understood parts of nuclear structure. Utilizing high-energy probes, we can isolate scattering from high-momentum nucleons, and use these measurements to examine the structure and impact of short-range nucleon-nucleon correlations. Over the last decade we have moved from looking for evidence of such short-range structures to mapping out their strength in nuclei and examining their isospin structure. This has been made possible by high-luminosity and high-energy accelerators, coupled with an improved understanding of the reaction mechanism issues involved in studying these structures. We review the general issues related to short-range correlations, survey recent experiments aimed at probing these short-range structures, and lay out future possibilities to further these studies.Comment: Review article to appear in Prog.Part.Nucl.Phys. 77 pages, 33 figure

Cross Section Measurements of Charged Pion Photoproduction in Hydrogen and Deuterium from 1.1 to 5.5 GeV

The differential cross section for the gamma +n --> pi- + p and the gamma + p --> pi+ n processes were measured at Jefferson Lab. The photon energies ranged from 1.1 to 5.5 GeV, corresponding to center-of-mass energies from 1.7 to 3.4 GeV. The pion center-of-mass angles varied from 50 degree to 110 degree. The pi- and pi+ photoproduction data both exhibit a global scaling behavior at high energies and high transverse momenta, consistent with the constituent counting rule prediction and the existing pi+ data. The data suggest possible substructure of the scaling behavior, which might be oscillations around the scaling value. The data show an enhancement in the scaled cross section at center-of-mass energy near 2.2 GeV. The differential cross section ratios at high energies and high transverse momenta can be described by calculations based on one-hard-gluon-exchange diagrams.Comment: 18 pages, 19 figure

Probing the high momentum component of the deuteron at high Q^2

The d(e,e'p) cross section at a momentum transfer of 3.5 (GeV/c)^2 was measured over a kinematical range that made it possible to study this reaction for a set of fixed missing momenta as a function of the neutron recoil angle theta_nq and to extract missing momentum distributions for fixed values of theta_nq up to 0.55 GeV/c. In the region of 35 (deg) <= theta_nq <= 45 (deg) recent calculations, which predict that final state interactions are small, agree reasonably well with the experimental data. Therefore these experimental reduced cross sections provide direct access to the high momentum component of the deuteron momentum distribution in exclusive deuteron electro-disintegration.Comment: 5 pages, 2 figure

The Charge Form Factor of the Neutron from the Reaction \pol{2H}(\pol{e},e'n)p

We report on the first measurement of spin-correlation parameters in quasifree electron scattering from vector-polarized deuterium. Polarized electrons were injected into an electron storage ring at a beam energy of 720~MeV. A Siberian snake was employed to preserve longitudinal polarization at the interaction point. Vector-polarized deuterium was produced by an atomic beam source and injected into an open-ended cylindrical cell, internal to the electron storage ring. The spin correlation parameter A^V_{ed} was measured for the reaction \pol{2H}(\pol{e},e'n)p at a four-momentum transfer squared of 0.21 (GeV/c)^2 from which a value for the charge form factor of the neutron was extracted.Comment: 4 pages, 5 file

Hard Photodisintegration of a Proton Pair

We present a study of high energy photodisintegration of proton-pairs through the gamma + 3He -> p+p+n channel. Photon energies from 0.8 to 4.7 GeV were used in kinematics corresponding to a proton pair with high relative momentum and a neutron nearly at rest. The s-11 scaling of the cross section, as predicted by the constituent counting rule for two nucleon photodisintegration, was observed for the first time. The onset of the scaling is at a higher energy and the cross section is significantly lower than for deuteron (pn pair) photodisintegration. For photon energies below the scaling region, the scaled cross section was found to present a strong energy-dependent structure not observed in deuteron photodisintegration.Comment: 7 pages, 3 figures, for submission to Phys. Lett.

Exclusive Neutral Pion Electroproduction in the Deeply Virtual Regime

We present measurements of the ep->ep pi^0 cross section extracted at two values of four-momentum transfer Q^2=1.9 GeV^2 and Q^2=2.3 GeV^2 at Jefferson Lab Hall A. The kinematic range allows to study the evolution of the extracted hadronic tensor as a function of Q^2 and W. Results will be confronted with Regge inspired calculations and GPD predictions. An intepretation of our data within the framework of semi-inclusive deep inelastic scattering has also been attempted