Search for Effects Beyond the Born Approximation in Polarization Transfer Observables ine→pElastic Scattering

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 (TPEX) 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 $$H(\vec{e},e'\vec{p})$$ reaction for three different beam energies at a fixed squared momentum transfer $Q^2 = 2.5$ GeV$^2$, spanning a wide range of the virtual photon p…

Polarization observables in deuteron photodisintegration below 360 MeV

High precision measurements of induced and transferred recoil proton polarization in d(polarized gamma, polarized p})n have been performed for photon energies of 277--357 MeV and theta_cm = 20 degrees -- 120 degrees. The measurements were motivated by a longstanding discrepancy between meson-baryon model calculations and data at higher energies. At the low energies of this experiment, theory continues to fail to reproduce the data, indicating that either something is missing in the calculations and/or there is a problem with the accuracy of the nucleon-nucleon potential being used.

Virtual Compton scattering and the generalized polarizabilities of the proton atQ2=0.92and 1.76 GeV2

Virtual Compton Scattering (VCS) on the proton has been studied at Jefferson Lab using the exclusive photon electroproduction reaction (e p --> e p gamma). This paper gives a detailed account of the analysis which has led to the determination of the structure functions P{sub LL}-P{sub TT}/epsilon and P{sub LT}, and the electric and magnetic generalized polarizabilities (GPs) alpha{sub E}(Q{sup 2}) and beta{sub M}(Q{sup 2}) at values of the four-momentum transfer squared Q{sup 2} = 0.92 and 1.76 GeV{sup 2}. These data, together with the results of VCS experiments at lower momenta, help building a coherent picture of the electric and magnetic GPs of the proton over the full measured Q{sup 2}-…

Spectroscopy of A=9 hyperlithium with the (e,e′K+) reaction

High resolution spectroscopic study ofBeΛ10

Spectroscopy of a Be-10(Lambda) hypernucleus was carried out at JLab Hall C using the (e, e' K+) reaction. A new magnetic spectrometer system (SPL+ HES+ HKS), specifically designed for high resolution hypernuclear spectroscopy, was used to obtain an energy spectrum with a resolution of similar to 0.78 MeV (FWHM). The well-calibrated spectrometer system of the present experiment using p(e, e' K+)Lambda, Sigma(0) reactions allowed us to determine the energy levels; and the binding energy of the ground-state peak (mixture of 1(-) and 2(-) states) was found to be B-Lambda = 8.55 +/- 0.07(stat.) +/- 0.11(sys.) MeV. The result indicates that the ground-state energy is shallower than that of an em…

Experiments with the High Resolution Kaon Spectrometer at JLab Hall C and the new spectroscopy ofΛ12Bhypernuclei

Since the pioneering experiment E89-009 studying hypernuclear spectroscopy using the (e, e’K+) reaction was completed, two additional experiments, E01-011 and E05-115, were performed at Jefferson Lab. These later experiments used a modified experimental design, the "tilt method", to dramatically suppress the large electromagnetic background, and allowed for a substantial increase in luminosity. Additionally, a new kaon spectrometer, HKS (E01-011), a new electron spectrometer, HES, and a new splitting magnet (E05-115) were added to produce new data sets of precision, high-resolution hypernuclear spectroscopy. All three experiments obtained a spectrum for 12B-Lambda, which is the most charact…

Spectroscopy of the neutron-rich hypernucleusHeΛ7from electron scattering

The missing mass spectroscopy of the HeΛ7 hypernucleus was performed using the Li7(e, e ′K+)HeΛ7 reaction at the Thomas Jefferson National Accelerator Facility Hall C. The Λ- binding energy of the ground-state (1/2+) was determined with a smaller error than that of the previous measurement, being BΛ=5.55±0.10stat.±0.11sys.MeV. The experiment also provided new insight into charge symmetry breaking in p-shell hypernuclear systems. Finally, a peak at BΛ=3.65±0.20stat. ±0.11sys.MeV was observed and assigned as a mixture of 3/2+ and 5/2+ states, confirming the "gluelike" behavior of Λ, which makes an unstable state in He6 stable against neutron emission.

Backward electroproduction ofπ0mesons on protons in the region of nucleon resonances at four momentum transfer squaredQ2=1.0GeV2

Exclusive electroproduction of pi{sup 0} mesons on protons in the backward hemisphere has been studied at Q2 = 1.0 GeV2 by detecting protons in the forward direction in coincidence with scattered electrons from the 4 GeV electron beam in Jefferson Lab's Hall A. The data span the range of the total (gamma*p) center-of-mass energy W from the pion production threshold to W = 2.0 GeV. The differential cross sections sigma{sub T} + epsilon sigma{sub L}, sigma{sub TL}, and sigma{sub TT} were separated from the azimuthal distribution and are presented together with the MAID and SAID parameterizations.

Virtual Compton Scattering and Neutral Pion Electroproduction in the Resonance Region up to the Deep Inelastic Region at Backward Angles

We have made the first measurements of the virtual Compton scattering (VCS) process via the H$(e,e'p)\gamma$ exclusive reaction in the nucleon resonance region, at backward angles. Results are presented for the $W$-dependence at fixed $Q^2=1$ GeV$^2$, and for the $Q^2$-dependence at fixed $W$ near 1.5 GeV. The VCS data show resonant structures in the first and second resonance regions. The observed $Q^2$-dependence is smooth. The measured ratio of H$(e,e'p)\gamma$ to H$(e,e'p)\pi^0$ cross sections emphasizes the different sensitivity of these two reactions to the various nucleon resonances. Finally, when compared to Real Compton Scattering (RCS) at high energy and large angles, our VCS data…

Direct measurements of the lifetime of medium-heavy hypernuclei

Abstract The lifetime of a Λ particle embedded in a nucleus (hypernucleus) decreases from that of free Λ decay mainly due to the opening of the Λ N → N N weak decay channel. However, it is generally believed that the lifetime of a hypernucleus attains a constant value (saturation) for medium to heavy hypernuclear masses, yet this hypothesis has been difficult to verify. This paper presents a direct measurement of the lifetime of medium-heavy hypernuclei that were hyper-fragments produced by fission or break-up from heavy hypernuclei initially produced with a 2.34 GeV photon-beam incident on thin Fe, Cu, Ag, and Bi target foils. For each event, fragments were detected in coincident pairs by …

High Resolution Λ Hypernuclear Spectroscopy with Electron Beams

T. Gogami1 ∗, P. Achenbach2, A. Ahmidouch3, I. Albayrak4, D. Androic5, A. Asaturyan6, R. Asaturyan6, O. Ates4, P. Baturin7, R. Badui7, W. Boeglin7, J. Bono7, E. Brash8, P. Carter8, C. Chen4, A. Chiba1, E. Christy4, S. Danagoulian3, R. De Leo10, D. Doi1, M. Elaasar11, R. Ent9, Y. Fujii1, M. Fujita1, M. Furic5, M. Gabrielyan7, L. Gan12, F. Garibaldi13, D. Gaskell9, A. Gasparian3, O. Hashimoto1, T. Horn9, B. Hu14, Ed. V. Hungerford21, M. Jones9, H. Kanda1, M. Kaneta1, S. Kato19, M. Kawai1, D. Kawama1, H. Khanal7, M. Kohl4, A. Liyanage4, W. Luo14, K. Maeda1, A. Margaryan6, P. Markowitz7, T. Maruta1, A. Matsumura1, V. Maxwell7, A. Mkrtchyan6, H. Mkrtchyan6, S. Nagao1, S. N. Nakamura1, A. Narayan…