Two nucleon momentum distributions mea sured in 3He(e; e0pp)n

We have measured the 3He(e,e′pp)n reaction at 2.2 GeV over a wide kinematic range. The kinetic energy distribution for “fast” nucleons (p\u3e250   MeV/c) peaks where two nucleons each have 20% or less, and the third nucleon has most of the transferred energy. These fast pp and pn pairs are back to back with little momentum along the three-momentum transfer, indicating that they are spectators. Calculations by Sargsian and by Laget also indicate that we have measured distorted two-nucleon momentum distributions by striking one nucleon and detecting the spectator correlated pair

Electron scattering from high-momentum neutrons in deuterium

We report results from an experiment measuring the semiinclusive reaction 2H(e,e′ps) in which the proton ps is moving at a large angle relative to the momentum transfer. If we assume that the proton was a spectator to the reaction taking place on the neutron in deuterium, the initial state of that neutron can be inferred. This method, known as spectator tagging, can be used to study electron scattering from high-momentum (off-shell) neutrons in deuterium. The data were taken with a 5.765 GeV electron beam on a deuterium target in Jefferson Laboratory\u27s Hall B, using the CEBAF large acceptance spectrometer. A reduced cross section was extracted for different values of final state missing mass W+, backward proton momentum p→s, and momentum transfer Q2. The data are compared to a simple plane wave impulse approximation (PWIA) spectator model. A strong enhancement in the data observed at transverse kinematics is not reproduced by the PWIA model. This enhancement can likely be associated with the contribution of final state interactions (FSI) that were not incorporated into the model. Within the framework of the simple spectator model, a “bound neutron structure function” Feff2n was extracted as a function of W+ and the scaling variable x∗ at extreme backward kinematics, where the effects of FSI appear to be smaller. For ps\u3e0.4GeV/c, where the neutron is far off-shell, the model overestimates the value of Feff2n in the region of x∗ between 0.25 and 0.6. A dependence of the bound neutron structure function on the neutron\u27s “off-shell-ness” is one possible effect that can cause the observed deviation

Proton Source Size Measurements in the eA→e′ppX Reaction

Two-proton correlations at small relative momentum q were studied in the eA(3He,4He,C,Fe)→e′ppX reaction at E0=4.46  GeV using the CLAS detector at Jefferson Lab. The enhancement of the correlation function at small q was found to be in accordance with theoretical expectations. Sizes of the emission region were extracted, and proved to be dependent on A and on the proton momentum. The size of the two-proton emission region for He was measured in eA reactions for the first time

Search for baryon-number and lepton-number violating decays of Lambda hyperons using the CLAS detector at Jefferson Laboratory

We present a search for ten baryon number violating decay modes of. hyperons using the CLAS detector at Jefferson Laboratory. Nine of these decay modes result in a single meson and single lepton in the final state (Lambda - \u3e ml) and conserve either the sum or the difference of baryon and lepton number (B +/- L). The tenth decay mode (Lambda - \u3e (p) over bar pi(+)) represents a difference in baryon number of two units and no difference in lepton number. We observe no significant signal and set upper limits on the branching fractions of these reactions in the range (4-200) x 10(-7) at the 90% confidence level

Longitudinal Target-Spin Asymmetries for Deeply Virtual Compton Scattering

A measurement of the electroproduction of photons off protons in the deeply inelastic regime was performed at Jefferson Lab using a nearly 6 GeV electron beam, a longitudinally polarized proton target, and the CEBAF Large Acceptance Spectrometer. Target-spin asymmetries for e p → e\u27p\u27ɣ events, which arise from the interference of the deeply virtual Compton scattering and the Bethe-Heitler processes, were extracted over the widest kinematics in Q2, xB, t, and ɸ, for 166 four-dimensional bins. In the framework of generalized parton distributions, at leading twist the t dependence of these asymmetries provides insight into the spatial distribution of the axial charge of the proton, which appears to be concentrated in its center. These results also bring important and necessary constraints for the existing parametrizations of chiral-even generalized parton distributions

G0^0 Electronics and Data Acquisition (Forward-Angle Measurements)

The G$^0$ parity-violation experiment at Jefferson Lab (Newport News, VA) is designed to determine the contribution of strange/anti-strange quark pairs to the intrinsic properties of the proton. In the forward-angle part of the experiment, the asymmetry in the cross section was measured for $\vec{e}p$ elastic scattering by counting the recoil protons corresponding to the two beam-helicity states. Due to the high accuracy required on the asymmetry, the G$^0$ experiment was based on a custom experimental setup with its own associated electronics and data acquisition (DAQ) system. Highly specialized time-encoding electronics provided time-of-flight spectra for each detector for each helicity state. More conventional electronics was used for monitoring (mainly FastBus). The time-encoding electronics and the DAQ system have been designed to handle events at a mean rate of 2 MHz per detector with low deadtime and to minimize helicity-correlated systematic errors. In this paper, we outline the general architecture and the main features of the electronics and the DAQ system dedicated to G$^0$ forward-angle measurements.Comment: 35 pages. 17 figures. This article is to be submitted to NIM section A. It has been written with Latex using \documentclass{elsart}. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment In Press (2007