Search

In order to test modern theories of two-nucleon bound and scattering states, we have measured the spin polarization of ejectile protons in the electrodisintegration reaction d( e → ,e′ p → )n . Compared with spin-averaged observations, these observables offer the potential of enhanced sensitivity to details of the reaction process. The experiment was carried out in quasielastic kinematics ( q μ q μ =−2m p ω=−0.38 GeV2/c2). Protons were detected at two angles corresponding to neutron recoil momenta pr of 0 and 100 MeV/c. Full nonrelativistic calculations of the polarization transfer components sl and st, including leading order relativistic contributions, describe our measurements well, but calculations of the induced polarization sn at pr=100 MeV/c underpredict the experimental result.

We report a measurement of the neutron detection efficiency for an array of neutron detectors behind a lead-steel wall consisting of 10.16 cm thick lead bricks sandwiched between 3.18 cm steel plates. The neutron detection efficiency e was obtained from the ratio of coincidence to single-arm proton cross sections using the γ + 2 1 H → p + n reaction. Knowledge of the neutron detection efficiency was necessary to extract the cross section for the exclusive 2 H(e,′e n) 1 H reaction, which we used to obtain the elastic magnetic form factor G M n of the neutron. The measurements for three different neutron energies were carried out at the MIT-Bates Linear Accelerator Center with an incident electron beam energy of 254 MeV.

We have built and tested a system that can rapidly reject focal plane polarimeter events whose scattering angle is less than some predetermined minimum value. This produces both a greater system live time and a significant enhancement in the proportion of useful events in the recorded data. The test is based on a pattern recognition scheme employing the LeCroy memory lookup unit. A system decision time of 180 ns has been achieved.

We report a new measurement of the parity-violating asymmetry in elastic electron scattering from the proton at backward scattering angles. This asymmetry is sensitive to the strange magnetic form factor of the proton as well as electroweak axial radiative corrections. The new measurement of A=-4.92 +- 0.61 +- 0.73 ppm provides a significant constraint on these quantities. The implications for the strange magnetic form factor are discussed in the context of theoretical estimates for the axial corrections., 4 pages, 3 figures, submitted to Physical Review Letters, Sept 1999