D. Barkhuff

The Strange Quark Contribution to the Proton's Magnetic Moment

Abstract We report a new determination of the strange quark contribution to the protons magnetic form factor at a four-momentum transfer Q 2 =0.1 (GeV/ c ) 2 from parity-violating e – p elastic scattering. The result uses a revised analysis of data from the SAMPLE experiment which was carried out at the MIT-Bates Laboratory. The data are combined with a calculation of the protons axial form factor G e A to determine the strange form factor G s M ( Q 2 =0.1)=0.37±0.20±0.26±0.07. The extrapolation of G s M to its Q 2 =0 limit and comparison with calculations is also discussed.

Parity violation in elastic electron-proton scattering and the proton's strange magnetic form factor

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.

Parity-Violating Electron Deuteron Scattering and the Proton's Neutral Weak Axial Vector Form Factor

We report on a new measurement of the parity-violating asymmetry in quasielastic electron scattering from the deuteron at backward angles at Q2=0.038 (GeV/c)2. This quantity provides a determination of the neutral weak axial vector form factor of the nucleon, which can potentially receive large electroweak corrections. The measured asymmetry A=-3.51+/-0.57 (stat)+/-0.58 (syst) ppm is consistent with theoretical predictions. We also report on updated results of the previous experiment at Q2=0.091 (GeV/c)2, which are also consistent with theoretical predictions.

Measurement of the vector analyzing power in elastic electron-proton scattering as a probe of the double virtual Compton amplitude.

We report the first measurement of the vector analyzing power in inclusive transversely polarized elastic electron-proton scattering at Q^2=0.1(GeV/c)^2 and large scattering angles. This quantity must vanish in the single virtual photon exchange, plane-wave impulse approximation for this reaction, and can therefore provide information on two photon exchange amplitudes for electromagnetic interactions with hadronic systems. The observable we have measured is driven by the imaginary part of the two photon exchange amplitude, the hadronic side of which is simply the Compton amplitude for the proton with two virtual photons. We find a small but nonzero value of A=-15.4±5.4 ppm.

Induced Proton Polarization for pi0 Electroproduction at Q2 = 0.126 GeV2/c2 Around the Delta(1232) Resonance

We present a measurement of the induced proton polarization P{sub n} in {pi}{sup 0} electroproduction on the proton around the {Delta} resonance. The measurement was made at a central invariant mass and a squared four-momentum transfer of W = 1231 MeV and Q{sup 2} = 0.126 GeV{sup 2}/c{sup 2}, respectively. We measured a large induced polarization, P{sub n} = -0.397 {+-} 0.055 {+-} 0.009. The data suggest that the scalar background is larger than expected from a recent effective Hamiltonian model.

Measurement of the transverse–longitudinal cross sections in the p(e→,e′p)π0 reaction in the Δ region

Accurate measurements of the p(e,e?p)pi0 reaction were performed at Q^2=0.127(GeV/c)^2 in the Delta resonance energy region. The experiments at the MIT-Bates Linear Accelerator used an 820 MeV polarized electron beam with the out of plane magnetic spectrometer system (OOPS). In this paper we report the first simultaneous determination of both the TL and TL? (``fifth or polarized) cross sections at low Q^{2} where the pion cloud contribution dominates the quadrupole amplitudes (E2 and C2). The real and imaginary parts of the transverse-longitudinal cross section provide both a sensitive determination of the Coulomb quadrupole amplitude and a test of reaction calculations. Comparisons with model calculations are presented. The empirical MAID calculation gives the best overall agreement with this accurate data. The parameters of this model for the values of the resonant multipoles are |M_{1+}(I=3/2)|= (40.9 pm 0.3)10^{-3}/m_pi, CMR= C2/M1= -6.5 pm 0.3%, EMR=E2/M1=-2.2 pm 0.9%, where the errors are due to the experimental uncertainties.

Measurement of the [Formula Presented] response function for [Formula Presented] electroproduction at [Formula Presented] in the [Formula Presented] transition

Quadrupole amplitudes in the

An energy feedback system for the MIT/Bates linear accelerator

gamma^{*}NtoDelta

Electron scattering with polarized beams at MIT-Bates accelerator center

transition are associated with the issue of nucleon deformation. A search for these small amplitudes has been the focus of a series of measurements undertaken at Bates/MIT by the OOPS collaboration. We report on results from H

Strange Magnetism and the Anapole Structure of the Proton

(e,e^prime p)pi^0