An Energy Feedback System for the MIT/Bates Linear Accelerator

We report the development and implementation of an energy feedback system for the MIT/Bates Linear Accelerator Center. General requirements of the system are described, as are the specific requirements, features, and components of the system unique to its implementation at the Bates Laboratory. We demonstrate that with the system in operation, energy fluctuations correlated with the 60 Hz line voltage and with drifts of thermal origin are reduced by an order of magnitude

The Strange Quark Contribution to the Proton's Magnetic Moment

We report a new determination of the strange quark contribution to the proton's magnetic form factor at a four-momentum transfer Q2 = 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 proton's axial form factor GAe to determine the strange form factor GMs(Q2=0.1)=0.37 +- 0.20 +- 0.26 +- 0.07. The extrapolation of GMs to its Q2=0 limit and comparison with calculations is also discussed.Comment: 6 pages, 1 figure, submitted to Phys. Lett.

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

Calibration of a Proton Polarimeter

This research was sponsored by the National Science Foundation Grant NSF PHY-931478

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(sys)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.Comment: 4 pages, 2 figures, submitted to Phys. Rev. Let

Measurement of the vector analyzing power in elastic electron-proton scattering as a probe of double photon exchange amplitudes

We report the first measurement of the vector analyzing power in inclusive transversely polarized elastic electron-proton scattering at Q2 = 0.1 (GeV/c)2 and large scattering angles. This quantity should vanish in the single virtual photon exchange, plane wave impulse approximation for this reaction, and can therefore provide information on double photon exchange amplitudes for electro- magnetic interactions with hadronic systems. We find a non-zero value of A=-15.4±5.4 ppm. No calculations of this observable for nuclei other than spin 0 have been carried out in these kinematics, and the calculation using the spin orbit interaction from a charged point nucleus of spin 0 cannot describe these data

Updated results from the SAMPLE experiment

The SAMPLE collaboration has recently completed its measurements of the parity violating elastic electron scattering asymmetry from hydrogen and the quasielastic asymmetry from deuterium [1,2,3,4,5]. Neutral weak form factors of the nucleon, both vector and axial, can be extracted from these data and used to determine the strange quark contribution to electromagnetic form factors. The results of the original measurements at a Q2 of 0.1 (GeV/c)2 [2,3] have recently been reanalyzed [4], incorporating improvements in simulation and new background data, and combined with a new measurement of the quasielastic deuteron asymmetry at a Q2 of 0.038 (GeV/c)2 [5]. Final results from this new analysis and data set will be presented.PACS: 13.60.-r Photon and charged-lepton interactions with hadrons – 11.30.Er Charge conjugation, parity, time reversal, and other discrete symmetries – 13.40.Gp Electromagnetic form factors – 14.20.Dh Protons and neutrons The Author, for the SAMPLE Collaboration. Present address: Department of Physics, Grinnell College, 1116 8th Avenue, Grinnell, IA 50112 US

Search for quadrupole strength in the electroexcitation of the Δ+ (1232)

High-precision 1H(e, elp)φ0 measurements at Q2 = 0.126 (GeV/c)2 are presented. It allows the determination of quadrupole amplitudes in the γ*N → △ transition, in which the reliability of electroproduction models was simultaneously tested. The derived quadrupole-to-dipole (I = 3/2) amplitude ratios, RSM = (-6.5 ± 0.2stat+sys ± 2.5mod)% and REM = (-2.1 ± 0.2stat+sys ± 2.0mod)%, are dominated by model error