R. Alarcon

-Measurement of the proton's electric to magnetic form factor ratio from 1H(over -->)(e(over -->),e'p).

We report the first precision measurement of the proton electric to magnetic form factor ratio from spin-dependent elastic scattering of longitudinally polarized electrons from a polarized hydrogen internal gas target. The measurement was performed at the MIT-Bates South Hall Ring over a range of four-momentum transfer squared Q2 from 0.15 to 0.65 (GeV/c)(2). Significantly improved results on the proton electric and magnetic form factors are obtained in combination with existing cross-section data on elastic electron-proton scattering in the same Q2 region.

Measurement of the proton's electric to magnetic form factor ratio from H→1(e→,e′p)

We report the first precision measurement of the proton electric to magnetic form factor ratio from spin-dependent elastic scattering of longitudinally polarized electrons from a polarized hydrogen internal gas target. The measurement was performed at the MIT-Bates South Hall Ring over a range of four-momentum transfer squared Q2 from 0.15 to 0.65 (GeV/c)(2). Significantly improved results on the proton electric and magnetic form factors are obtained in combination with existing cross-section data on elastic electron-proton scattering in the same Q2 region.

Measurement of T20 in Elastic Electron-Deuteron Scattering

The authors report on a measurement of the tensor analyzing power T{sub 20} in elastic electron-deuteron scattering in the range of four-momentum transfer from 1.8 to 3.2 fm{sup {minus}1}. Electrons of 704 MeV were scattered from a polarized deuterium internal target. The tensor polarization of the deuterium nuclei was determined with an ion-extraction system, allowing an absolute measurement of T{sub 20}. The data are described well by a non-relativistic calculation that includes the effects of meson-exchange currents.

The Charge Form Factor of the Neutron at Low Momentum Transfer from the H-2-polarized (e-polarized, e-prime n) p Reaction

We report new measurements of the neutron charge form factor at low momentum transfer using quasielastic electrodisintegration of the deuteron. Longitudinally polarized electrons at an energy of 850 MeV were scattered from an isotopically pure, highly polarized deuterium gas target. The scattered electrons and coincident neutrons were measured by the Bates Large Acceptance Spectrometer Toroid (BLAST) detector. The neutron form factor ratio GEn/GMn was extracted from the beam-target vector asymmetry AedV at four-momentum transfers Q2=0.14, 0.20, 0.29, and 0.42 (GeV/c)2.

Nab: Measurement principles, apparatus and uncertainties

The Nab collaboration will perform a precise measurement of a, the electron-neutrino correlation parameter, and b, the Fierz interference term in neutron beta decay, in the Fundamental Neutron Physics Beamline at the SNS, using a novel electric/magnetic field spectrometer and detector design. The experiment is aiming at the 10{sup -3} accuracy level in {Delta}a/a, and will provide an independent measurement of {lambda} = G{sub A}/G{sub V}, the ratio of axial-vector to vector coupling constants of the nucleon. Nab also plans to perform the first ever measurement of b in neutron decay, which will provide an independent limit on the tensor weak coupling.

The Charge Form Factor of the Neutron at Low Momentum Transfer from the

We report new measurements of the neutron charge form factor at low momentum transfer using quasielastic electrodisintegration of the deuteron. Longitudinally polarized electrons at an energy of 850 MeV were scattered from an isotopically pure, highly polarized deuterium gas target. The scattered electrons and coincident neutrons were measured by the Bates Large Acceptance Spectrometer Toroid (BLAST) detector. The neutron form factor ratio GEn/GMn was extracted from the beam-target vector asymmetry AedV at four-momentum transfers Q2=0.14, 0.20, 0.29, and 0.42 (GeV/c)2.

^{2}\vec{\rm H}(\vec{\rm e},{\rm e}'{\rm n}){\rm p}

OLYMPUS is an experiment mounted by an international collaboration at DESY, Hamburg, Germany to provide a ±1% measurement of the cross section ratio of positron-proton to electron-proton elastic scattering in the range 0.6 < Q2 < 2.2 (GeV/c)2. The goal is to provide a definitive experimental verification of the generally accepted explanation of the discrepancy between cross-section and recoil polarization techniques in determination of the form factor ratio GEp(Q2)/GMp(Q2).

Reaction

Abstract A polarized deuterium target internal to a medium-energy electron storage ring is described in the context of spin-dependent (e,e′d) and (e,e′p) experiments. Tensor polarized deuterium was produced in an atomic beam source and injected into a storage cell target. A Breit-Rabi polarimeter was used to monitor the injected atomic beam polarization. An electrostatic ion-extraction system and a Wien filter were utilized to measure on-line the atomic fraction of the target gas (71 ± 2%) in the storage cell. A target thickness t ⋍ 2 × 10 13 2 H/cm 2 was achieved. The target tensor polarization was varied from P zz + = 0.49(3) to P zz − = −0.89(6) while keeping the vector polarization P z at zero. The luminosity was ∼ 2 × 10 31 e − · 2 H · cm −2 s −1 at a beam current of 120 mA. The performance was stable over a fiv running period. A large acceptance non-magnetic detector system was used for the electron-proton (deuteron) coincidence measurement. It is demonstrated that these techniques result in low backgrounds due to scattering from species other than the polarized target gas and allow for fast and flexible orientation of the target spin. Specific issues such as interfacing the experiment to the storage ring and monitoring the performance of the target system are discussed in detail.

The OLYMPUS experiment

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.

Performance of a Polarized Deuterium Internal Target in a Medium-Energy Electron Storage Ring.

Abstract We present the ion-optical and physical design of a magnetic spectrometer specifically tailored for out-of-plane coincidence (e, e′p) measurements. Four such spectrometers, together with a support system which permits them to be arrayed azimuthally about a symmetry axis in the scattering plane, comprise an out-of-plane spectrometer (OOPS) cluster. The instrument is optimized for high precision measurements on the nucleon and on few body nuclear systems.