S. F. Pate

Total cross section for p+p→p+p+π0 close to threshold

Abstract Making use of an electron-cooled beam in the IUCF storage ring, we have measured the total cross section σ tot for pp→pp π 0 at 31 bombarding energies between 285 and 325 MeV. At a level of about 5%, the data show no fluctuations that could be associated with the onset of other pion production channels. A calculation of the single-partial-wave cross section σ ss , including direct production only (no rescattering), falls short of the experiment by a factor of 5.2±0.3, but reproduces the observed energy dependence when scaled. This energy dependence is explained by contributions from the phase-space factor and the final-state interaction between the outgoing nucleons. The relative importance of higher partial waves is deduced from the energy dependence of σ tot as well as from the angular distributions of reaction protons.

Strange Quark Contributions to Parity‐Violating Asymmetries in the Backward Angle G0 Electron Scattering Experiment

D. Androić, D. S. Armstrong, J. Arvieux, S. L. Bailey, D. H. Beck, E. J. Beise, J. Benesch, F. Benmokhtar, 7 L. Bimbot, J. Birchall, P. Bosted, H. Breuer, C. L. Capuano, Y.-C. Chao, A. Coppens, C. A. Davis, C. Ellis, G. Flores, G. Franklin, C. Furget, D. Gaskell, M. T. W. Gericke, J. Grames, G. Guillard, J. Hansknecht, T. Horn, M. Jones, P. M. King, W. Korsch, S. Kox, L. Lee, J. Liu, A. Lung, J. Mammei, J. W. Martin, R. D. McKeown, M. Mihovilovic, A. Micherdzinska, H. Mkrtchyan, M. Muether, S. A. Page, V. Papavassiliou, S. F. Pate, S. K. Phillips, P. Pillot, M. L. Pitt, M. Poelker, B. Quinn, W. D. Ramsay, J.-S. Real, J. Roche, P. Roos, J. Schaub, T. Seva, N. Simicevic, G. R. Smith, D. T. Spayde, M. Stutzman, R. Suleiman, 6 V. Tadevosyan, W. T. H. van Oers, M. Versteegen, E. Voutier, W. Vulcan, S. P. Wells, S. E. Williamson, and S. A. Wood

Measurements of Deuteron Photodisintegration up to 4.0 GeV

The first measurements of the differential cross section for the d(γ,p)n reaction up to 4.0 GeV were performed at the Continuous Electron Beam Accelerator Facility (CEBAF) at Thomas Jefferson Laboratory. We report the cross sections at the proton center-of-mass angles of 36°, 52°, 69°, and 89°. These results are in reasonable agreement with previous measurements at lower energy. The 89° and 69° data show constituent-counting-rule behavior up to 4.0 GeV photon energy. The 52° and 36° data disagree with the counting-rule behavior. The quantum chromodynamics (QCD) model of nuclear reactions involving reduced amplitudes disagrees with the present data.

Determination of the Strange Form Factors of the Nucleon from vp, vp, and Parity-Violating ep Elastic Scattering

A new method of obtaining the strange form factors of the nucleon is presented, in which forward-angle parity-violating e-->p elastic scattering data are combined with nup and nu;p elastic scattering data to extract all three strange form factors: electric, magnetic, and axial (G(s)(E), G(s)(M), and G(s)(A)). In this Letter, nup and nu;p data from the Brookhaven E734 experiment are combined with the Jefferson Laboratory HAPPEX e-->p data to obtain two distinct solutions for the strange form factors at Q(2)=0.5 GeV2. More generally, combining the neutrino elastic scattering data from E734 with the existing and upcoming e-->p data will yield the strange form factors of the nucleon for Q2 of 0.45-1.05 GeV2. Measurement of G(s)(A) is crucial to the determination of the strange quark contribution to the nucleon spin Deltas.

Terascale Physics Opportunities at a High Statistics, High Energy Neutrino Scattering Experiment: NuSOnG

This paper presents the physics case for a new high-energy, ultra-high statistics neutrino scattering experiment, NuSOnG (Neutrino Scattering on Glass). This experiment uses a Tevatron-based neutrino beam to obtain over an order of magnitude higher statistics than presently available for the purely weak processes νμ + e- → νμ + e- and νμ + e- → νe + μ-. A sample of Deep Inelastic Scattering events which is over two orders of magnitude larger than past samples will also be obtained. As a result, NuSOnG will be unique among present and planned experiments for its ability to probe neutrino couplings to Beyond the Standard Model physics. Many Beyond Standard Model theories physics predict a rich hierarchy of TeV-scale new states that can correct neutrino cross-sections, through modifications of Zνν couplings, tree-level exchanges of new particles such as Z′s, or through loop-level oblique corrections to gauge boson propagators. These corrections are generic in theories of extra dimensions, extended gauge symmetries, supersymmetry, and more. The sensitivity of NuSOnG to this new physics extends beyond 5 TeV mass scales. This paper reviews these physics opportunities.

Test of a windowless storage cell target in a proton storage ring

Abstract Stored ion beams offer the possibility to use polarized internal targets that consist of a source of polarized atoms in conjunction with a long, narrow, windowless target cell to enhance the target thickness. In this paper, we discuss the effect of such a cell on the performance of the storage ring, based on measurements carried out with the Indiana Cooler. A prototype target cell was constructed and was operated with a controlled flow of H 2 target gas in a beam of stored protons. Detection of protons scattered at angles from 4° to 15° in coincidence with the associated recoil particles was used to identify elastic scattering. The results show that the presence of a 25 cm long target cell with a rectangular opening of 6.4 mm by 7.9 mm is compatible with operation of the Cooler ring. This demonstrates the feasibility of an important component of experiments with stored, polarized beams and carrier-free polarized, internal targets.

Strange Quark Contribution to the Vector and Axial Form Factors of the Nucleon: Combined Analysis of G0, HAPPEx, and Brookhaven E734 Data

The strange quark contribution to the vector and axial form factors of the nucleon has been determined for momentum transfers in the range 0.45<Q{sup 2}<1.0 GeV{sup 2}. The results are obtained via a combined analysis of forward-scattering, parity-violating elastic e-vectorp asymmetry data from the G0 and HAPPEx experiments at Jefferson Lab and elastic {nu}p- and {nu}p-scattering data from Experiment 734 at Brookhaven National Laboratory. The parity-violating asymmetries measured in elastic e-vectorp scattering at forward angles establish a relationship between the strange vector form factors G{sub E}{sup s} and G{sub M}{sup s}, with little sensitivity to the strange axial form factor G{sub A}{sup s}. However, elastic neutrino scattering at low Q{sup 2} is dominated by the axial form factor, with some significant sensitivity to the vector form factors as well. Combination of the two data sets allows the simultaneous extraction of G{sub E}{sup s},G{sub M}{sup s}, and G{sub A}{sup s} over a significant range of Q{sup 2} for the very first time. The Q{sup 2} dependence of the strange axial form factor suggests that the strange quark contribution to the proton spin, {delta}s, is negative.

Transverse beam spin asymmetries in forward-angle elastic electron-proton scattering

We have measured the beam-normal single-spin asymmetry in elastic scattering of transversely polarized 3 GeV electrons from unpolarized protons at Q2=0.15, 0.25 (GeV/c)2. The results are inconsistent with calculations solely using the elastic nucleon intermediate state and generally agree with calculations with significant inelastic hadronic intermediate state contributions. A(n) provides a direct probe of the imaginary component of the 2gamma exchange amplitude, the complete description of which is important in the interpretation of data from precision electron-scattering experiments.

Spin-dependent scattering of polarized protons from a polarized 3He internal gas target

We describe the first experiment to use a polarized internal gas target and polarized beam in a storage ring. A laser optically pumped polarized 3He internal gas target has been used with circulating beams of 197–414 MeV polarized protons to carry out an extensive set of measurements of spin dependent scattering. A large acceptance non-magnetic detector system consisting of wire-chambers, scintillators and microstrip detectors was used to detect protons, neutrons, deuterons, and 3He nuclei from the beam-target interaction. It is demonstrated that these techniques result in low backgrounds (< 1%) due to scattering from species other than the polarized target gas and allow detection of low energy recoiling nuclei. Specific issues such as interfacing the experiment to the storage ring and monitoring the luminosity and polarizations are discussed in detail.

THE HERMES POLARIZED 3HE INTERNAL GAS TARGET

Abstract The HERMES experiment is investigating the spin structure of the proton and neutron via deep-inelastic scattering of polarized positrons from polarized nuclear targets. The polarized positrons are provided by the HERA positron storage ring at DESY, Hamburg, Germany. The targets are pure internal gas targets. Data acquisition began in 1995, utilizing a polarized 3 He internal gas target to study the spin structure of the neutron. The target gas was polarized using the metastability-exchange optical-pumping technique and then injected into a cryogenically cooled target cell. The target was designed to operate with either longitudinal or transverse directions of polarization. Operating conditions included polarizations of up to 54% and target thicknesses of 1×10 15 nucleons/cm 2 . In this paper the HERMES polarized 3 He internal gas target is described in detail.