Bulletin of the American Physical Society
2006 73rd Annual Meeting of the Southeastern Section of the APS
Thursday–Saturday, November 9–11, 2006; Williamsburg, Virginia
Session MB: Nuclear Physics III |
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Chair: David Armstrong, College of William & Mary Room: Williamsburg Hospitality House Huntington |
Saturday, November 11, 2006 8:30AM - 8:54AM |
MB.00001: Parity Violating electron scattering from Hydrogen and Helium-4 and Strangness in the nucleon: Results from HAPPEX-II Bryan Moffit The quark-antiquark pairs that form the sea within the nucleon are well established within quantum chromodynamics. Several recent and ongoing experiments are motivated by determining how this sea, containing contributions from all quark flavors, plays a role in affecting the nucleon's overall properties. Of particular interest is the possible strange quark contribution to the nucleon's electric and magnetic form factors. The recently completed HAPPEX asymmetry measurements take advantage of parity violation in elastic electron scattering to probe the strange quark effects. The measurement using a hydrogen target is sensitive to a linear combination of $G_E^s$ and $G_M^s$, the contribution to the electric and magnetic form factors due to strange quarks, respectively, whereas scattering from a spinless helium target cleanly isolates $G_E^s$. The combination of the two measurements therefore allows these form factors to be separately determined. Final results will be presented from the complete data set, obtained in runs in 2004 and 2005, yielding results of unprecedented precision. [Preview Abstract] |
Saturday, November 11, 2006 8:54AM - 9:06AM |
MB.00002: Extracting nucleon strange and anapole form factors from world data Roger Carlini, Ross Young, Anthony Thomas, Julie Roche The complete world set of parity violating electron scattering data up to Q$^{2} \quad \sim $ 0.3 GeV$^{2}$ is analyzed. We extract the current experimental determination of the strange electric and magnetic form factors of the proton, as well as the weak axial form factors of the proton and neutron, at Q$^{2}$ = 0.1 GeV$^{2}$. Within experimental uncertainties, we find the strange form factors are consistent with zero, as are the anapole contributions to the axial form factors. Nevertheless, the correlations between the strange and anapole contributions suggest that there is only a small probability that these form factors all vanish simultaneously. [Preview Abstract] |
Saturday, November 11, 2006 9:06AM - 9:18AM |
MB.00003: Rescattering of the $\Sigma ^{-}$(1385) and the K$^{+}$ on the proton, R.M. Davis (GWU), for the CLAS Collaboration Rebecca Davis Due to the short lifetime of excited hyperons, studies on their scattering are lacking. Since neither beams nor targets can be created, the only possibility is to use final-state interactions. We studied the reaction $\gamma $ n $\to $ K$^{+} \quad \Sigma ^{-}$(1385), detecting the K$^{+}$, $\pi ^{-}$, $\pi ^{-}$, p in the final state. These data were obtained in the g10 experiment at Jefferson Lab, which used real photons and a deuterium target in the CLAS. The $\Sigma ^{-}$(1385) and the intermediate $\Lambda $ were identified from their invariant masses. The additional 'spectator' proton was either detected or identified by missing mass. Once all particles were identified, we were able to look for high-t events with spectator proton momenta above 0.4 GeV/c. Though the statistics are limited, we plan to determine the quasifree and the rescattering cross sections. [Preview Abstract] |
Saturday, November 11, 2006 9:18AM - 9:30AM |
MB.00004: $\Lambda$ Hypernuclear Spectroscopy up to the Medium-Heavy Region Through the (e,e$'$K$^{+})$ Reaction Leon Cole The ``Spectroscopic Study of $\Lambda$ Hypernuclei up to the Medium-Heavy Mass Region Through the (e,e$'$K$^{+})$ Reaction'' (HKS Experiment) was successfully completed during the summer of 2005 at Jefferson Laboratory. It utilized a new High Resolution Kaon Spectrometer (HKS) and a ``Tilt Method'' on the electron arm. These features aim to achieve the best ever hypernuclear energy resolution and the highest possible production yield of $\Lambda$ Hypernuclei. The goal of the experiment is to investigate $\Lambda$ hypernuclear structures with precise measurements of the mass spectra from light to medium-heavy mass region. Such precise spectroscopy will provide valuable information on the single-particle behavior of $\Lambda$ hyperon in a nuclear medium and gain knowledge on the effective $\Lambda$-N interaction and nuclear structure probed by the $\Lambda$ hyperon. An overview of HKS experiment will be presented and preliminary results of the excitation spectra from various targets will be showcased. [Preview Abstract] |
Saturday, November 11, 2006 9:30AM - 9:42AM |
MB.00005: High Resolution 1P-Shell Hypernuclear Spectroscopy at JLAB, HALL A (E94-107) Armando Acha, Pete Markowitz Information about the force between nucleons and strange baryons, i.e. the $\Lambda$-N interaction, can be obtained by studying the spectroscopy of nuclei where a nucleon is replaced by a Lambda hyperon to form a bound state. Hypernuclear spectroscopy via electromagnetic induced reaction has been measured in Hall A at Jefferson Lab on 1p-shell nuclei, C$^{12}$, Be$^{9}$ and O$^{16}$ . The reaction constitutes an innovative experimental approach to study hypernuclei, providing an alternative to the hadronic induced reactions studied so far. Jefferson Lab's electron beam features and the available experimental equipment in Hall A offered a unique opportunity to perform this experiment. Among the features needed are a narrow beam energy spread ($\sigma$E/E~10E$^{-5}$), high resolution spectrometers (missing energy resolution less than 500 KeV FWHM) and good particle identification. Modifications were made to the Hall A standard apparatus: two superconducting septum magnets were added to the spectrometer systems to allow particle detection at very forward angles. The particle identification for the experiment required separating kaons from large pion and proton backgrounds, and electrons from pion backgrounds. Preliminary results with a missing energy resolution of 750 KeV FWHM show good correlation with available theoretical models. Details about results will be shown. [Preview Abstract] |
Saturday, November 11, 2006 9:42AM - 9:54AM |
MB.00006: Combined analysis of $\pi^+ \to {\rm e}^+\nu\gamma$ decay in the PIBETA data stream. Maxim Bychkov The PIBETA experiment, carried out at the Paul Scherrer Institute, Switzerland , has acquired the world's largest data set of radiative pion decay events $\pi^+\to e^+\nu\gamma$ to date. Radiative pion decay is the premier source of information regarding the charged pion structure, and it provides an independent check of the CVC hypothesis of the weak interactions. The data were collected in two separate runs. Analyses of the original data sample indicated possible discrepancies with the Standard Model of elementary particles, and prompted a dedicated run specifically optimized for the radiative pion decay study. In this talk we present the analysis of the dedicated run as well as a fresh look at the old data with an improved understanding of the systematic effects and with increased statistics. [Preview Abstract] |
Saturday, November 11, 2006 9:54AM - 10:06AM |
MB.00007: Redesign of the PIBETA Beam Detectors for a New $\pi_{2e}$ Experiment at PSI Emil Frlez PEN, a new experiment aiming to measure the $\pi^+\to e^+\nu$ ($\pi_{2e}$) decay branching ratio with a relative uncertainty of $\sim 5\cdot 10^{-4}$ has begun this year at the Paul Scherrer Institute ring accelerator. A development run with an upgraded PIBETA detector was conducted during the summer of 2006. In this contribution we discuss the design and performance of the new beam detectors: the upstream beam counter, and the active collimator, degrader and target using low-momentum 72-80 MeV/c $\pi^+$ beams. All beam detector waveforms were digitized with a 2 GHz/10 bit Acqiris digitizer. [Preview Abstract] |
Saturday, November 11, 2006 10:06AM - 10:18AM |
MB.00008: Search for Sub-Threshold J/psi Photoproduction Parikshit Junnarkar We present results from the recent Jefferson Lab experiment E03-008: ``Sub-threshold J/$\psi$ Photoproduction." A beam of 6 GeV electrons was impinged on a thick carbon target and lepton pairs were detected in two magnetic spectrometers in Hall C. The kinematics were sub-threshold to production from a free proton, so the experiment probed the short distance configuration in the nucleus, where one expects sensitivity to higher twist effects (such as three-gluon exchange), intrinsic charm contributions, and possible multi-quark resonances involving charmed quarks. An upper bound for the cross section near threshold will be presented. [Preview Abstract] |
Saturday, November 11, 2006 10:18AM - 10:30AM |
MB.00009: The NPDGamma Experiment: Hadronic Parity Violation in the Radiative Capture of Polarized Cold Neutrons on Protons Michael Gericke The NPDGamma experiment is currently taking data to measure the parity-violating correlation $A_\gamma$ between the neutron spin and photon direction in the capture of polarized cold neutrons on hydrogen, to a precision $5\times 10^{-9}$, 10\% of the expected value. This asymmetry measures the neutral weak hadronic coupling without the complicating effects of nuclear structure. The first phase of the experiment, at Los Alamos National Laboratory, will provide an upper limit at the $10^{-7}$ accuracy and phase two is proposed to run as the first experiment on the new fundamental neutron physics beam line at the Spallation Neutron Source at Oak Ridge National Laboratory. An overview of the experiment and related physics will be provided, together with a preliminary analysis of the phase 1 data. [Preview Abstract] |
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