Bulletin of the American Physical Society
2008 Annual Meeting of the Division of Nuclear Physics
Volume 53, Number 12
Thursday–Sunday, October 23–26, 2008; Oakland, California
Session GB: Electromagnetic Interactions I |
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Chair: Dennis Skopik, Thomas Jefferson National Accelerator Facility Room: Room 208 |
Saturday, October 25, 2008 10:30AM - 10:42AM |
GB.00001: Measuring the Anti-quark Flavor Asymmetry in the Nucleon Rusty Towell Fermilab E866/NuSea performed the first measurements of Drell-Yan cross section ratio of p+p to p+d collisions over a large kinematic range, allowing the extraction of the ratio of anti-down to anti-up quarks in the proton. After reviewing E866 results, improvements that can be made on these measurements by taking advantage of the Fermilab Main Injector will be discussed. The lower energy of the Main Injector provides a higher Drell-Yan cross section, allowing the extension of all measurements to higher Bjorken-x with a modified spectrometer. E906 is an approved experiment that expects to make these measurements in the near future. Our goals, spectrometer design, and schedule will be presented. [Preview Abstract] |
Saturday, October 25, 2008 10:42AM - 10:54AM |
GB.00002: Exclusive $\pi^{-}$ Electro-production from the Neutron in the Resonance Region Jixie Zhang The study of baryon resonances is crucial to our understanding of nucleon structure and dynamics. Although the excited states of the proton have been studied in great detail, there are very few data available for the neutron resonances because of the difficulty inherent in obtaining a free neutron target. To overcome this limitation, the spectator tagging technique was used in one of the CEBAF Large Acceptance Spectrometer(CLAS) collaboration experiments, \textit{Barely off-shell Nuclear Structure (BoNuS)}, in Hall-B at Jefferson Lab. We have constructed a radial time projection chamber (RTPC) based on the gaseous electron multiplier (GEM) technology to detect recoil protons with momenta from 70 to 200 MeV/c. Electron scattering data were taken in 2005 with beam energies of 2.1, 4.2 and 5.3 GeV using a 7 atm gaseous deuterium target in conjunction with the RTPC and CLAS detectors. We have analyzed exclusive $D(e, e' \pi^{-} p) p$ events in which the proton was detected either in CLAS or in the RTPC. Preliminary cross sections will be presented for this reaction. [Preview Abstract] |
Saturday, October 25, 2008 10:54AM - 11:06AM |
GB.00003: Hard Photo-disintegration of proton pairs in $^3$He Ishay Pomerantz, Eli Piasetzky, Ronald Gilman Hard deuteron photo-disintegration has been investigated for 20 years, as its cross sections follow the constituent counting rules and it provides insight into the interplay between hadronic and quark-gluon degrees of freedom in high-momentum transfer exclusive reactions. During the summer of 2007, at Jefferson lab, Hall A, we measured for the first time hard $pp$-pair disintegration in the reaction $\gamma \, ^3 {\rm He} \to pp + n$, using kinematics corresponding to a spectator neutron. The current state of the analysis and preliminary results will be shown. Clues to the underlying physics can be found in the comparison of our measurements with deuteron photo-disintegration, the energy dependence of the cross sections at 90$^{\circ}$ c.m., and the $\alpha_n$ distribution. [Preview Abstract] |
Saturday, October 25, 2008 11:06AM - 11:18AM |
GB.00004: Probing Cold Dense Nuclear Matter Douglas Higinbotham The nucleons in the nucleus can form strongly correlated pairs. Recent scattering experiments, in which a proton is knocked-out from carbon with high-momentum transfer and high missing momentum, have shown that neutron-proton pairs are nearly 20 times as prevalent as proton-proton and, by inference, neutron-neutron pairs. This result, which is due to tensor correlations, has implications for our understanding of nuclear systems from nuclei to neutron stars. [Preview Abstract] |
Saturday, October 25, 2008 11:18AM - 11:30AM |
GB.00005: A measurement of the nuclear dependence of hadronization of neutral kaons Aji Daniel Understanding the confinement of quarks and gluons in hadrons is one of the great challenges in hadronic physics. Semi-inclusive measurements of deep inelastic electron scattering from nuclei provide a unique testing ground to study the process of hadron formation. The space-time features and the nuclear dependence of quark propagation and hadronization can be extracted by comparing the production of various hadronic species from a number of target nuclei under different kinematic conditions. I will present preliminary results on the multiplicity ratios of $K^{0}_{s}$ as a function of $z(=\frac{E_{h}}{\nu})$ and $P_{T}^{2}$ from Jefferson Lab experiment E02-104. The CLAS large acceptance detector, with an electron beam of energy 5 GeV, was used to study the nuclear dependence of neutral kaon production. Data on multiplicity ratios of hadrons with strangeness will provide further input for theories of hadronization, inspired by dynamical models of QCD. [Preview Abstract] |
Saturday, October 25, 2008 11:30AM - 11:42AM |
GB.00006: Impulse Approximation limitations to the $(e,e'p)$ reaction on $^{208}$Pb and $^{12}$C: extracting spectroscopic factors as a function of Q$^2$ Joaquin Lopez Herraiz, Juan Carlos Cornejo Experiment E06007 at Jefferson Lab measured cross sections for the $(e,e'p)$ reaction at constant $(\textbf{q},\omega )$ for Q$^2$ = 0.81 GeV$^2$ over a wide range of missing momenta. At missing momentum p$_m$ = 0 MeV/c cross sections were also measured at Q$^2$ = 1.4 GeV$^2$ and 1.97 GeV$^2$ in order to investigate a possible dependence of the spectroscopic factor on Q$^2$ suggested by previous measurements. Comparison of the experimental results to theoretical predictions will be presented. [Preview Abstract] |
Saturday, October 25, 2008 11:42AM - 11:54AM |
GB.00007: Impulse Approximation limitations to the $(e,e'p)$ reaction on $^{208}$Pb: identifying relativistic effects in the nuclear medium via A$_{TL}$ measurements Alexandre Camsonne, Juan Carlos Cornejo, Joaquin Lopez Herraiz Experiment E06007 at Jefferson Lab measured cross sections for the $(e,e'p)$ reaction at constant $(\textbf{q},\omega)$ for Q$^2$ = 0.81 GeV$^2$ over a range of missing momenta from 0 to $\pm$ 500 MeV/c. A controversial issue over the last decades has been the role of relativity in the description of nuclei. A distinctive signature of dynamical relativistic effects in the nucleon wave function is the asymmetry, A$_{TL}$ in the cross section measured forward or backward of the three momentum transfer \textbf{q}. Results for the integrated cross sections for producing the low lying states of $^{207}$Tl for both positive and negative missing momenta will be presented and compared to relativistic and nonrelativistic theoretical predictions. [Preview Abstract] |
Saturday, October 25, 2008 11:54AM - 12:06PM |
GB.00008: Impulse Approximation limitations to the $(e,e'p)$ reaction on $^{208}$Pb: identifying correlations in the nuclear medium Juan Carlos Cornejo, Joaquin Lopez Herraiz Experiment E06007 at Jefferson Lab measured cross sections for the $(e,e'p)$ reaction at constant $(\textbf{q},\omega)$ for Q$^2$ = 0.81 GeV$^2$ over a range of missing momenta from 0 to 500 MeV/c. Spectroscopic factors for states near the Fermi level are typically in the range of 0.65-0.70, a feature usually attributable to correlations. A consistent description of nuclear structure requires that these correlations should also have a significant effect on the strength of high momentum components of single nucleon states. Cross sections for missing momenta from 300 MeV/c to 500 MeV/c for the $^{208}$Pb(e,e'p) reaction going to the low lying states of $^{207}$Tl will be presented and compared to theoretical predictions using various prescriptions for including correlations. [Preview Abstract] |
Saturday, October 25, 2008 12:06PM - 12:18PM |
GB.00009: Resluts of PrimEx Experiment Pawel Ambrozewicz A precision measurement of neutral pion lifetime was carried out at the Jefferson Lab - the PrimEx experiment. The measurement probed one of the most fundamental symmetry predictions of low energy Quantum Chromodynamics, the chiral anomaly, via the Primakoff effect, coherent $\pi^0$ production off a nuclear Coulomb field. The calculation of the $\pi^0$ radiative width, obtained using the transition amplitude in the chiral limit, yields 7.725 eV. Next-to-leading order calculation of this quantity, in the framework of Chiral Perturbation Theory, gives 8.1 eV $\pm$ 1.0\% while the calculation in the QCD Sum Rule regime results in 7.93 eV $\pm$ 1.5\%. Data were collected, for $^{12}C$ and $^{208}Pb$ targets, and covered a range of photon energies and angles that allowed clean separation of the Primakoff contribution from competing photoproduction processes. The validity of the measurement is confirmed by concurrent cross section measurements for two other electromagnetic processes, $e^+e^-$-pair production and Compton scattering. The result approaches the precision mentioned in recent theoretical calculations. Thus the measurement of the $\pi^0$ radiative decay width, or in turn $\pi^0$ lifetime, provides a stringent test of this theory prediction. Results will be presented. [Preview Abstract] |
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