Bulletin of the American Physical Society
2006 APS April Meeting
Saturday–Tuesday, April 22–25, 2006; Dallas, TX
Session E8: Minisymposium: the Spin Structure of the Nucleon |
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Sponsoring Units: DNP Chair: Ernst Sichtermann, Lawrence Berkeley National Laboratory Room: Hyatt Regency Dallas Cumberland A |
Saturday, April 22, 2006 3:30PM - 4:06PM |
E8.00001: The Spin Structure of the Nucleon -- Present Knowledge and Open Questions Invited Speaker: The talk gives an introduction to the spin structure of the nucleon. It describes our present knowledge and addresses the most compelling open questions and their theoretical background. It also gives an overview of the current activities in the field in both theory and experiment. [Preview Abstract] |
Saturday, April 22, 2006 4:06PM - 4:18PM |
E8.00002: Double Longitudal Spin Asymmetry Measurement and Cross-section for Inclusive Jets at $\sqrt{s}$=200 GeV in polarized p+p collisions Julie Millane One of the STAR Spin Collabroation's goals is to determine the proton's polarized gluon distribution for 0.01$<$x$_g<$0.3. The STAR Collaboration takes data at RHIC, which collides polarized protons. A time projection chamber and electromagnetic calorimeter allow pseudorapidity coverage from -1 to +2. A progress report on the 2005 double spin asymmetry measurement will be the focus of this contribution. This measurement has approximately 3 pb$^{-1}$ of data at $\sqrt{s}$=200GeV. Jet transverse momentum coverage is 5$<$pt$<$20 GeV. In 2005 there was increased luminosity, improved jet trigger rates and higher polarization over previous years. Comparisons of A$_{LL}$ to various inclusive jets A$_{LL}$ predictions based on several gluon polarization scenarios will be made. 2003/2004 cross-section and double spin asymmetry measurements will also be presented. These measurements have approximately 1 pb$^{-1}$ of data. Jet transverse momentum for the cross-section measurement is 5$<$pt$<$50 GeV. The cross-section will be compared to NLO pQCD calculations and to simulations. [Preview Abstract] |
Saturday, April 22, 2006 4:18PM - 4:30PM |
E8.00003: Spin Structure in the Resonance Region Frank R. Wesselmann The RSS collaboration has measured the spin structure functions of the proton and the deuteron at Jefferson Lab using the lab's polarized electron beam, the Hall~C HMS spectrometer and the UVa polarized solid target. The asymmetries $A_{\|}$ and $A_{\perp}$ were measured at the elastic peak and in the region of the nucleon resonances ($0.70 \; \mathrm{GeV} < W < 1.98 \; \mathrm{GeV}$) at an average four momentum transfer of $Q^2 = 1.3 \; \mathrm{GeV}^2$. The extracted spin structure functions and their kinematic dependence make a significant contribution in the study of higher-twist effects and polarized duality tests. [Preview Abstract] |
Saturday, April 22, 2006 4:30PM - 4:42PM |
E8.00004: Measurement of the double spin asymmetry A$_{LL}$ from inclusive charged pion production in polarized p+p collisions at 200 GeV. A. Kocoloski A primary goal of the RHIC Spin program is the measurement of the polarized gluon distribution function $\Delta g$, which can be obtained from a global analysis incorporating measurements of the double spin asymmetry A$_{LL}$ in various final state channels of polarized p+p collisions. Final states with large production cross sections such as inclusive jet and hadron production are analyzed as the program moves towards the measurement of A$_{LL}$ in the theoretically clean channel of prompt photon production. The channels $\vec {p}+\vec {p}\to \pi ^{+/-}+X$ are unique in that the ordering of the measurements of A$_{LL}$ in these two channels is sensitive to the sign of $\Delta g$. Moreover, the STAR experiment has already established the procedure for the identification of charged pions and the calculation of their production cross-sections over a broad kinematic range. This contribution will present progress towards measurements of A$_{LL}$ extracted from inclusive charged pion yields in the transverse momentum region $2$<$p_{T}$<$12$ GeV/c. These yields were obtained from $\sim $3 pb$^{-1}$ of data taken by STAR at $\sqrt s $=200 GeV in 2005. [Preview Abstract] |
Saturday, April 22, 2006 4:42PM - 4:54PM |
E8.00005: Indirect Determination of the GDH Integrand on the Deuteron near Photodisintegration Threshold M.A. Blackston, M.A. Ahmed, B.E. Norum, B. Sawatzky, H.R. Weller Data obtained from measurements\footnote{B. Sawatzky, Ph.D. thesis, Univ. of Virginia, 2005.} recently performed at the High Intensity $\vec{\gamma}$-ray Source (HI$\vec{\gamma}$S) are being analyzed to extract the Gerasimov-Drell-Hearn (GDH) integrand on the deuteron at $\gamma$-ray energies of 3.5, 4.0, 6.0, and 10.0 MeV. Linearly polarized $\gamma$-rays were used to extract the shape of the polarized differential cross section for the $d(\vec{\gamma},n)p$ reaction near breakup threshold using the 88 neutron detectors of the BLOWFISH array. The coefficients of a Legendre polynomial expansion of the data were extracted and written in terms of the amplitudes and phases of the transition matrix elements. A grid search was performed to determine the amplitudes of the T-matrix elements, using the phase shifts obtained from $n$-$p$ scattering data\footnote{SAID Analysis, http://gwdac.phys.gwu.edu/.} to fix the relative phases. The amplitudes are used in a low-energy expansion of the GDH integrand to determine the integrand values at each energy. This talk will provide a brief overview of the experiment, describe how the amplitudes were extracted, and compare the results obtained for the GDH integrand to theory\footnote{H. Arenh\"ovel {\it et al.} Nucl. Phys., {\bf A631}(1998) 612c.}. [Preview Abstract] |
Saturday, April 22, 2006 4:54PM - 5:06PM |
E8.00006: The Generalized GDH Sum Rule: Measuring the Spin Structure of $\mathrm{^3He}$ and the Neutron using Nearly Real Photons Jaideep Singh The Gerasimov-Drell-Hearn (GDH) sum rule is one of the most important tools available to study nucleon spin structure. Originally derived for real photon absorption ($Q^2=0$), the GDH sum rule has been generalized to finite $Q^2$. The goals of Jefferson Lab experiment E97-110 are to measure the $Q^2$ dependence of the GDH integral between 0.02 and 0.3 $(\mathrm{GeV}/c)^2$, to study the slope of the GDH integral at $Q^2 \approx 0$, and to extrapolate to the real photon point for $\mathrm{^3He}$ and the neutron. In this domain, the measurement of the generalized GDH integral tests Chiral Perturbation Theory and probes its limits of applicability at low $Q^2$. The low $Q^2$ measurements from this experiment will provide new constraints on understanding the $\mathrm{^3He}$ and neutron spin structure and a better understanding of the effect of nucleon resonances. Data collection was completed in August 2003 using the Jefferson Lab high polarization continuous electron beam and a polarized $\mathrm{^3He}$ target. The status of the data analysis and future perpectives will be discussed. [Preview Abstract] |
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