Bulletin of the American Physical Society
81st Annual Meeting of the APS Southeastern Section
Volume 59, Number 18
Wednesday–Saturday, November 12–15, 2014; Columbia, South Carolina
Session GB: Nuclear/Hadronic Physics I |
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Chair: Simonetta Liuti, University of Virginia Room: Lexington |
Friday, November 14, 2014 8:30AM - 9:06AM |
GB.00001: TBD Invited Speaker: Alexandre Deur |
Friday, November 14, 2014 9:06AM - 9:42AM |
GB.00002: TBD Invited Speaker: Nadia Fomin |
Friday, November 14, 2014 9:42AM - 9:54AM |
GB.00003: Parity-Violating and Parity-Conserving Asymmetries in \boldmath$\vec{e}p$ and \boldmath$\vec{e}N$ Scattering in the Qweak Experiment Wouter Deconinck The Qweak experiment at Jefferson Lab has made the first determination of the weak charge of the proton in elastic scattering of longitudinally polarized electrons from unpolarized protons at a momentum transfer $Q^2$ of 0.025 (GeV/c)$^2$. To achieve the required precision to measure the small parity-violating asymmetry of -279 parts per billion, we directed a 180 $\mu$A 85\%-polarized electron beam on a 35 cm long liquid hydrogen target and integrated scattered events in eight azimuthally symmetric fused silica Cerenkov detectors. Based on 4\% of the total data collected by the experiment, we find a value for the weak charge of proton in agreement with predictions of the Standard Model. To correct for the contributions from background processes, we conducted several additional parity-violating and parity-conserving asymmetry measurements with different kinematics (elastic and $N \to \Delta$), electron polarization (longitudinal and transverse), and targets (protons, electrons, aluminum, and carbon). In many cases, these ancillary results are first or high-precision measurements as well. I will discuss the analysis and results of the main experiment with a focus on several of the ancillary results. [Preview Abstract] |
(Author Not Attending)
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GB.00004: The GlueX Start Counter Eric Pooser The GlueX experiment will study meson photoproduction with unprecedented precision. This experiment will use the coherent bremsstrahlung technique to produce a 9 GeV linearly polarized photon beam incident on a liquid $\mathrm{H_{2}}$ target. A Start Counter detector has been fabricated to identify the accelerator electron beam buckets, approximately 2 ns apart, and to provide accurate timing information which is used in the level--1 trigger of the experiment. This detector is designed to operate at photon intensities of up to $\mathrm{10^{8}\gamma/s}$ in the coherent peak and provide a timing resolution $\mathrm{<\ 350\ ps}$ so as to provide successful identification of the electron beam buckets to within 99$\%$ accuracy. Furthermore, the Start Counter detector will provide excellent solid angle coverage, $\sim 90 \%\ \mathrm{of}\ 4 \pi\ \mathrm{hermeticity}$, and a high degree of segmentation for background rejection. It consists of a cylindrical array of 30 scintillators with pointed ends that bend towards the beam at the downstream end. Silicon PhotoMultiplier (SiPM) detectors have been selected as the readout system. The physical properties of the Start Counter have been studied extensively. The results of theses studies are discussed. [Preview Abstract] |
Friday, November 14, 2014 10:06AM - 10:18AM |
GB.00005: Preliminary Results of Polarization Observables $T$ and $F$ in the $\vec p(\vec \gamma,\pi^0)p$ Reaction Hao Jiang The theory which describes the interaction of quarks is Quantum Chromodynamics (QCD), but how quarks are bound inside a nucleon is not yet well understood. Pion photoproduction experiments reveals important information about the nucleon excited states and the dynamics of the quarks within it and thus provides a useful tool in the study of QCD. Detailed information about this reaction can be obtained in experiments which utilize polarized photon beams and polarized targets. Pion photoproduction in the $\gamma p \to \pi^0 p$ reaction has been measured in the FROST experiment at the Thomas Jefferson National Accelerator Facility. In this experiment circularly polarized photons with energies up to 3~GeV impinged on a transversally polarized frozen-spin target. Final-state protons were detected in the CEBAF Large Acceptance Spectrometer. Preliminary results of the polarization observables $T$ and $F$ have been extracted. The data generally agree with present partial-wave analyses, but also show marked differences. The data will constrain further partial-wave analyses and improve the extraction of proton resonance properties. This work is supported in parts by the U.S. National Science Foundation: NSF PHY-1205782. [Preview Abstract] |
Friday, November 14, 2014 10:18AM - 10:30AM |
GB.00006: Exclusive $\pi^{-}$ Electroproduction off the Neutron in Deuterium in the Resonance Region Ye Tian The goal of our research is to extract the exclusive ${\gamma}^{\ast}(n) \rightarrow p^{+} {\pi}^{-}$ reaction cross section from the deuterium data and to determine the final-state-interaction (FSI) correction factor (R). The ``e1e'' CLAS data taken in Hall B at Thomas Jefferson National Accelerator Laboratory, that we analyze, includes both a hydrogen and deuterium target run period, which allows a combined analysis of pion electroproduction off the free proton, the bound proton, and the bound neutron. Hence it will provide the experimentally best possible information about the off-shell and final state interaction effects in deuterium, which must be considered in order to extract the neutron cross section. The good agreement of the inclusive cross section off deuterium with the world data not only verified that the electron identification and fiducial cuts are proper, but also confirms that the normalization used in the exclusive channel is right. In this talk, I will present the current data analysis status, the FSI correction factor calculation, and potentially preliminary cross-section results. [Preview Abstract] |
Friday, November 14, 2014 10:30AM - 10:42AM |
GB.00007: Total Photon Absorption Cross Section Measurements for $^{12}$C and $^{28}$Si Nuclear Targets Ursula Salamonowicz Absorption of high-energy photons in nuclear matter takes place predominately through the following fundamental processes: photoelectric effect, Compton scattering, and e$+$e- pair production. At the GeV energy range, pair production is the dominating process. The total absorption cross sections for photons interacting with $^{12}$C and $^{28}$Si nuclear targets have been measured in the energy range of 4.4 GeV to 5.2 GeV with high statistics. These measurements were performed during the PrimEx-II experiment in Hall B at Jefferson Laboratory. Hall B high-resolution photon tagging facility was used together with the PrimEx Pair Spectrometer magnet and Total Absorption Counter. Preliminary results for these measurements will be presented in this talk and compared with previous experimental results. [Preview Abstract] |
Friday, November 14, 2014 10:42AM - 10:54AM |
GB.00008: Identification of possible proton two-quasiparticle band in $^{158}$Sm J.H. Hamilton, E.H. Wang, A.V. Ramayya, J.K. Hwang, S.H. Liu, N.T. Brewer, Y.X. Luo, J.O. Rasmussen, S.J. Zhu, G.M. Ter-Akopian, Yu. Ts. Oganessian High-spin states in neutron-rich $^{158}$Sm have been re-investigated by measuring the prompt $\gamma$-rays emitted in the spontaneous fission of $^{252}$Cf. A new negative-parity band has been established up to spin 12. By comparing with the theoretical calculations [1], a two-quasiparticle proton state with $\pi$5/2[532]$\otimes$$\pi$5/2[413] configuration has been proposed for the band head. The level energies are similar to those of the known levels in the negative two-quasiparticle neutron band [2,3] as predicted by theoretical calculations [1]. The systematics of the two-quasiparticle states and bands in this region are discussed.\\[4pt] [1] Y-C Yang et al., J. Phys. {\bf G37}, 085110 (2010).\\[0pt] [2] S.J. Zhu et al., J. Phys. {\bf G21}, L57 (1995).\\[0pt] [3] G.S. Simpson et al., Phys. Rev. {\bf C80}, 024304 (2009). [Preview Abstract] |
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