Bulletin of the American Physical Society
APS April Meeting 2010
Volume 55, Number 1
Saturday–Tuesday, February 13–16, 2010; Washington, DC
Session P11: Electromagnetic Interactions |
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Sponsoring Units: DNP Chair: Douglas Higinbotham, Thomas Jefferson National Accelerator Facility Room: Maryland C |
Monday, February 15, 2010 10:45AM - 10:57AM |
P11.00001: Measurement of Single-spin Asymmetry in Charged Kaon Electroproduction on a Transversely Polarized $^3$He Target Youcai Wang Data on target single-spin asymmetry in the semi-inclusive deep inelastic $\vec{n}(e,e'K^{\pm})X$ reaction have been taken in Hall A at Jefferson Lab using a transversely polarized $^3$He target and an electron beam of 5.9 GeV. This measurement covers the kinematic region, $x = 0.13\sim 0.41$, at $Q^2=1.3\sim 3.1~ (\mathrm{GeV}/c)^2$. In coincidence with the scattered electrons detected in the large-acceptance BigBite spectrometer, kaons were detected in the high-resolution spectrometer and identified using an aerogel and Ring-Imaging Cherenkov (RICH) detectors together with time-of-flight (TOF) information. The kaon and pion single-spin asymmetry data from this experiment are expected to provide constraints on the flavor dependence of the transversity and the Sivers distribution functions. The performance of the aerogel, TOF, and RICH for kaon identification, as well as some preliminary results of the analysis, will be presented. [Preview Abstract] |
Monday, February 15, 2010 10:57AM - 11:09AM |
P11.00002: Target Normal Single-Spin Asymmetry in Inclusive DIS Timothy Holmstrom An experiment (E07--013) to measure the target normal single spin asymmetry $A^n_N$ in inclusive deep-inelastic $n^{\uparrow}(e,e')$ reaction with a vertically polarized $^3$He target has completed data collection during Jefferson Lab's Hall A neutron transversity experiment (E06--010) in Fall of 2008. The expected accuracy of this measurement is $\delta A^n_N = 3 \times 10^{-3}$. The target normal spin asymmetry in DIS probes helicity--flip amplitudes at the quark level that are related to effects beyond the leading-twist picture of DIS. In view of the predicted rapid variation of the asymmetry between $10^{-2}$ (exclusive) and $10^{-4}$ (DIS-inclusive), a non-zero measurement would be sensitive to the transition from hadronic to partonic degrees of freedom. The status and perspectives of the data analysis will be discussed. [Preview Abstract] |
Monday, February 15, 2010 11:09AM - 11:21AM |
P11.00003: Measuerment of generalized form factors near the pion threshold in high $Q^2$ region with CLAS Kijun Park The recent development of experimental techniques allow us to study threshold pion production in high-energy experiments and particularly, electro-production with photon virtuality $Q^2$ in a few $\rm{GeV^2}$ range. The experiments with fine energy resolution make a major step to come close to the production threshold to suppress the P-wave contribution ($M_{1+}$). The recent prediction based on the Light-Cone Sum Rule (LCSR), one can calculate the hadron form factors in terms of distribution amplitudes that approach perturbative Quantum Chromo-Dynamics (pQCD) without other non-perturbative parameters in high energy regime. The extraction of the generalized form factors near the pion threshold are estimated by the S- wave multipole dominance in the LCSR framework. We extracted the generalized form factors for the first time in the exclusive channel ( $ep \to en\pi^+$) using CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab. The kinematic ranges are from $2.05\;\rm{GeV^2}$ to $4.5\;\rm{GeV^2}$ for $Q^2$ and $1.11\;\rm{GeV}$ to $1.15\;\rm{GeV}$ for the invariant mass range in the $n\pi^+$ system.. Preliminary results will be presented and compared with the calculation from LCSR, MAID and multipole analysis. [Preview Abstract] |
Monday, February 15, 2010 11:21AM - 11:33AM |
P11.00004: Measurement of the proton electric to magnetic form factor ratio with polarized target at high momentum transfer Anusha Liyanage Experiment E07-003 (SANE, Spin Asymmetries of the Nucleon Experiment) has been carried out in Hall C at Jefferson Lab to study the proton spin structure functions with a dynamically polarized ammonia target and longitudinally polarized electron beam. Scattered electrons were detected by the Big Electron Telescope Array (BETA). By detecting elastically scattered protons in the High Momentum Spectrometer (HMS) in coincidence with the electrons in BETA, inclusive and elastic measurements were carried out in parallel. The elastic double spin asymmetry allows to extract the proton electric to magnetic form factor ratio at high momentum transfer, $Q^2$ = 5.75 (GeV/c)$^2$. The measurement will verify the falling of the proton form factor ratio with increasing momentum transfer observed in previous polarization transfer measurements, with a different measurement technique and systematic uncertainties uncorrelated to those of the recoil polarization measurements. Details and status of the analysis will be presented. [Preview Abstract] |
Monday, February 15, 2010 11:33AM - 11:45AM |
P11.00005: High Acceptance Proton Form Factor Measurements Up To 15 GeV$^2$ Bogdan Wojtsekhowski, Lubomir Pentchev An experiment aimed to measure the proton form factor ratio with the 12 GeV JLab machine using polarization transfer technique, is described. A large detector acceptance needed for such high $Q^2$ measurements is achieved by means of a single dipole detector system to detect the recoil proton that includes a polarimeter and a hadron calorimeter, and a highly granulated electromagnetic calorimeter for the electron registration. For the proton tracking, Gas Electron Multiplier technology is used that can sustain the high fluxes of particles due to direct view from the target. The impact of such high precision measurements on the theoretical description of the proton are discussed, as well. [Preview Abstract] |
Monday, February 15, 2010 11:45AM - 11:57AM |
P11.00006: Proton Elastic Form Factor Ratio Measurements at Low $Q^2$ Vincent Sulkosky A high-precision experiment was recently performed at Jefferson Lab in Hall A to measure the proton elastic form factor ratio $\mu_{\mathrm{p}} G_{\mathrm{E}}^{\mathrm{p}}/G_{\mathrm{M}}^{\mathrm{p}}$ for $Q^2$ between 0.3 and 0.7~$[\mathrm{GeV}/c]^{2}$. In this $Q^{2}$ region, previous data and various fits have indicated significant deviations from unity in the form factor ratio. The technique of recoil polarimetry was used with an 80\% polarized electron beam to achieve the proposed statistical uncertainty of $<$~1\%. In addition to studying nucleon structure, these results will impact few-body nuclear structure, deeply virtual compton scattering measurements, the determination of the proton Zemach radius and the extraction of the strange form factors from elastic parity violation experiments. The preliminary results will be presented, which are a few precent lower than previous world data and fits. [Preview Abstract] |
Monday, February 15, 2010 11:57AM - 12:09PM |
P11.00007: The OLYMPUS Luminosity Monitors Ozgur Ates The OLYMPUS experiment at DESY has been proposed to measure the ratio of positron-proton and electron-proton elastic scattering cross sections to quantify the effect of two-photon exchange, which is widely considered to be responsible for the discrepancy between measurements of the proton electric to magnetic form factor ratio with the Rosenbluth and polarization transfer methods. In order to control the systematic uncertainties to the percent level, precise monitoring of the luminosities is required and will be achieved by measuring the elastic count rates at forward angles and low momentum transfer with tracking telescopes based on GEM (Gas Electron Multiplier) technology. Simulation results for the design and performance of the OLYMPUS luminosity monitors will be presented. [Preview Abstract] |
Monday, February 15, 2010 12:09PM - 12:21PM |
P11.00008: Polarization Measurements of the Recoil Proton in $\pi^{0}$ Photoprodcution Wei Luo, Mark Jones, Lubomir Pentchev Perturbative QCD theory predicts that the polarization components above the baryon resonance region should have a smooth dependence of $E_{\gamma}$ and approaching limits established by hadron helicity conservation in absence of baryon resonance. Published data show strong variation of polarization variables above $2 \mbox{ GeV}$ which could be a sign of high-mass resonance. We present preliminary results of $\pi^{0}$ photoproduction in $p(\vec{\gamma},\vec{p})\pi^0$ reaction from the Jefferson Lab Hall C experiments E04-108, E04-019, E07-002 and Hall A experiment E99-114 which all measured the polarization observables of proton using recoil polarization method with high statistics. Our data extends the polarization measurement of $\pi^{0}$ photoproduction up to $E_{\gamma}=5.7 \mbox{ GeV}$ with high four momentum transfer. The results show good agreement in the overlap region with previous experiment in Hall A that $E_{\gamma}$ up to $4.1 \mbox{ GeV}$. We will discuss the interpretation of these observations. [Preview Abstract] |
Monday, February 15, 2010 12:21PM - 12:33PM |
P11.00009: Recent Results From the Two Photon Exchange Experiment at CLAS Megh Niroula Recent results from experiments conducted at Thomas Jefferson National Accelerator Facility have shown a discrepancy in the measurement of the ratio of the Electric ($G_E$) and magnetic ($G_M$) form factors of the proton measured by Rosenbluth Separation and Polarization Transfer Methods. The real part of the Two Photon Exchange (TPE) amplitude in lepton-proton elastic scattering is expected to explain this discrepancy. The ratio of elastic positron-proton to electron-proton cross sections is the only way to access this real part. Measurements of the cross section ratio using a mixed electron-positron beam in CLAS at Jefferson Lab were made. In this talk I will present results from the 2006 TPE test run. The result will focus on two bin in $Q^2$ and $\epsilon$ ($0.4\ge Q^2\le1.0$, $0.3\ge \epsilon \le0.5$ and $0.4\ge Q^2 \le1.0$, $0.75\ge\epsilon\le0.92$). [Preview Abstract] |
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