Bulletin of the American Physical Society
2007 APS April Meeting
Volume 52, Number 3
Saturday–Tuesday, April 14–17, 2007; Jacksonville, Florida
Session J16: Electromagnetic Interactions II |
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Sponsoring Units: DNP Chair: Douglas Hasell, Massachusetts Institute of Technology Room: Hyatt Regency Jacksonville Riverfront City Terrace 12 |
Sunday, April 15, 2007 10:30AM - 10:42AM |
J16.00001: An experiment to measure the helicity correlation $A_{LL}$ in Compton scattering Melissa Commisso Real Compton scattering from the proton has the potential to resolve outstanding questions regarding the applicability of pQCD to exclusive reactions at intermediate energies, as well as providing access to unique form factors describable in terms of Generalized Parton Distributions (GPD's). We will describe an approved JLab experiment, E05-101, that will utilize Compton scattering to provide a precise, first ever measurement of the helicity correlation $A_{LL}$ at large $s$ and $-t$ (9 and 6.4 GeV/c$^2$, respectively). The motivation, experimental setup, and expected results will be presented. [Preview Abstract] |
Sunday, April 15, 2007 10:42AM - 10:54AM |
J16.00002: Generalized Polarizabilities of the Proton at low $Q^2$ using Virtual Compton Scattering Bourgeois Paul The Generalized Polarizabilities (GP's) of the proton are new observables that are accessible through the virtual Compton scattering (VCS) reaction. Precise measurements of the GP's will set constraints on models of the proton and will enhance our understanding of nucleon structure. My talk will focus on the use of VCS to measure the GP's, and I will present recently published results of the electric and magnetic GP's at $Q^2 \approx 0.06 \,GeV^2/c^2$. I will also present the first determination of the electric and magnetic mean square polarizability radii of the proton. [Preview Abstract] |
Sunday, April 15, 2007 10:54AM - 11:06AM |
J16.00003: Precision Measurements of Low Energy Deuteron Photodisintegration Using Linearly Polarized Beams M.A. Blackston, M.A. Ahmed, B. Bewer, R. Igarashi, B. Norum, Y. Parpottas, R. Pywell, B.A. Perdue, B.D. Sawatzky, H.R. Weller Data from a deuteron photodisintegration experiment performed at the High Intensity $\vec{\gamma}$-ray Source (HI$\vec{\gamma}$S) are being analyzed to extract the amplitudes of the Transition Matrix Elements (TMEs) that contribute to the reaction at 14 and 16 MeV. The results are compared to potential model and effective field theory (EFT) calculations. Linearly polarized $\gamma$-rays were used to extract the shape of the polarized differential cross section for the $d(\vec{\gamma},n)p$ reaction using the 88 neutron detectors of the Blowfish array. The coefficients of a Legendre polynomial expansion of the data were written in terms of the amplitudes and phases of the TMEs. The data were fit to determine the amplitudes of the TMEs, using the phase shifts obtained from $n$-$p$ scattering data to fix the relative phases. This talk will provide a brief overview of the experiment, describe how the amplitudes were extracted, and compare the results to theory. The relationship of these results to the GDH integrand of the deuteron will also be discussed. [Preview Abstract] |
Sunday, April 15, 2007 11:06AM - 11:18AM |
J16.00004: An Indirect Determination of the Gerasimov-Drell-Hearn (GDH) Sum Rule for the Deuteron at Low Energies M.W. Ahmed, M. Blackston, B. Perdue, W. Tornow, H. Weller The GDH sum rule relates the helicity dependent photoabsorption cross section asymmetry to the anomalous magnetic moment, $\kappa$, of the target. A direct measurement of the GDH sum rule for the deuteron requires polarized target and circularly polarized $\gamma$-rays. However, at low energies, an indirect measurement can be made using an unpolarized target and linearly polarized $\gamma$-rays. It is shown that near photodisintegration threshold a measurement of the analyzing power obtained with linearly polarized $\gamma$-rays can be used to extract the $^1S_0$ (M1) strength ($\sigma$(M1)) and the GDH integrand can be related to this quantity. An analysis of data from the High Intensity Gamma-Ray Source (HI$\gamma$S) on photodisintegration of the deuteron is presented. Analysis of data to extract the GDH integrand using other measurements of $\sigma$(M1) such as the analyzing power in the polarized neutron capture reaction, as well as unpolarized photodisintegration of the deuteron along with measurements of the outgoing neutron polarization will also be presented. A fit to the world data analyzed in this manner between E$_{\gamma}$ of 2.39 MeV and 10 MeV gives a GDH integralvalue of -669$^{+205}_{-43}$ $\mu$b. This result is the first confirmation of the large $^1S_0$ (M1) contribution predicted by H. Arenh\"ovel \textit{et al.} to dominate the GDH sum rule integrand of the deuteron near threshold. [Preview Abstract] |
Sunday, April 15, 2007 11:18AM - 11:30AM |
J16.00005: Measurement of Tensor Analyzing Powers in Elastic Electron Deuteron Scattering with BLAST Michael Kohl A precision measurement of the deuteron tensor analyzing powers $T_{20}$ and $T_{21}$ in elastic electron-deuteron scattering has been carried out at the MIT-Bates Linear Accelerator Center. Data were collected simultaneously over a momentum transfer range of 2.15 to 4.5 fm$^{-1}$ using a polarised, stored electron beam; the Bates Large Acceptance Spectrometer Toroid (BLAST) detector; and a highly polarized, internal deuterium gas target. The elastic deuteron form factors $G_C$ and $G_Q$ were extracted with improved precision using the new data; confirming the location of the first node of the charge monopole form factor. The new data provide strong constraints on nuclear models in a momentum transfer range covering the minimum of $T_{20}$ and the first node of $G_C$. [Preview Abstract] |
Sunday, April 15, 2007 11:30AM - 11:42AM |
J16.00006: Vector and Tensor Asymmetries for Quasielastic Scattering from Deuterium at BLAST Adam DeGrush A comprehensive study of spin-dependent electron scattering from deuterium has been carried out using the polarized electron beam of the MIT-Bates Linear Accelerator Center together with the BLAST (Bates Large Acceptance Spectrometer Toroid) detector and an internal vector/tensor polarized deuterium target. A spin-dependent analysis of exclusive quasielastic scattering over a $Q^2$ range between 0.1 and 0.5 (GeV/c)$^2$ has been made for target orientations both parallel and perpendicular to the momentum transfer. Asymmetry results and comparisons with theory will be presented along with measurements of the beam and target polarization product. [Preview Abstract] |
Sunday, April 15, 2007 11:42AM - 11:54AM |
J16.00007: Pion Electroproduction in the $\Delta$ Excitation Region Yuan Xiao The BLAST (Bates Large Acceptance Spectrometer Toroid) collaboration recently measured the spin dependence of pion electroproduction in the $\Delta$ excitation region. The experiment used the stored, polarized electron beam of the MIT-Bates Linear Accelerator Center and an internal target of polarized hydrogen produced by an atomic beam source. The BLAST detector was used to simultaneously measure both elastic and inelastic scattering from the proton in inclusive and exclusive reactions. By reversing both the target spin and the electron beam helicity, asymmetries were constructed from the measured rates with different spin combinations. This presentation will show results for the exclusive pion electroproduction reactions $^{1}\vec H(\vec e,e^{\prime}\pi^{+})n$ and $^{1}\vec H(\vec e,e^{\prime}p)\pi^{0}$. The asymmetries will be compared with several theoretical models. [Preview Abstract] |
Sunday, April 15, 2007 11:54AM - 12:06PM |
J16.00008: Pion Electroproduction from Deuterium at BLAST Aki Shinozaki The latest pion electroproduction results from the BLAST (Bates Large Acceptance Spectrometer Toroid) experiment at the MIT-Bates Linear Accelerator Center are presented. The experiment used the BLAST detector, a longitudinally polarized electron beam at 850 MeV, and internal targets of polarized hydrogen and vector and tensor polarized deuterium. Event selection and particle identification will be discussed. The measured asymmetries for exclusive pion electroproduction from deuterium will be presented and compared with results obtained from hydrogen and available theoretical predictions. [Preview Abstract] |
Sunday, April 15, 2007 12:06PM - 12:18PM |
J16.00009: The Neutron Charge Form Factor at Low $Q^2$ Eugene Geis At the MIT-Bates Linear Accelerator Center, the neutron charge form factor $G_{E}^{n}$ has been measured by means of quasielastic scattering of polarized electrons from vector-polarized deuterium $^{2}\vec H(\vec e,e^{\prime}n)p$. The experiment used the longitudinally polarized, stored electron beam of the MIT-Bates South Hall Ring along with an isotopically pure, highly polarized internal deuterium target provided by an atomic beam source. The measurements have been carried out with the symmetric Bates Large Acceptance Spectrometer Toroid (BLAST) detector with enhanced neutron detection capability. From the beam-target double polarization asymmetry with the target spin oriented perpendicular to the momentum transfer the form factor $G_{E}^{n}$ is extracted over a range of four-momentum transfer, $Q^{2}$, between 0.1 and 0.55 (GeV/c)$^2$ with minimized systematic errors. [Preview Abstract] |
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