Bulletin of the American Physical Society
2012 Fall Meeting of the APS Division of Nuclear Physics
Volume 57, Number 9
Wednesday–Saturday, October 24–27, 2012; Newport Beach, California
Session FB: Electromagnetic Interactions |
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Chair: Douglas Beck, University of Illinois at Urbana-Champaign Room: Plaza II |
Thursday, October 25, 2012 4:00PM - 4:12PM |
FB.00001: Preliminary Results of T and F Asymmetries for $\pi^0$ Photoproduction from the Proton Ross Tucker Polarization observables are an imporant tool for understanding and clarifying baryon resonance spectra. Recently, experiments were conducted at Jefferson Lab using a polarized photon beam incident on a polarized frozen spin target (FROST). We present preliminary data of the $T$ and $F$ asymmetries for $\pi^0$ meson photoproduction from the proton, along with comparisons to theoretical predictions. The data used in the present analysis were taken during the second running period of FROST using the CLAS detector at Jefferson Lab, which utilized transversely polarized protons in a butanol target and an incident tagged photon energy between 0.62 and 2.93 GeV. The $T$ asymmetry is the observable related to transverse target polarization and the world database currently contains 398 such measurements. The $F$ asymmetry is a double-polarization observable that requires circular beam polarization in addition to transverse target polarization. There have been no published measurements of $F$. [Preview Abstract] |
Thursday, October 25, 2012 4:12PM - 4:24PM |
FB.00002: ABSTRACT WITHDRAWN |
Thursday, October 25, 2012 4:24PM - 4:36PM |
FB.00003: ABSTRACT WITHDRAWN |
Thursday, October 25, 2012 4:36PM - 4:48PM |
FB.00004: The Heavy Photon Search Experiment: Searching for Dark Photons at Jefferson Laboratory Omar Moreno The Heavy Photon Search (HPS) is an experiment at Jefferson Lab which will search for heavy $U(1)$ vector bosons in the mass range of 20 MeV/c$^2$ to 1 GeV/c$^2$. These ``heavy photons'' or ``dark photons'' are expected on very general theoretical grounds and are motivated by recent astrophysical evidence suggesting they may mediate dark matter annihilations and/or interactions with ordinary matter. The dark photon couples to the ordinary photon through kinetic mixing which induces their weak coupling to electrons. Since they couple to electrons, dark photons are radiated in electron scattering and can subsequently decay to narrow $e^+$ $e^-$ resonances which can then be observed above the dominant QED Trident background. For suitably small couplings, dark photons travel detectable distances before decaying, providing a second signature. Using Jefferson Lab's high luminosity electron beam along with a compact large acceptance forward spectrometer, silicon vertex tracker, PbWO$_4$ electromagnetic calorimeter and a muon detector, HPS will explore a large and unexplored domain in the mass/coupling plane with extraordinary sensitivity. In this talk, I will review the motivations driving the searches for dark photons and give an overview of the HPS experiment. [Preview Abstract] |
Thursday, October 25, 2012 4:48PM - 5:00PM |
FB.00005: Measurement of the Spin Asymmetries of the Proton Mark Jones The Spin Asymmetries of the Nucleon Experiment (SANE) measured the parallel, $A_\parallel$, and near-perpendicular, $A_{80}$, double spin asymmetries of the proton in inclusive electron scattering. Longitudinally polarized electrons were scattered from an ammonia target which provided polarized protons via dynamic nuclear polarization. The scattered electrons were detected using the Big Electron Telescope Array, BETA, which was centered at 40$^\circ$ and covered a large solid angle. BETA consisted of a scintillator hodoscope, gas Cherenkov, lucite hodoscope and a large array of lead glass detectors. The data was taken at the Thomas Jefferson National Accelerator Facility's Hall C at beam energies of $4.7$ and $5.9~GeV$ and covered $2.5~GeV^2 < Q^2 < 6.5~GeV^2$. From the $A_\parallel$ and $A_{80}$ measurements, the proton's spin asymmetries, $A_1$ and $A_2$, and the spin structure functions of the proton, $g_1$ and $g_2$, can be extracted. The measurements are in a range of Bjorken $x$, $0.3 < x < 0.8$, where extraction of the twist three matrix element $d_2^p $ (an integral of $g_1$ and $g_2$ weighted by $x^2$) is most sensitive. [Preview Abstract] |
Thursday, October 25, 2012 5:00PM - 5:12PM |
FB.00006: \boldmath{$^4He(e,e'p)X$ at $Q^2=2 (GeV/c)^2$ and $x_B=1.24$} Sophia Iqbal, Konrad Aniol, Fatiha Benmokhtar, Javier Rodriguez Vignote A detailed study of the $^4He(e,e'p)^3H$ reaction at large $Q^2$ and Bjorken x reveals a striking dependence of the shape of the missing energy spectrum on the missing momentum. A realistic simulation using only the kinematical constraints of the high resolution spectrometers(HRS) in Hall A of Jefferson Lab gives a very poor representation of the shape of the missing energy spectrum for the triton ground state. The large acceptances of the HRS yields a simulated width of 13 MeV for the $^3H$ ground state compared to an experimental width of 6 MeV. A significant improvement in the shape of the simulated spectrum with the data is achieved when dynamical relativistic theoretical cross sections are included in the simulation. Spectrum shapes and cross sections as a function of missing momentum will be compared to theoretical models using relativistic mean field wave functions for $^4He$ and $^3H$. [Preview Abstract] |
Thursday, October 25, 2012 5:12PM - 5:24PM |
FB.00007: New results on the the nuclear dependence of the EMC effect at large $x_{B}$ Aji Daniel Protons and neutrons are complex bound states of quarks and gluons, held together by the strong interactions of quantum chromo dynamics (QCD). Their structure may be modified inside of the dense environment of a nucleus. Detailed study of the modification of hadron properties in the nuclear environment provide a wealth of information on the nature of QCD. These modifications (known as the EMC effect) have been extensively studied, since the European Muon Collaboration discovered in 1983 that the structure functions and thus the quark distributions in nuclei are modified compared to those of free nucleons. Jefferson lab experiment E03-103 was designed for a precision measurement of the EMC effect in light nuclei, where reliable calculations can be performed, and to improve the precision on the EMC ratio of medium to heavy nuclei. Results from this experiment suggest that the nuclear dependence of the high $x_{B}$ quark distribution may depend on the local nuclear environment, rather than being a purely bulk effect. In this talk, I will discuss the new results from the E03103 experiment and the insights being obtained to the cause of the EMC effect from these studies. [Preview Abstract] |
Thursday, October 25, 2012 5:24PM - 5:36PM |
FB.00008: Strong fields and QED as function of the g-factor Johann Rafelski, Lance Labun Precision QED experiments (muon $g-2$ and Lamb shift) require understanding of QED with arbitrary gyromagnetic ratio $g>2$. We will first show that the need to have a renormalizable theory requires for $g>2$ reformulation in terms of Klein-Gordon-Pauli (KGP) equation. Using KGP, we obtain the nonperturbative effective action of QED within Schwinger proper time method in arbitrarily strong quasi-constant external electromagnetic fields as a function of $g$. The expression is divergent for $|g|>2$, given the magnetic instability of the vacuum due to the lowest Landau orbit eigenenergy having an indefinite value in strong magnetic fields. The spectrum of Landau eigenvalues for KGP in a magnetic field is an exact periodic function of $g$, no states are disappearing from the spectrum. This periodicity allows to establish a generalized form of the effective action valid for all $g$. We show the presence of a cusp at the periodic points $g=\ldots-6,-2,2,6\ldots$. Consequently, the QED beta function and parts of light-by-light scattering differ from perturbative computation near to $g=2$ and an asymptotically free domain of $g$ for QED arises. We further show that only for $g=(2N+1)$ there is exact correspondence of a field-dependent quasi-temperature and the Unruh Temperature. [Preview Abstract] |
Thursday, October 25, 2012 5:36PM - 5:48PM |
FB.00009: An Approximate Method for Calculation of Coulomb Distortion in Electron Scattering by use of Partial Wave Expansions Dan Kosik I will present a new approach to calculations of electron scattering reactions that include Coulomb Distortion by numerically solving for the relativistic radial wave functions for a simple nuclear charge distribution and setting the normalization and phase by comparison to Bessel functions in a plane wave expansion outside of the nucleus. Calculations for a surface nuclear transition density will be discussed and its implications for calculations of cross sections for inelastic scattering around 400 MeV that include Coulomb Distortion. [Preview Abstract] |
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