Bulletin of the American Physical Society
APS April Meeting 2017
Volume 62, Number 1
Saturday–Tuesday, January 28–31, 2017; Washington, DC
Session Y12: Electromagnetic Interactions |
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Sponsoring Units: DNP Chair: Phillippe Markel, J. G. Univ. Mainz Room: Roosevelt 4 |
Tuesday, January 31, 2017 1:30PM - 1:42PM |
Y12.00001: High Precision Measurement of the Neutron Polarizabilities via Compton Scattering on Deuterium at E$_{\gamma}$=65 MeV Mark Sikora The electric ($\alpha_n$) and magnetic ($\beta_n$) polarizabilities of the neutron are fundamental properties arising from its internal structure which describe the nucleon's response to applied electromagnetic fields. Precise measurements of the polarizabilities provide crucial constraints on models of Quantum Chromodynamics (QCD) in the low energy regime such as Chiral Effective Field Theories as well as emerging ab initio calculations from lattice-QCD. These values also contribute the most uncertainty to theoretical determinations of the proton-neutron mass difference. Historically, the experimental challenges to measuring $\alpha_n$ and $\beta_n$ have been due to the difficulty in obtaining suitable targets and sufficiently intense beams, leading to significant statistical uncertainties. To address these issues, a program of Compton scattering experiments on the deuteron is underway at the High Intensity Gamma Source (HI$\gamma$S) at Duke University with the aim of providing the world's most precise measurement of $\alpha_n$ and $\beta_n$. We report measurements of the Compton scattering differential cross section obtained at an incident photon energy of 65 MeV and discuss the sensitivity of these data to the polarizabilities. [Preview Abstract] |
Tuesday, January 31, 2017 1:42PM - 1:54PM |
Y12.00002: Elastic Compton Scattering from 3He Arman Margaryan, Harald W. Griesshammer, Daniel R. Phillips, Bruno Strandberg, Judith A. McGovern, Deepshikha Shukla We study elastic Compton scattering on $^3$He using chiral effective field theory ($\chi$EFT) at photon energies from 60 MeV to approximately 120 MeV. Experiments to measure this process have been proposed for both MAMI at Mainz and the HI$\gamma$S facility at TUNL. I will present the revised results of a full calculation at third order in the expansion ($\mathcal{O}(Q^3)$). The amplitude involves a sum of both one- and two-nucleon Compton-scattering mechanisms. We have recently computed the fourth-order two-nucleon diagrams. The numerical impact they have on the cross-section results will be discussed. I will also present results in which amplitudes used so far are augmented by the leading effects from $\Delta(1232)$ degrees of freedom, a step which has already been performed for the proton and deuteron processes. Both cross sections and doubly-polarized asymmetries will be presented, and the sensitivity of these observables to the values of neutron scalar and spin polarizabilities will be assessed. [Preview Abstract] |
Tuesday, January 31, 2017 1:54PM - 2:06PM |
Y12.00003: Lepton mass effects in elastic lepton-proton scattering beyond the leading order of QED Oleksandr Koshchii, Andrei Afanasev The future MUSE experiment [1] is devised to solve the “Proton Radius Puzzle” by considering simultaneously elastic $e^\pm p$ and $\mu^\pm p$ scattering. This experiment requires a per cent level accuracy in comparison of electron-proton and muon-proton scattering. Our goal is to provide all the relevant radiative corrections calculations for MUSE without using ultrarelativistic ($m_l \rightarrow 0$) approximation. This approximation is not applicable for the scattering of muons in kinematics of MUSE. In this talk, we will present our up-to-date results on radiative corrections calculations obtained by using a Monte Carlo generator ELRADGEN [2] modified to treat the lepton mass effects with no ultra-relativistic approximation. Next, we will discuss our estimations of the important helicity-flip contribution represented by a scalar $\sigma$ meson exchange in the $t$-channel [3]. This term vanishes in the ultra-relativistic and/or one-photon exchange approximation, and makes a difference in comparison of electron vs muon scattering in MUSE. [1] R. Gilman, E. J. Downie, G. Ron, et al. (MUSE Collab.), e-print arXiv:1303.2160. [2] I. Akushevich, O.F. Filoti, A. Ilyichev, N. Shumeiko, Comp. Phys. Comm. 183, 1448 (2012) [3] O.Koshchii, A.Afanasev, e-print arXiv:1608.01991 [Preview Abstract] |
Tuesday, January 31, 2017 2:06PM - 2:18PM |
Y12.00004: Beam particle tracking for MUSE Anusha Liyanage The proton radius puzzle is the $\sim$7$\sigma$ disagreement between the proton radius extracted from the measured muonic hydrogen Lamb shift and the proton radius extracted from the regular hydrogen Lamb shift and elastic ep scattering form factor data. So far there is no generally accepted resolution to the puzzle. The explanations for the discrepancy include new degrees of freedom beyond the Standard Model. The MUon Scattering Experiment (MUSE) will simultaneously measure ep and $\mu$p scattering at the Paul Scherrer Institute, using the $\pi$M1 beam line at 100-250 MeV/c to cover a four-momentum transfer range of $Q^2$=0.002-0.07 (GeV/c)$^2$. Due to the large divergence of the secondary muon beam, beam particle trajectories are needed for every event. They are measured by a Gas Electron Multiplier (GEM) tracking telescope consisting of three 10x10 cm2 triple-GEM chambers. Fast segmented scintillator paddles provide precise timing information. The GEM detectors, their performance in test beam times, and plans and milestones will be discussed. This work has been supported by DOE DE-SC0012589 and NSF HRD-1649909. [Preview Abstract] |
Tuesday, January 31, 2017 2:18PM - 2:30PM |
Y12.00005: Precision Measurement of the Proton Elastic Cross Section at High $Q^{2}$ Longwu Ou The measurement of proton electromagnetic form factors (FF) is a powerful way to understand the internal structure of proton and gain insight into the nature of the strong interaction. Current data of FF at high $Q^{2}$ have large statistical and systematic uncertainties, which translate into large uncertainties in the extracted cross section in this kinematic range. The GMp experiment in Hall A at Jefferson Lab, starting from 2014, performed precision measurements of elastic \textit{ep} scattering cross section in the $Q^{2}$ range from 7 to 14 $(\textrm{GeV}/c)^{2}$. These measurements will improve the precision on the cross section in the covered $Q^{2}$ range to about $2\%$. They represent a great complement to the world's cross section data set and will be key inputs for future electromagnetic form factor experiments at similar kinematics. In this talk, the instrumentation and techniques used in the experiment will be described, and the current status of the analysis will be presented. [Preview Abstract] |
Tuesday, January 31, 2017 2:30PM - 2:42PM |
Y12.00006: Measurement of the elastic e-p cross-sections at Q$^{\mathrm{2\thinspace }}=$ 0.66, 1.10, 1.51and 1.65 GeV$^{\mathrm{2}}$ Yang Wang The GMp experiment aims to improve the precision on the elastic e-p cross-sections measurement down to below 2{\%} with high momentum transfers Q$^{\mathrm{2\thinspace }}$up to 14 GeV$^{\mathrm{2}}$. The measurement will be critically important to be the benchmark for future cross section measurement at high Q$^{\mathrm{2}}$ and will be very useful to extract the proton's magnetic from factor. In the fall 2015, the GMp collaboration took data at four Q$^{\mathrm{2\thinspace }}$points of 0.66, 1.10, 1.51and 1.65 GeV$^{\mathrm{2\thinspace }}$and in the fall 2016, we plan to take data with Q$^{\mathrm{2}}$ up to 12 GeV$^{\mathrm{2}}$. The cross section measurements at the four low Q$^{\mathrm{2\thinspace }}$points will provide cross check with the existing world data. In this talk, the cross section analysis at the four low Q$^{\mathrm{2\thinspace }}$points will be presented. [Preview Abstract] |
Tuesday, January 31, 2017 2:42PM - 2:54PM |
Y12.00007: Multi-Nucleon Short-Range Correlation Model for Nuclear Spectral Functions. Oswaldo Artiles, Misak Sargsian We develop a theoretical model for~ nuclear~ spectral functions at high missing momenta~ and energies based on the~ multi-nucleon short-range correlation(SRC) model aimed at probing~nuclear structure at short-distances.~The model is based on the effective Feynman diagram method which allows us to account for the~relativistic effects~ in the SRC domain. We derive the contribution of two-nucleon SRC with center of mass motion, and three-nucleon SRCs to the nuclear spectral functions.~The spectral functions are based on two~ theoretical approaches in evaluating covariant~Feynman diagrams: In the first,~ referred to as virtual nucleon approximation, ~ we~ reduce~ Feynman diagrams to the time~ordered~ non-covariant diagrams~ by evaluating nucleon spectators on the SRC at their positive energy poles,~neglecting~ the contribution from vacuum diagrams.~In the second approach, referred to as light-front~ approximation, we formulate the boost invariant nuclear spectral function on the~ light-front reference frame, on which the vacuum diagrams are suppressed.~Numerical calculations and parametrization of spectral functions and momentum distributions are presented. [Preview Abstract] |
Tuesday, January 31, 2017 2:54PM - 3:06PM |
Y12.00008: Quasielastic Transverse and Longitudinal Response Functions in the range 0.55 GeV/c$\leq \mid \overrightarrow{q}\mid\leq$1.0 GeV/c Michael Paolone In order to determine the Coulomb sum in nuclei, a precision measurement of inclusive electron scattering cross sections in the quasi-elastic region was performed at Jefferson Lab. Incident electrons with energies ranging from 0.4 GeV to 4 GeV scattered from $^{4}He$,$^{12}C$,$^{56}Fe$ and $^{208}Pb$ nuclei at four scattering angles ($15^{\circ},60^{\circ},90^{\circ},120^{\circ}$) and scattered energies ranging from 0.1 GeV to 4 GeV. The Rosenbluth separation method is used to extract the transverse and longitudinal response functions at three-momentum transfers in the range 0.55 GeV/c$\leq \mid \overrightarrow{q}\mid\leq$1.0 GeV/c. The Coulomb Sum is obtained for $^{56}Fe$ and $^{12}C$ ,and compared to predictions. We will discuss the impact of our results on short range nucleon-nucleon correlations and the possible modification of the nucleon electromagnetic properties in the nuclear medium. [Preview Abstract] |
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