Bulletin of the American Physical Society
APS April Meeting 2011
Volume 56, Number 4
Saturday–Tuesday, April 30–May 3 2011; Anaheim, California
Session L10: Mini-symposium on Parity Violation III |
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Sponsoring Units: DNP Chair: David Armstrong, Thomas Jefferson National Accelerator Facility Room: Garden 1 |
Sunday, May 1, 2011 3:30PM - 3:42PM |
L10.00001: Measuring Neutron Densities with Parity Violating Electron Scattering Charles Horowitz, Shufang Ban, Robert Michaels Parity violating electron scattering provides a model independent probe of neutron densities because the weak charge of a neutron is much larger than the weak charge of a proton. We estimate required beam time to measure the neutron radius or neutron skin thickness for a variety of nuclei. Lighter nuclei such as 48Ca require significantly less beam time than heavier nuclei such as 208Pb because they can be measured with higher momentum transfers where the parity violating asymmetry is larger. We review the large implications of neutron density measurements for nuclear structure, including three neutron forces, and for astrophysics, including the equation of state of neutron rich matter. [Preview Abstract] |
Sunday, May 1, 2011 3:42PM - 3:54PM |
L10.00002: Relativistic effective interaction for nuclei, giant resonances, and neutron stars Farrukh J. Fattoyev, Charles J. Horowitz, Jorge Piekarewicz, Gang Shen A new relativistic effective interaction that is simultaneously constrained by the properties of finite nuclei, their collective excitations, and neutron star properties is introduced. It is shown that by adjusting two of the empirical parameters of theory, one can efficiently tune the neutron thickness of $^{208}Pb$ and the maximum mass of the neutron star. This new effective interaction referred to as the IU-FSU interaction, is fitted to a modest neutron thickness of $R_n- R_p = 0.16$ fm in $^{208}Pb$ and a moderate maximum neutron star mass of $M_{max} = 1.94 M_{Sun}$. [Preview Abstract] |
Sunday, May 1, 2011 3:54PM - 4:06PM |
L10.00003: Transverse Asymmetries from Nuclei in Electron Scattering Robert Michaels Measurements at Jefferson Lab of the transverse asymmetry $A_T$ in few-GeV electron scattering from various nuclei at forward angles will be presented. The electron's spin is polarized transverse to its momentum. The asymmetry arises from the interference of one-photon and two-photon exchange and is a potentially important systematic for parity-violating electron scattering experiments. The nuclei measured are H, ${}^2$H, ${}^4$He, ${}^{12}$C, and ${}^{208}$Pb at corresponding kinematics ($E$, $\theta$) (GeV, degrees) = (3.18, 6), (6.06, 13), (2.75, 6), (1.05, 5) and (1.05, 5). The asymmetries are a few parts per million (ppm) and will be compared to available theoretical calculations. [Preview Abstract] |
Sunday, May 1, 2011 4:06PM - 4:18PM |
L10.00004: FADC DAQ/Analysis Zafar Ahmed This talk presents an introduction to the Flash ADC Data Acquisition(FADC DAQ) system for Moller polarimetry in Hall A of Thomas Jefferson National Accelerator Facility. The Moller polarimeter measures the beam polarization to high precision to meet the specification of the PREx(Lead radius experiment), which plans to measure the neutron radius in lead with a 1{\%} error. The FADC DAQ is part of the upgrade of Moller polarimetery to reduce the systematic error for PREx. The first half of this talk is about hardware setup and the second half covers the results of the analysis. [Preview Abstract] |
Sunday, May 1, 2011 4:18PM - 4:30PM |
L10.00005: PREX Instrumentation Luis Mercado The Lead Radius Experiment (PREx) took place in the Spring of 2010 at the Thomas Jefferson National Accelerator Facility. Its goal was to obtain a clean measurement of the root mean square neutron radius of $^{208}$Pb to 1{\%} accuracy. This was done by measuring the parity violating electroweak asymmetry in the elastic scattering of polarized electrons from a Lead target. In order to obtain such a precise measurement, numerous improvements and upgrades were made to the instrumentation and electronics of Hall A. This talk will discuss developments related to the PREx main detectors, Data Acquisition system and Luminosity Monitor. [Preview Abstract] |
Sunday, May 1, 2011 4:30PM - 4:42PM |
L10.00006: Compton Polarimetry Results for the HAPPEX-III Experiment Megan Friend The Hall A Compton polarimeter has been used to make a precise, continuous measurement of the electron beam polarization during HAPPEX-III. The recent upgrade to the Compton photon detector and DAQ, including the implementation of a high brightness GSO crystal and an integrating FADC, have allowed for this 1\% measurement using photon detection alone. The results of this high precision measurement will be presented. [Preview Abstract] |
Sunday, May 1, 2011 4:42PM - 4:54PM |
L10.00007: Development of a non-invasive, continuous polarimeter for Hall C at Jefferson Lab Donald Jones The stringent requirements of the parity violating experimental program at Jefferson Lab necessitate an accurate knowledge of electron beam polarization. In particular, the tight error budget for the Qweak experiment currently in production in Hall C allows an error of only $\pm1\%$ for the measurement of electron beam polarization. In order to achieve this, a Compton polarimeter has been recently built in Hall C and is being utilized as part of the polarimetry program. Compton polarimetry derives its analyzing power from the spin dependence of the $\gamma$-e interaction and requires a highly polarized coherent beam of photons with well known properties. I discuss the development and performance of a resonant optical cavity at a wavelength of 532~nm for use as a photon target and some of the difficulties encountered in the process, as well as the means of determining intra-cavity beam properties. [Preview Abstract] |
Sunday, May 1, 2011 4:54PM - 5:06PM |
L10.00008: Precision Compton Polarimetry for the $Q_{weak}$ Experiment Juan Carlos Cornejo The $Q_{weak}$ experiment currently running in Hall C of Jefferson Lab will measure the electro-weak parity violating asymmetry in the cross sections of elastic electron-proton scattering at an energy of 1.16~GeV and determine the weak mixing angle $\sin^2\theta_W$ at a $Q^2$ of 0.03~GeV$^2$/c$^2$. The largest contribution to the systematic error is the polarization measurement. To limit this uncertainty a new Compton polarimeter was built that will measure the polarization to 1\% at the 1.16~GeV beam energy. The polarization is measured by backscattering a photon off the incoming electron and measuring the asymmetry in the yield for different helicity states. The Compton polarimeter is composed of a four dipole chicane, a green laser cavity, an electron and a photon detector. The photon detector consists of a undoped CsI crystal attached to a photomultiplier. The signals are integrated over a 1~ms long helicity window, and single photon pulses are accepted simultaneously. We are currently taking data in production mode. Preliminary polarization results from the ongoing analysis of the photon detector will be presented. [Preview Abstract] |
Sunday, May 1, 2011 5:06PM - 5:18PM |
L10.00009: The Characterization and Performance of the Luminosity Monitors for the Qweak Experiment at Jefferson Lab John Leacock The $Q_{weak}$ experiment at Jefferson Lab is a precision measurement of the weak charge of the proton using parity-violating electron scattering. To make this measurement the experiment uses diagnostic detectors with small counting statistical errors that provide information about beam and target properties. The $Q_{weak}$ luminosity monitors were designed to provide this information. The luminosity monitors are arrays of quartz \v Cerenkov detectors coupled with air lightguides to photomultiplier tubes operating in unity gain mode and read out in current mode. There are two sets of luminosity monitors, a ``downstream'' array at a mean laboratory scattering angle of 0.5 degrees that detects an equal mixture of elastic e-p and M\o ller scattered electrons and an ``upstream'' array at a mean scattering angle of 5 degrees that primarily detects low energy M\o ller scattered electrons. The monitors can also be equipped with high gain bases to operate in pulse counting mode for use as beam monitors in special low beam current diagnostic runs. The characterization and performance of the luminosity monitors will be presented. [Preview Abstract] |
Sunday, May 1, 2011 5:18PM - 5:30PM |
L10.00010: Beam Modulation Strategy for the Q-weak Experiment F.N.U. Nuruzzaman A new, robust strategy is presented for beam modulation in the Q-weak experiment. The objective of the Q-weak experiment is to measure the weak charge of the proton via the parity violating asymmetry ($<$ 1ppm) in elastic e-p scattering. The e-p scattering rate largely depends on five beam parameters: horizontal position (X), angle (X'), vertical position (Y), angle (Y'), and beam energy (E). Changes in these beam parameters when the beam polarization is reversed will create false asymmetries. Although we will attempt to keep changes in beam parameters during reversal as small as possible, we will also measure beam parameter differences and correct the false asymmetries. To do this, we will modulate X, X', Y, Y' using four air-core dipoles in the Hall C beamline and measure the beam sensitivities. (We will also modulate beam energy using an SRF cavity.) Two air-core dipoles separated by $\sim $10m will be pulsed at a time to produce relatively pure position or angle changes at the target, for virtually any tune of the beamline. Some preliminary tests of the air-core coils, its analysis and the associated control instrumentation will be discussed. [Preview Abstract] |
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