Bulletin of the American Physical Society
2011 Fall Meeting of the APS Division of Nuclear Physics
Volume 56, Number 12
Wednesday–Saturday, October 26–29, 2011; East Lansing, Michigan
Session GC: Electroweak Interactions II |
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Chair: Allena Opper, The George Washington University Room: 101 |
Friday, October 28, 2011 8:30AM - 8:42AM |
GC.00001: The Qweak Experiment: A Search for New Physics at the TeV Scale via a Measurement of the Proton's Weak Charge Rakitha Beminiwattha The \mbox{Qweak} experiment at Jefferson Lab will measure the parity-violating elastic electron-proton scattering asymmetry at $\mathrm{Q^2} \simeq \mathrm{0.03(GeV/c)^2}$ to obtain the weak charge of the proton, $\mathrm{Q^p_W}$, to an accuracy of $\mathrm{4\%}$. The result will test the Standard Model prediction of the running of $\mathrm{\sin^2 \theta_W}$ and will provide an indirect probe of new physics at $\mathrm{TeV}$ scale. An overview and the performance of the experiment after the first data taking run will be provided. [Preview Abstract] |
Friday, October 28, 2011 8:42AM - 8:54AM |
GC.00002: ABSTRACT WITHDRAWN |
Friday, October 28, 2011 8:54AM - 9:06AM |
GC.00003: Measuring the Parity-Violating Asymmetry of Aluminum in the $Q_{weak}$ Experiment Katherine Myers The $Q_{weak}$ Collaboration at Jefferson Lab will perform the first direct measurement of the proton's weak charge, $Q^p_W$, to a precision of 4\% by measuring the parity-violating asymmetry in elastic electron-proton scattering. At tree level, the weak mixing angle is related to the weak charge of the proton by $Q^p_W$=1-4$\sin^2\theta_W$, leading to a 0.3\% measurement of $\sin^2\theta_W$ at low energy. To achieve these goals, systematic effects must be well understood and measured precisely. One of the largest corrections to the experimental asymmetry comes from elastic electron-Aluminum scattering in the target windows. This asymmetry must be measured directly in dedicated thick Aluminum target runs and measured to a relative precision of a few percent. The measurement of this asymmetry will provide the first extraction of the parity-violating elastic electron-Aluminum asymmetry. To extract this asymmetry, corrections for target contaminants (other nuclei present in the Aluminum alloy used), quasielastic scattering, and inelastic transitions must be considered. A discussion of the data quality from the first production run of the experiment as well as the mentioned corrections will be presented. [Preview Abstract] |
Friday, October 28, 2011 9:06AM - 9:18AM |
GC.00004: A Diamond Micro-strip Electron Detector for Compton Polarimetry Amrendra Narayan The Qweak experiment in Hall C at Jefferson Lab aims to measure the weak charge of the proton with a precision of 4.1{\%} by measuring the parity violating asymmetry in polarized electron-proton elastic scattering. Beam polarimetry is the largest experimental contribution to the error budget. A new Compton polarimeter was installed for a non-invasive and continuous monitoring of the electron beam polarization with a goal of 1{\%} systematic and 1{\%} per hour statistical precision. The Compton-scattered electrons are detected in four planes of diamond micro-strip detectors. These detectors are read out using custom built electronic modules that include a pre-amplifier, a pulse shaping amplifier and a discriminator for each detector micro-strip. We use Field Programmable Gate Array based general purpose logic modules for event selection and histogramming. The polarimeter was commissioned during the first run period of the Qweak experiment. We will show the preliminary results from the electron detector obtained during the first run period of Qweak experiment [Preview Abstract] |
Friday, October 28, 2011 9:18AM - 9:30AM |
GC.00005: Simulation and Measurement of the Qweak Main Detector Energy Sensitivity Adesh Subedi The Qweak experiment in Hall C at Jefferson lab aims to make the first direct measurement of the weak charge of the proton with about 4{\%} overall uncertainty by measuring the parity violating asymmetry in elastic electron-proton scattering. Changes in helicity correlated beam properties create false asymmetries, particularly if the apparatus is misaligned. We measure and correct such false asymmetries, but also try to understand and reduce them where possible. This talk will emphasize simulations of the sensitivity of the main detector to energy jitter (the single largest correction!) and what the comparison to data tells us about our detector alignment. [Preview Abstract] |
Friday, October 28, 2011 9:30AM - 9:42AM |
GC.00006: Results from UCNA 2010 Robert Pattie We will present the results of a $\approx 0.7\%$ measurement of the electron momentum neutron spin angular correlation coefficient ``$A$'' using polarized ultracold neutrons (UCN) during the 2010 beam cycle at the Los Alamos Neutron Science Center (LANSCE) by the UCNA collaboration. Improvements made to the solid deuterium ultracold neutron source and the neutron guide system allowed us to achieve the a factor of two increase in the decay rate and overall statistics. Major systematic uncertainties, including detector calibration and linearity, electron backscattering, and neutron polarimetry, were reduced, bringing the full sytematic uncertainty to below $0.6\%$ based on the investigations during the 2008-2009 beam cycles. [Preview Abstract] |
Friday, October 28, 2011 9:42AM - 9:54AM |
GC.00007: UCN Transport Brittney VornDick The UCNA experiment utilizes ultracold neutrons (UCN) to measure angular correlations in beta-decay. UCN are produced in a solid deuterium source and then coupled to the experimental decay volume through a sequence of guide tubes. Requirements for the guides typically include smooth surfaces, high Fermi potentials, and often a very low depolarization probability per bounce. We review the UCNA guide geometry and chacterize the effectiveness of recently developed diamond-like carbon coatings produced by pulsed laser deposition on Cu and quartz tubing. We also describe the development of a UCN shutter to be used to monitor UCN polarization. Finally we present research and development towards new coating processes and materials for UCN guides. [Preview Abstract] |
Friday, October 28, 2011 9:54AM - 10:06AM |
GC.00008: Precision Polarimetry with UCN in the UCNA Experiment A.T. Holley The UCNA experiment, which uses ultracold neutrons (UCN) to determine the angular correlation between the electron momentum and the neutron spin (the beta-asymmetry) in free polarized neutron decay, was developed to provide a complementary technique to cold neutron beam measurements. Neutron polarization is an important systematic in both approaches, especially since neutron spin flippers are generally required to reduce detector-related asymmetries. Traditionally neutron polarimetry in such experiments amounts to an \textit{ex situ} determination of both the polarizing efficiency and the spin flipping efficiency using, for example, a crossed polarizer analyzer apparatus. This technique was applied to the UCNA polarization system, but the use of UCN in the experiment allows for a second \textit{in situ} method of performing polarimetry which serves as the primary monitor of neutron polarization for UCNA. Results from both polarimetry techniques will be compared, and polarimetry data collected during UCNA running through the 2010 run cycle will be presented. [Preview Abstract] |
Friday, October 28, 2011 10:06AM - 10:18AM |
GC.00009: The future of UCNA: towards a sub-0.4\% measurement of the neutron beta decay asymmetry using ultracold neutrons Michael Mendenhall The UCNA experiment uses trapped ultracold neutrons (UCN) to measure the neutron beta decay asymmetry ``$A$''. Since publication of a proof-of-principle result in 2009, a series of improvements have increased the statistical and systematic sensitivity of the experiment, from an initial 4\% determination of $A$ to the 1.4\% result published in 2010 and the soon-to-be-published $\sim$0.7\% measurement. This talk describes plans for pushing the UCNA experiment towards the limits of its sensitivity (below 0.4\%), including higher precision polarimetry and energy calibrations, thinner windows to decrease backscattering and monte carlo corrections, and improvements in UCN production and transport. [Preview Abstract] |
Friday, October 28, 2011 10:18AM - 10:30AM |
GC.00010: Fierz Interference in Beta Decay of Ultracold Neutrons Kevin Hickerson We discuss the status of the UCNb experiment that uses the ultracold neutron (UCN) source at LANSCE. The UCNb apparatus is being designed to test contributions to scalar and tensor interactions from physics beyond the Standard Model, manifest as a nonzero value for the neutron Fierz interference parameter, $b_n = (b_F -3\lambda b_{GT})/(1+3\lambda^2)$, in the $\beta$ energy spectrum of neutron decay. Some models may have $b_n$ as large as $10^{-3}$, but below the current limits on the Fermi component, $b_F$, set by superallowed $0+ \to 0+$ nuclear $\beta$ decays. Neutron decay has the advantage of sensitivity to the Gamow-Teller component of $b$, $b_{GT}$. We present data from UCN test runs from 2010 that help set limits on systematic backgrounds from $\beta$ decay of spallation produced 6He and from UCN generated $\gamma$ backgrounds. We also discuss test plans and upgrades for 2011 and beyond. [Preview Abstract] |
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