Bulletin of the American Physical Society
2013 Fall Meeting of the APS Division of Nuclear Physics
Volume 58, Number 13
Wednesday–Saturday, October 23–26, 2013; Newport News, Virginia
Session NB: Electroweak Interactions II |
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Chair: David Mack, Thomas Jefferson National Accelerator Facility Room: Pearl Ballroom I |
Saturday, October 26, 2013 8:30AM - 8:42AM |
NB.00001: Charge Symmetry Breaking and Parity Violating Electron Scattering Gerald A. Miller I review the effects of charge symmetry breaking CSB on electromagnetic form factors and how that influences extraction of information regarding nucleon strangeness content and the weak mixing angle. The use of observed CSB in nucleon-nucleon interactions is used to constrain earlier calculations that found significant uncertainty due to CSB effects. A new relativistic chiral perturbation theory calculation of the CSB effects of pion clouds, driven by the difference between nucleon masses is present. It seems that CSB effects are very modest and should not impact the analysis of experiments. [Preview Abstract] |
Saturday, October 26, 2013 8:42AM - 8:54AM |
NB.00002: The $Q_{\mathrm{weak}}$ Experiment: Measurement of the Elastic Parity-Violating e-p Asymmetry at Low Q$^{2}$ Adesh Subedi Q-weak part 1. The $Q_{\mathrm{weak}}$ experiment at Jefferson laboratory has measured the parity-violating asymmetry in e-p elastic scattering at Q$^{2} =$ 0.025 (GeV/c)$^{2}$, employing longitudinally polarized electrons incident on a 34.5 cm long liquid hydrogen target. The measurement was performed using an integrating mode apparatus with a set of eight quartz Cerenkov detectors placed radially along the beam axis. The resulting measured asymmetry is then corrected for various effects, including false asymmetries generated by helicity-correlated beam properties, backgrounds from aluminum target windows and the beamline, and the beam polarization. The results of the experiment's commissioning run will be reported, which consist of approximately 1/25$^{\mathrm{th}}$ of the total data collected during the full measurement. This talk will focus on the $Q_{\mathrm{weak}}$ apparatus and the analysis to determine the asymmetry. A value of the physics asymmetry from the experiment's commissioning run will be presented. [Preview Abstract] |
Saturday, October 26, 2013 8:54AM - 9:06AM |
NB.00003: The Qweak Experiment: First Determination of the Weak Charge of the Proton Scott Macewan Qweak part 2: The Qweak experiment at Jefferson Lab uses parity-violating electron scattering to make a precision measurement of the proton's weak charge. The experiment has recently reported a measurement of the asymmetry in $\overline{e}-p$ scattering at low $Q^2$ = 0.0250 GeV/c$^2$ based on approximately 1/25 of the overall data collected in the experiment. The small $Q^2$ of the measurement has made possible the first determination of the weak charge of the proton, $Q^p_W$, by incorporating this new measurement with earlier parity violating electron scattering data at higher $Q^2$ to obtain hadronic corrections. The details of the analysis required to extract $Q^p_W$ and its error from the measured asymmetry will be presented. [Preview Abstract] |
Saturday, October 26, 2013 9:06AM - 9:18AM |
NB.00004: The Q-weak Experiment: Implications from the First Determination of the Proton's Weak Charge Joshua Magee $Q_{weak}$ part 3: The $Q_{weak}$ experiment recently completed data taking at Jefferson Laboratory with the aim of making the first experimental determination of the proton's weak charge, the neutral-weak analog of the electric charge. Results have been obtained from the first period of data-taking, which comprises 3 days of beam and 4\% of the total data set. The experiment measured the small parity-violating asymmetry of elastic electron-proton scattering, which allows direct extraction of $Q_W^p$. Once extracted, the current results directly probe potential new parity-violating semi-leptonic physics beyond the Standard Model at the $TeV$ scale. For the general 4-fermion contact interaction, the probed mass-limit is ~1.1 $TeV$ with 95\% confidence. When combined with the world's parity-violating data, extraction of the neutron's neutral-weak charge, $Q_n^p$, and the individual quark weak vector couplings, $C_{1u}$ and $C_{1d}$, are also possible. This talk will focus on the implications of the current $Q_{weak}$ experimental results, including the extraction of the proton and neutron weak charges, the quark weak couplings, and also highlight the mass-limit reach of Standard Model extensions probed. Projections to the final $Q_{weak}$ dataset will be provided. [Preview Abstract] |
Saturday, October 26, 2013 9:18AM - 9:30AM |
NB.00005: Parity Violating Asymmetry in Elastic e-Al Scattering Joshua Hoskins The \(Q_{weak}\) Experiment, which completed running May 2012 at Jefferson Lab, will provide the first direct measurement of the proton's weak charge, \(Q_{w}^p\) , by measuring the parity-violating asymmetry in elastic electron-proton scattering. In order to meet experimental goals, we must understand and precisely measure backgrounds which contribute to the experimental asymmetry. The most significant background contribution comes from elastic and quasielastic electron-aluminum scattering from the target windows, which constitutes a roughly 30\% correction to the experimental asymmetry. Our data will provide the first measurement of the small (few parts-per-million) parity-violating asymmetry from aluminum. An overview of the experimental approach, data quality, and projected error will be given. [Preview Abstract] |
Saturday, October 26, 2013 9:30AM - 9:42AM |
NB.00006: Parity-Violating Asymmetry in the N $\to\Delta$ Transition Anna Lee The primary focus of the recently completed $Q_{\mathrm{weak}}$ experiment at Jefferson Lab is the determination of the proton's weak charge. To properly make corrections to the measured asymmetry, dedicated measurements were made of the parity-violating asymmetry at low $Q^2$ in inelastic $\vec{e}$-p scattering at the N $\to\Delta$ transition for two different beam energies. The asymmetries are used to extract an additional physics result, the low energy constant d$_\Delta$, which is responsible for the Siegert term that causes the asymmetry to be non-zero even at the photon point ($Q^2$=0). The d$_\Delta$ term is a measure of the hadronic parity violation in this transition. It has been shown to be related to some puzzles in radiative hyperon decays. These analyses suggest potential values of d$_\Delta$ much larger than its natural scale. The measurements described here were done at beam energies of 877 MeV ($Q^2$ = 0.011 GeV$^2$) and 1165 MeV ($Q^2$= 0.021 GeV$^2$) using the $Q_{\mathrm{weak}}$ apparatus. An overview of the motivations for the measurement, the experimental approach, and the status of the analysis will be presented. [Preview Abstract] |
Saturday, October 26, 2013 9:42AM - 9:54AM |
NB.00007: Parity-Violating Inelastic $\vec{e}p$ Asymmetry and Its Relation to $\gamma Z$ Box Radiative Corrections James Dowd The Qweak Experiment at Jefferson Lab will make the first direct measurement of the proton's weak charge, $Q_W^p$, via a measurement of the parity-violating asymmetry in elastic electron-proton scattering with low four-momentum transfer. To reach the precision goal of Qweak, energy dependent radiative corrections in the parity-violating asymmetry must be accounted for. The most significant of these is the $\gamma Z$ box diagram. The asymmetry arising from this diagram depends on the $\gamma Z$ interference structure functions, $F_{1,3}^{\gamma Z}$, for which there is almost no experimental data. Using the Qweak apparatus, with modifications, an ancillary measurement was taken at a higher beam energy of 3.35 GeV. The chosen kinematics accesses inelastic scattering, where the asymmetry depends on these structure functions, allowing tests of their theoretical description. Additions to the Qweak apparatus include a lead wall in front of one of the eight Cerenkov detectors to isolate the pion background in the asymmetry measurement, as well as a dedicated lead glass pion detector. Analysis of this data will lead to an improved determination of the $\gamma Z$ box contribution to the proton's weak charge, thereby validating the theoretical models used to predict this contribution. [Preview Abstract] |
Saturday, October 26, 2013 9:54AM - 10:06AM |
NB.00008: Beam Normal Single Spin Asymmetries in Elastic Electron Scattering from Selected Targets Wade Duvall The primary focus of the $Q_{\mathrm{weak}}$ experiment at Jefferson Lab is the determination of the proton's weak charge. To make corrections to the measured asymmetry, dedicated measurements were made of the parity-conserving beam normal single spin asymmetries ($A_{\mathrm{n}}$) in elastic scattering of transversly polarized electrons from several unpolarized targets. The targets included hydrogen, carbon, and aluminum. In the case of hydrogen, two separate spectrometer settings were used to study elastic scattering off both the protons and electrons in the hydrogen target. The $A_{\mathrm{n}}$ for the hadronic targets are dominated by two-photon exchange amplitudes, which were important in resolving the discrepancy between two different methods determining the proton's electromagnetic form factors. For the heavy nuclear targets, proper calculation of Coulomb distortion effects are also important. For the case of the elastic scattering from electrons (Moller scattering), the asymmetry is a calculable QED process. The measurements were made with the $Q_{\mathrm{weak}}$ apparatus at a beam energy of 1165 MeV and central scattering angle of $\sim 8^\circ$. An overview of the motivations, the experimental approach, and the status of the analysis will be presented. [Preview Abstract] |
Saturday, October 26, 2013 10:06AM - 10:18AM |
NB.00009: Beam Normal Single Spin Asymmetry in the N-to-Delta Transition Nuruzzaman Nuruzzaman The Q-weak experiment in Hall C at the Thomas Jefferson National Accelerator Facility has made the first direct measurement of the weak charge of the proton, Q$^{\mathrm{p}}_{\mathrm{W}}$, through the precision measurement of the parity-violating (PV) asymmetry in elastic e-p scattering at low momentum transfer. The data are currently under analysis. There is a parity conserving Beam Normal Single Spin Asymmetry or transverse asymmetry (A$_{\mathrm{n}})$ on H$_{2}$ with a sin($\varphi )$-like dependence due to 2-$\gamma $ exchange. The size of A$_{\mathrm{n}}$ is few ppm, so a few percent residual transverse polarization in the beam, in addition to potentially small broken azimuthal symmetries in the detector, might lead to few ppb corrections to the Q-weak data. As part of a program of A$_{\mathrm{n}}$ background studies, we made the first measurement of A$_{\mathrm{n}}$ in the N-to-Delta transition using the Q-weak apparatus. A$_{\mathrm{n}}$ from electron-nucleon scattering is also a unique tool to study the $\gamma $*$\Delta \Delta $ form factors [1]. Status of the analysis will be presented.\\[4pt] [1] C. Alexandrou et. al, http://arxiv.org/abs/0901.3457v1. [Preview Abstract] |
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