Bulletin of the American Physical Society
2021 Fall Meeting of the APS Division of Nuclear Physics
Volume 66, Number 8
Monday–Thursday, October 11–14, 2021; Virtual; Eastern Daylight Time
Session MG: Electroweak Interactions |
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Chair: Rakitha Sanjeewa Beminiwattha, Louisiana Tech; Dien Nguyen,, Jefferson Lab Room: Copley & Kenmore |
Wednesday, October 13, 2021 4:00PM - 4:12PM |
MG.00001: Parity-violating electron scattering and the neutron distribution in 27Al. David S Armstrong Parity-violating elastic electron scattering can be used as a probe of the neutron distributions in nuclei, because the weak charge of the neutron is much larger than that of the proton. The electroweak response of the nucleus is then dominated by the neutrons, and thus the radius of the neutron distribution can be extracted from a measurement of the parity-violating asymmetry. The PREX-2 collaboration has used this technique to recently report [Phys. Rev. Lett. 126, 172502 (2021)] an essentially model-independent determination of the neutron skin in 208Pb. Here we report final results from the Qweak experiment for the parity-violating asymmetry from electron scattering on 27Al, accounting for contributions from non-elastic processes, and discuss the implications for the neutron distribution radius in 27Al. This represents only the second extraction of a neutron radius from parity violation, and provides a valuable check of both theory and experiment in a case where we expect the neutron and proton distributions to have similar radii. |
Wednesday, October 13, 2021 4:12PM - 4:24PM |
MG.00002: Search for Light Neutral Bosons in the TREK/E36 Experiment Dongwi H H Dongwi The Standard Model (SM) represents our best description of the subatomic world and has been very successful in explaining how elementary particles interact under the influence of the fundamental forces. Despite its far reaching success in describing the building blocks of matter, the SM is still incomplete; falling short to explain dark matter, baryogenesis, neutrino masses and much more. The E36 experiment was conducted at J-PARC in Japan, it was designed to test lepton universality, and it has additional sensitivity to search for light U(1) gauge bosons. Of particular interest is the muonic K+ decay channel. Such $U(1)$ bosons could be associated with dark matter or explain established muon-related anomalies such as the muon $g-2$ value, and perhaps the proton radius puzzle. A realistic simulation study was employed for these rare searches in a mass range of 20 MeV$/c^2$ to 110 MeV$/c^2$. Preliminary upper limits for the $A^\prime$ branching ratio $\mathcal{B}r(A^\prime)$ extracted at 95\% CL will be presented. |
Wednesday, October 13, 2021 4:24PM - 4:36PM |
MG.00003: Particle identification in the TREK/E36 experiment at J-PARC Thir Narayan S Gautam The TREK/E36 experiment conducted at J-PARC in Japan aims to test lepton universality by a precise measurement of the ratio of decay widths of the decay channels Κe2 and Κμ2, RK =Γ(Κe2)/Γ(Κμ2), and to search for exotic Κ+ decay modes accompanied by light neutral bosons, by utilizing a Κ+ beam stopped in a scintillating fiber target, a highly segmented CsI(Tl) photon calorimeter covering 75% of 4π, charged-particle tracking through a 12-sector toroidal magnet, and particle identification systems. Since the RK value is of order 10-5, the e+ discrimination from other particles is one of the most important issues. Three independent detection systems: time of flight between TOF1 and TOF2, an aerogel Cherenkov detector (AC), and a lead glass Cherenkov detector (PGC) were used for particle identification (PID). In this talk the status and approach of the PID analysis will be presented. |
Wednesday, October 13, 2021 4:36PM - 4:48PM |
MG.00004: Inelastic Background for CREX Devi L Adhikari The Calcium Radius EXperiment (CREX) took place at Jefferson Lab in Hall A from December 2019 to September 2020 and measured the parity-violating asymmetry (APV) on 48Ca using an electroweak interaction probe. An accurate measurement of this tiny (ppm level) asymmetry requires thorough understanding and control of systematic errors including backgrounds and corrections. One of the potential sources of background event contamination comes from inelastically scattered electrons. Although the first excited state of 48Ca is relatively far away (3.831 MeV) from the ground state, the kinematics of the CREX measurement, combined with the natural fluctuations in the beam energy, make it challenging to efficiently reject unwanted inelastic events. The ~10-4 relative momentum resolution of the Hall A High-Resolution Spectrometers (HRSs), together with monitored precision alignment of the flux-integrating quartz detectors, allows us to geometrically exclude most of the inelastic events from the quartz acceptance. In this talk, we will discuss the inelastic background analysis, corrections, and errors for the CREX APV measurement. |
Wednesday, October 13, 2021 4:48PM - 5:00PM |
MG.00005: Evaluating the Certainty of Beam Motion Corrections in High-rate Asymmetry Measurements Cameron S Clarke The Calcium Radius Experiment (CREX) is a precise measurement of the parity violating asymmetry (APV) in polarized elastic electron-nucleus scattering, which successfully ran in Jefferson Lab's Hall A in 2020. In order to achieve the proposed few % precise APV measurement it is necessary to measure and correct for random and helicity correlated motion of the incident electron beam. The experimental collaboration has built upon the experience of previous parity violating electron scattering experiments, allowing for careful evaluation of sources of uncertainty. We will report on the analysis techniques used for correcting the measured beam motion to achieve the precise asymmetry measurement. |
Wednesday, October 13, 2021 5:00PM - 5:12PM |
MG.00006: Correcting for helicity-correlated beam parameters in the parity-violating electron scattering experiment of CREX at Jefferson Lab. Victoria Owen
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Wednesday, October 13, 2021 5:12PM - 5:24PM |
MG.00007: Smart Tessellated Look-up Tables for Nuclear Femtography Mitchell R Kerver, Charles E Hyde, Spyridon Tsalikis, Nikos Chrisochoides Deep Virtual Exclusive Scattering enables construction of spatial images of the quarks and gluons in atomic nuclei. The complexity of these reactions necessitates extensive simulations of the functional behavior of the cross-section. The cross-section can be parameterized by a set of functions called Compton Form Factors (CFFs). In the absence of ab-initio calculations of CFFs from QCD, we must rely on models of experimental data. The computational cost of calculating CFFs can be reduced by interpolating on lookup tables. We utilize the ODU Center for Real-Time Computing software to create a tessellated database of CFFs. Unstructured tessellations provide a discretization of the phase-space using irregular simplices. Tessellations are able to capture the non-uniform characteristics of the functions by concentrating more points in areas that require higher granularity, while still creating fewer number of vertices overall. An iterative adaptivity algorithm was designed to efficiently refine the tessellations to ensure interpolation error is minimized. These utilities provide a flexibility for any model; greatly reducing computation requirements and increasing data portability while maintaining an rms error ~1% between interpolation and model. |
Wednesday, October 13, 2021 5:24PM - 5:36PM |
MG.00008: Vector Analyzing Power Measurements During PREX-II Ryan Richards I report on various 1 GeV measurements of the vector analyzing power $A_{n}$ on spin-0 during PREX-II at $$ = 0.0064 $(\frac{GeV}{c})^{2}$ and $<\theta>$ = $5^{o}$. The PREX-II experiment at Jefferson Lab measured the parity-violating (PV) asymmetry of elastically scattered longitudinally polarized electrons off an unpolarized $^{208}{Pb}$ target. The analyzing power couples to any residual transverse beam polarization thus making it a potential source of systematic error. Dedicated $A_{n}$ measurements were taken highlighted by the first $A_{n}$ measurement on an intermediate Z nuclei, $^{40}{Ca}$. The $^{40}{Ca}$ measurement is interesting as it provides input on the Z dependence of the analyzing power. Additional measurements on $^{208}{Pb}$ and $^{12}{C}$ were taken with the latter being taken since the lead target is sandwiched between two diamond foils. |
Wednesday, October 13, 2021 5:36PM - 5:48PM |
MG.00009: CREx Vector Analyzing Power Measurements Robert W Radloff In elastic electron nucleus scattering where the electron's polarization is perpendicular to its momentum, a vector analyzing power is proportional to the imaginary component of the two photon exchange process. The analyzing power was measured for 40Ca, 48Ca, 208Pb, and 12C using a 2.2 GeV electron probe. Calcium provides a useful insight into intermediate nuclei to fill the gap in experimental data between Aluminum and Lead. An updated discussion of uncertainties and results will be shown. |
Wednesday, October 13, 2021 5:48PM - 6:00PM |
MG.00010: The CREX Acceptance Function Weibin Zhang The CREX experiment measures the parity violating asymmetry of longitudinally polarized electrons scattered from the unpolarized Ca48 nucleus. While measuring one average asymmetry value over a limited spectrometer acceptance, it is the acceptance function that connects what we measured and what theoretical models predict. This means that using the acceptance function for the experiment is crucial to enable proper benchmarking of theoretical models. The acceptance function is constrained by all optical components between the target and the detectors. With a carefully calibrated simulation, a Monte Carlo technique is used to derive the acceptance function. In this talk, I will show how to get the acceptance function in detail and the final result we get for CREX. |
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