Bulletin of the American Physical Society
2020 Fall Meeting of the APS Division of Nuclear Physics
Volume 65, Number 12
Thursday–Sunday, October 29–November 1 2020; Time Zone: Central Time, USA
Session FF: Mini-Symposium: Low Energy Probes of New Physics II |
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Chair: Vincenzo Cirigliano, LANL |
Friday, October 30, 2020 2:00PM - 2:12PM |
FF.00001: Extracting the muon-weighted magnetic field for the Muon $g-2$ experiment Brynn MacCoy The Fermilab Muon $g-2$ experiment is measuring $a_{\mu}$, the anomalous magnetic moment of the muon, to high precision. The previous-generation experiment at Brookhaven National Lab measured a value of $a_{\mu}$ that differs by $3.7{\sigma}$ from the recently published Standard Model compilation White Paper. Results from the Fermilab Run-1 data taking campaign, with an expected precision approximately equal to the final BNL result, are being released soon. To obtain $a_{\mu}$, two measurements are required: the anomalous muon precession frequency ($\omega_{a}$) and the magnetic field ($B$) experienced by the muons in the storage ring. A system of pulsed NMR probes positioned outside the storage region tracks $B$ during physics running, and a trolley carrying 17 NMR probes periodically maps $B$ inside the storage region. To determine the average field used in the $a_{\mu}$ result, the measured $B$ is first weighted by the spatial and temporal distribution of the muon beam, then averaged. Straw trackers reconstruct the beam at two locations in the ring. Dynamic effects change the beam distribution as a function of both azimuth and time. The final analysis of the muon-weighted magnetic field and its sources of uncertainty for Run-1 will be presented. [Preview Abstract] |
Friday, October 30, 2020 2:12PM - 2:24PM |
FF.00002: The Phase-Acceptance Effect in Run 1 of the Fermilab Muon g-2 Experiment Renee Fatemi The Muon g-2 Experiment (E989) at Fermilab is measuring the anomalous magnetic moment of the muon, $a_\mu$, with improved precision compared to the Brookhaven (E821) experiments whose results were found to be inconsistent with the Standard Model. Muons are injected and stored in a circular ring, with a magnetic dipole field and an electrostatic quadrupole system (EQS) providing radial and vertical focusing. During the first full physics run in 2018 the potential on a subset of the plates in the EQS exhibited an unexpected time dependence throughout the muon storage period. This led to a time dependent vertical position and width of the beam, which when coupled with the finite acceptance of the calorimeters, translated directly to a time dependence of the average muon phase (the angle between the muon momentum and spin vectors) at the time of injection. This phase-acceptance effect results in a pull on the extraction of the anomalous precession frequency of the muon and is one of the leading systematic errors associated with the analysis of the run 1 dataset. Techniques used to quantify the pull on $a_\mu$ and associated systematic errors will be discussed. [Preview Abstract] |
Friday, October 30, 2020 2:24PM - 2:36PM |
FF.00003: An energy integrated approach for precession frequency analysis in Muon $g-2$ experiment Ritwika Chakraborty The Muon $g-2$ experiment(E989) at Fermilab aims to measure the anomaly, $a_{\mu}$, in the muon's magnetic moment with an improved precision compared to the previous experiment(E821) at Brookhaven whose results were found to be inconsistent with the Standard Model. We discuss a new approach to the measurement of the muon's anomalous precession frequency that is used in the determination of the anomaly. This new "energy-integrating" approach involves constructing the time distribution of energy deposited by the decay positrons in the electromagnetic calorimeters in contrast to counting individual positrons as done in traditional analyses approaches. The energy-integrating approach has advantages over positron-counting approaches in terms of systematics effects arising from gain changes and pulse pileup. This talk will present an overview of the energy integrated approach and provide a summary of the analysis of the run-1 dataset using this method. A status update on the energy integrated analysis of the subsequent datasets will also be discussed. [Preview Abstract] |
Friday, October 30, 2020 2:36PM - 2:48PM |
FF.00004: Search for Physics Beyond the Standard Model at the Jefferson Lab Eta Factory. Igal Jaegle The Hall D Jefferson Lab Eta Factory (JEF) will collect data with the GlueX apparatus and an upgraded Forward Calorimeter (FCAL-II), which consists of a 1 m$^2$ PbWO$_4$ crystal insert in the central region of the existing FCAL. The JEF Beyond the Standard Model (BSM) physics program will search for sub-GeV dark gauge bosons (vectors, scalars, axion-like pseudo-scalars) up to 1~GeV/${\it c}^2$ in the $\eta$ and $\eta'$ decays or direct photoproductions. Some of the JEF BSM search channels and the experimental sensitivities will be discussed. [Preview Abstract] |
Friday, October 30, 2020 2:48PM - 3:00PM |
FF.00005: Seeking a Fifth Force with DarkLight Ross Corliss In addition to cosmic motivations, anomalies in precision nuclear and atomic measurements have prompted standard model extensions in the form of Dark Photons or, more generically, a new force-carrier. Existing experimental searches for such particles have probed the majority of the parameter space of simple models, but so far no culprit has been found and the standard-model anomalies remain unexplained. The recent report of anomalous correlations in $^4$He transitions, joining a similar anomaly in $^8$Be, has heightened interest in a potential new particle near 17MeV. Although this region has been partially explored via hadronic production mechanisms, a particle with proto-phobic couplings is more effectively probed using leptonic production. The DarkLight experiment proposes to search for this particle ($A'$) in electron-nuclear scattering via the process $e^-X\rightarrow e^-XA'\rightarrow e^-Xe^+e^-$. I will give a brief review of motivations for the search and discuss the DarkLight proposal to install a spectrometer pair at Jefferson Lab's CEBAF Injector to search for this new particle, as well as prospects for future searches at high-intensity beams such as Cornell's CBETA. [Preview Abstract] |
Friday, October 30, 2020 3:00PM - 3:12PM |
FF.00006: A Mundane Explanation for the ``ATOMKI Anomaly'' Benjamin Sheff, Aleksandrs Aleksejevs, Svetlana Barkanova, Peter Connick, Yury Kolomensky Using the electron-positron pair spectrometer at the 5 MV Van de Graaff-accelerator at the Institute for Nuclear Research, Hungarian Academy of Sciences (ATOMKI), Krasznahorkay {\it et al.} announced data deviating from the Standard Model of particle physics. The authors claim a 6.8 $\sigma$ excess in internal pair creation at high relative angles for the particle pair released in the isoscalar transition $^{8}\mathrm{Be}^*\to ^{8}\mathrm{Be}e^+e^-$ , indicative of a particle of mass circa 16.7 MeV. A similar excess has now been seen in the $^4$He system. A hypothetical gauge boson, a carrier of a fifth force, has been proposed as an explanation for the excesses. We show that a more mundane explanation may lie in the presence of additional nonresonant decay amplitudes, such as a second-order electromagnetic transition. [Preview Abstract] |
Friday, October 30, 2020 3:12PM - 3:24PM |
FF.00007: Particle identification analysis of TREK/E36 Thir Narayan 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 $K_{e2}$ and $K_{\mu2}$, $R_{K} =\Gamma(K_{e2})/\Gamma(K_{\mu2})$, and to search for exotic $K^+$ decay modes accompanied by light neutral bosons, by utilizing a $K^+$ beam stopped in a scintillating fiber target, a combination a highly segmented CsI(Tl) photon calorimeter covering $75\%$ of $4\pi$, charged-particle tracking detectors, and particle identification systems. Since the $R_{K}$ 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. [Preview Abstract] |
Friday, October 30, 2020 3:24PM - 3:36PM |
FF.00008: A survey of quadrupole deformation in nuclei in order to estimate the enhancement of nuclear MQM and its contribution to atomic EDM Prajwal Mohanmurthy, Jeff Winger, Umesh Silwal New sources of CP violation, beyond the known sources in the standard model (SM), are required to explain the baryon asymmetry of the universe. Measurement of a non-zero permanent electric dipole moment (EDM) of fundamental particles, such as in an electron or a neutron, or in nuclei or atoms, can help us gain a handle on the sources of CP violation, both in SM and beyond. Nuclear magnetic quadrupole moment (MQM), the central topic of this work, is CP, P, and T violating. Nucleons and nuclei have a non-zero MQM from sources within the SM. But the nuclear MQM is dramatically enhanced if the nuclei are structurally quadrupole deformed. Multiple sources contribute to an atomic EDM, viz. nuclear EDM, CP violating interactions between the electrons and the nuclei, and finally the nuclear MQM also contributes to the atomic EDM. Unlike nuclear EDM which are shielded by the Schiff effect, nuclear MQMs are not shielded, making the search for them an attractive avenue to probe CP violation. The goal of this work is two fold: (i) to survey the nuclide chart to estimate the enhancement of nuclear MQM in highly quadrupole deformed nuclei, and (ii) to study the relative contribution of these enhanced nuclear MQMs to atomic EDM. [Preview Abstract] |
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