Bulletin of the American Physical Society
2017 Fall Meeting of the APS Division of Nuclear Physics
Volume 62, Number 11
Wednesday–Saturday, October 25–28, 2017; Pittsburgh, Pennsylvania
Session DG: Mini-Symposium on Electro-weak Physics and Fundamental Symmetries II |
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Chair: Ciprian Gal, University of Virginia Room: Marquis A |
Thursday, October 26, 2017 10:30AM - 10:42AM |
DG.00001: The Search for Fundamental Symmetry Violation in Radium Nuclei Matthew Dietrich, Michael Bishof, Kevin Bailey, John Greene, Peter Mueller, Thomas O'Connor, Zheng-Tian Lu, Tenzin Rabga, Roy Ready, Jaideep Singh Electric dipole moments (EDMs) are signatures of time-reversal, parity, and charge-parity (CP) violation, which makes them a sensitive probe of expected new physics beyond the Standard Model. Due to its large nuclear octupole deformation and high atomic mass, the radioactive Ra-225 isotope is a favorable EDM case; it is particularly sensitive to CP-violating interactions in the nuclear medium. We have developed a cold-atom approach of measuring the atomic EDM of atoms held stationary in an optical dipole trap, which we have used to place the only upper limit on the EDM of radium, \textbar d(225Ra)\textbar \textless 1.4e-23 e-cm. This is not only the first time laser-cooled atoms have been used to measure an EDM, but also the first time the EDM of any octupole deformed species has been measured. We will present results on a new approach to spin detection that we expect to improve our EDM sensitivity by a factor of 20. Combined with upcoming improvements to our electric field generation, the next measurement should be competitive with the best neutron EDM result, in terms of sensitivity to CP-violating interactions. This work is supported by the U.S. DOE, Office of Science, Office of Nuclear Physics, under contract DE-AC02-06CH11357. [Preview Abstract] |
Thursday, October 26, 2017 10:42AM - 10:54AM |
DG.00002: Nuclear Matrix Elements for Tests of Local Lorentz Invariance Violation Alex Brown, George Bertsch, Luis Robledo The nuclear matrix elements for the momentum quadrupole operator are important for the interpretation of precision atomic physics experiments that search for violations of Lorentz and CPT symmetry. We use the configuration-interaction nuclear shell model and self-consistent mean field theory to calculate these matrix elements for $^{21}$Ne, $^{131}$Xe, $^{173}$Yb and $^{201}$Hg. We show that these matrix elements are strongly suppressed by the many-body correlations, in contrast to the well known enhancement of the spatial quadrupole moments. [Preview Abstract] |
Thursday, October 26, 2017 10:54AM - 11:06AM |
DG.00003: Update on PEN: A Precision Measurement of the $\pi\rightarrow$e$\nu(\gamma)$ Branching Ratio Charles Glaser The PEN collaboration performed a precision measurement of the $\pi^+\rightarrow e^+\nu_e(\gamma)$ branching ratio at the Paul Scherrer Institute with the goal of obtaining a relative uncertainty of $5\times10^{-4}$ or better. Measurement of the branching ratio $\Gamma(\pi\rightarrow e\bar{\nu}(\gamma))/\Gamma(\pi\rightarrow \mu \bar{\nu}(\gamma))$ provides the most sensitive test of lepton universality. Deviations from Standard Model predictions would signify ``new'' or non V$-$A interactions, physics not currently in the Standard Model. The PEN detector consists of active target and beam counters, a mini time projection chamber, two cylindrical multi-wire proportional chambers, a plastic scintillating hodoscope, and a spherical 240-module pure CsI electromagnetic calorimeter. Discrimination between the main background and signal is facilitated by using predicted timings and energies from multiple detector elements. Proper accounting for decays in flight, detector efficiencies, and detector response, specifically the low energy tail response of the CsI calorimeter, is required for branching ratio extraction. We will update the status of the PEN project. [Preview Abstract] |
Thursday, October 26, 2017 11:06AM - 11:18AM |
DG.00004: Information entropy exchange between a particle and an observer and the arrow of time Athansios Petridis, Daniel Deeter The quantum mechanical transition amplitude for a free particle is calculated using the path integral formalism. This amplitude is the kernel of the Schrödinger equation. A Wick rotation of the time increment transforms the kernel into a partition function that depends on the space and time intervals of the transition, with the temperature being the inverse of the time increment. The information entropy exchange between the system and the observer during the transition is calculated from the partition function. The requirement that this be real-valued leads to uncertainty-type relations. Furthermore, the transition exhibits positive information entropy exchange for small time intervals. Coordinate-time reversal maintains the sign of the information entropy exchange, therefore, producing an arrow of time. The related statistical weight is inversely proportional to the square root of the time interval and can be interpreted based on simple statistical rules. In the way the fundamental equations of quantum mechanics can be derived from a postulate on information entropy exchange. [Preview Abstract] |
Thursday, October 26, 2017 11:18AM - 11:30AM |
DG.00005: Prospects for Searching for Time-Reversal Violation In Pa-229 Jaideep Singh Certain pear-shaped nuclei are expected to have enhanced sensitivity to time-reversal and parity-violating interactions originating within the nuclear medium. In particular, Pa-229 is thought to be about 100,000 times more sensitive than Hg-199 which currently sets some of the most stringent limits for these types of interactions. Several challenges would first have to be addressed in order to take advantage of this discovery potential. First, there is not currently a significant source of Pa-229; however, there are plans to harvest Pa-229 from the FRIB beam dump. Second, the spin-5/2 nucleus of Pa-229 limits its coherence time while also making it sensitive to systematic effects related to local field gradients. On the other hand, this also gives Pa-229 an additional source of signal in the form of a magnetic quadrupole moment (MQM) which violates the same symmetries as an EDM but is not observable in spin-1/2 systems. Third, in order to compensate for the small atom numbers and short coherence times, the Pa-229 atoms would have to be probed with exceptionally large electric & magnetic fields that are only possible if Pa-229 is a part of a polar molecule or embedded inside of an optical crystal. I will present an our plans to test some of these concepts using stable Pr-141. [Preview Abstract] |
Thursday, October 26, 2017 11:30AM - 11:42AM |
DG.00006: A Current-Mode Detector for Use in NOPTREX Time Reversal Experiment Danielle Schaper Searches for new sources of time reversal (T) violation are one of the highest intellectual priorities in nuclear, particle, and astrophysics. The Neutron Optics Time Reversal Experiment (NOPTREX) Collaboration aims to conduct a sensitive null-test search for T-violation in polarized neutron transmission through a polarized nuclear target which possesses low-energy p-wave resonances. We are developing a low-noise current-mode neutron detector with near-unit efficiency and fast time response to resolve the resonance shapes. This talk will discuss the design of the detector as well as test measurements taken on indium and tantalum resonances at the NOBORU test beam at the Japan Proton Accelerator Complex (J-PARC) in June 2017 using a set of prototypical detectors, analog electronics, and data acquisition module. We will also briefly discuss plans for an experiment at LANSCE to measure the P-odd asymmetry in the 0.734 eV p-wave resonance in $^{139}$La to 1% accuracy. [Preview Abstract] |
Thursday, October 26, 2017 11:42AM - 11:54AM |
DG.00007: Searching for Dark Photons with the SeaQuest Spectrometer Sho Uemura The existence of a dark sector, containing families of particles that do not couple directly to the Standard Model, is motivated as a possible model for dark matter. A ``dark photon'' -- a massive vector boson that couples weakly to electric charge -- is a common component of dark sector models. The SeaQuest spectrometer at Fermilab is designed to detect dimuon pairs produced by the interaction of a 120 GeV proton beam with a rotating set of thin fixed targets. An iron-filled magnet downstream of the target, 5 meters in length, serves as a beam dump. The SeaQuest spectrometer is sensitive to dark photons that are mostly produced in the beam dump and decay to dimuons, and a SeaQuest search for dark sector particles was approved as Fermilab experiment E1067. As part of E1067, a displaced-vertex trigger was built, installed and commissioned this year. This trigger uses two planes of extruded scintillators to identify dimuons originating far downstream of the target, and is sensitive to dark photons that travel deep inside the beam dump before decaying to dimuons. This trigger will be used to take data parasitically with the primary SeaQuest physics program. In this talk I will present the displaced-vertex trigger and its performance, and projected sensitivity from future running. [Preview Abstract] |
Thursday, October 26, 2017 11:54AM - 12:06PM |
DG.00008: The MOLLER Experiment: "An Ultra-precise Measurement of the Weak Charge of the Electron using moller Scattering" Rakitha Beminiwattha Parity Violating Electron Scattering (PVES) is an extremely successful precision frontier tool that has been used for testing the Standard Model (SM) and understanding nucleon structure. Several generations of highly successful PVES programs at SLAC, MIT-Bates, MAMI-Mainz, and Jefferson Lab have contributed to the understanding of nucleon structure and testing the SM. But missing phenomena like matter-antimatter asymmetry, neutrino flavor oscillations, and dark matter and energy suggest that the SM is only a “low energy” effective theory. The MOLLER experiment at Jefferson Lab will measure the weak charge of the electron, $\rm Q^e_W = 1 - 4 sin^2\theta_W$ , with a precision of $\rm 2.4\%$ by measuring the parity violating asymmetry in electron-electron (\moller) scattering and will be sensitive to subtle but measurable deviations from precisely calculable predictions from the SM. The MOLLER experiment will provide the best contact interaction search for leptons at low OR high energy makes it a probe of physics beyond the Standard Model with sensitivities to mass-scales of new PV physics up to 7.5 TeV. Overview of the experiment and recent pre-R&D progress will be reported. [Preview Abstract] |
Thursday, October 26, 2017 12:06PM - 12:18PM |
DG.00009: Precise Measurement of $\Gamma(K^+\rightarrow e^+\nu)/\Gamma(K^+\rightarrow \mu^+\nu)$ and Search for New Physics by the TREK-E36 Experiment Tongtong Cao The J-PARC TREK-E36 experiment will provide a precise measurement of the ratio of decay widths $R_K=\Gamma(K^+\rightarrow e^+\nu)/\Gamma(K^+\rightarrow \mu^+\nu)$ to test lepton universality. $R_K$ is very precisely predicted by the Standard Model (SM) with the uncertainty of $4\times10^{-4}$ and a deviation from the prediction would very clearly indicate the existence of New Physics beyond the SM. Additionally, the experiment intends to search for visible decay modes of $A^{'}\rightarrow e^+e^-$ in $K^+$ decays. The existence of an $A^{'}$ is well motivated by dark matter observations and $g_{\mu}$-2 anomaly, as well as the proton radius puzzle. In the E36 experiment, a $K^+$ beam was stopped by a scintillating fiber target, and charged decay products were momentum analyzed and tracked by a 12-sector superconducting toroidal magnet spectrometer and multi-wire proportional chambers combined with a photon calorimeter with a large solid angle (75\% of $4\pi$) and 3 different particle identification systems. In this talk, the status of the data analysis is presented. This work has been supported by the U.S. DOE Award DE-SC0013941. [Preview Abstract] |
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