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 LG: Mini-Symposium: Low Energy Probes of New Physics III |
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Chair: Singh Jaideep, MSU |
Saturday, October 31, 2020 10:30AM - 11:06AM |
LG.00001: Toward Measuring the Neutron Electric Dipole Moment Invited Speaker: Christopher Swank The existence of the neutron electric dipole moment (nEDM) is a violation of time reversal (T), and parity (P) symmetries. It is also a violation of Conjugate-Parity (CP) symmetry if CPT is invariant. The Standard Model prediction for the nEDM, which is suppressed to third order loop corrections, is $\approx10^{-32}~\mathrm{e cm}$. The current world experimental limit is 1.3$\times$10$^{-26}$~ecm, from Paul Scherrer Institute. This difference allows a large parameter space for a measurement of new CP violating interactions beyond the Standard Model. The discovery potential is significant, since the Sakharov conditions require a new larger source of CP violation for the observed matter anti-matter asymmetry in the present universe. These CP violating interactions would lead to a larger nEDM than the Standard Model's prediction. There are various approaches to measure the nEDM. The majority of experiments use the Ramsey resonance technique to measure the phase accumulation in the Larmor precession of the neutrons versus applied E-field. Alternatively if polarized $^3$He are introduced with the polarized neutrons then the $^3$He can be used as a neutron phase detector due to their spin dependent reaction. Free precession and spin dressed measurements of the relative phase between the neutron and the $^3$He can be acquired during the duration of the measurement, improving the statistical reach over the Ramsey resonance technique.\\ \\Regardless of the measurement technique, due to the motion of the neutrons through the E-field and imperfections in the B field a systematic frequency shift arises that is proportional to the E-field. The nEDM signal is also proportional the the E field, which is why all nEDM experiments go to great lengths to understand and mitigate this effect. [Preview Abstract] |
Saturday, October 31, 2020 11:06AM - 11:18AM |
LG.00002: Strong CP violation in nuclear physics sachin shain poruvelil Electric dipole moments of nuclei, diamagnetic atoms, and certain molecules are induced by $C\!P$-violating nuclear forces. The naive dimensional analysis predicts these forces to be dominated by long-range one-pion-exchange processes, with short-range forces entering only at next-to-next-to-leading order in the chiral expansion. Based on renormalization arguments we argue that a consistent picture of $C\!P$-violating nuclear forces requires a short-distance operator acting in the unique $j=0$ ${}^1S_0$-${}^3P_0$ transition due to the attractive and singular nature of the strong tensor force in the ${}^3P_0$ channel. We discuss strategies on how the finite part of the associated low-energy constant can be determined in the case of strong $C\!P$ violation from the QCD $\bar \theta$ term, and speculate on the impact on observables of experimental interest such as nuclear EDMs and axion searches. [Preview Abstract] |
Saturday, October 31, 2020 11:18AM - 11:30AM |
LG.00003: Beamline Characterization for the Neutron Electric Dipole Moment Search at Los Alamos National Laboratory Douglas Wong A non-zero neutron electric dipole moment (nEDM) would be evidence of parity (P) and time reversal (T) symmetry breaking. The latter, under the CPT theorem, implies a violation of CP (charge conjugate-parity), which is one of the key Sakharov requirements for baryogenesis to produce the observed baryon asymmetry of the universe. The nEDM search at Los Alamos National Laboratory (LANL) plans to take advantage of a recent neutron source upgrade to realize an incremental improvement on nEDM sensitivity of $3\times10^{-27}e\cdot\text{cm}$. The experimental apparatus is currently being constructed at the Los Alamos Neutron Science Center (LANSCE) with an anticipated data-collection start in 2022. I will describe the result of measurements characterizing the ultra cold neutron (UCN) beamline where the experiment is located. This includes measurements of UCN density in a prototype experimental chamber, UCN transmission through a polarizing magnet, and UCN spin relaxation time. I will also discuss Monte Carlo simulations and additional analysis to understand measurement results. [Preview Abstract] |
Saturday, October 31, 2020 11:30AM - 11:42AM |
LG.00004: Measurement of Neutron Polarization and Transmission for the nEDM@SNS Experiment. Kavish Imam The neutron electric dipole moment experiment at the Spallation Neutron Source (nEDM@SNS) will implement a novel method, which utilizes polarized ultra-cold neutrons (UCN) and polarized $^3$He in a bath of superfluid $^4$He, to place a new limit on the nEDM down to 2-3$\times$10$^{-28}$ e·cm. The experiment will employ a cryogenic magnet and magnetic shielding package to provide the required magnetic field environment to achieve the proposed sensitivity. The polarized cold neutron beam will pass through the cryogenic magnet, therefore, any loss of neutron polarization and transmission through the cryogenic magnet must be characterized. This talk will describe the design and implementation of $^3$He polarimetry setup at the SNS to measure the neutron polarization and transmission losses resulting from passage through the magnetic shielding and cryogenic windows. [Preview Abstract] |
Saturday, October 31, 2020 11:42AM - 11:54AM |
LG.00005: GPU parallelization of spin-tracking simulations for the SNS nEDM experiment Michael Kline, David Mathews, Leah Broussard The neutron's electric dipole moment (nEDM) is measured in the Spallation Neutron Source (SNS) nEDM experiment by detecting the spin-dependent capture events of polarized $^3$He and ultracold neutrons in a measurement cell with parallel magnetic and electric fields. Simulations tracking particles' spin have been performed to better understand the systematic effects present in the experiment. However, spin-tracking on CPUs can be slow and computationally expensive. An additional constraint is maintaining high accuracy for long durations with accumulating rounding errors. GPU parallelization can be used to track many particles simultaneously and improve solver efficiency. We will present an overview of the approach and its advantages and limitations, as well as preliminary results of systematic studies from our simulation to track the spin of particles in the measurement cell. [Preview Abstract] |
Saturday, October 31, 2020 11:54AM - 12:06PM |
LG.00006: Electrodes for a Cryogenic Cavallo Apparatus Marie Blatnik The nEDM@SNS experiment at Oak Ridge National Lab’s Spallation Neutron Source will measure the neutron electric dipole moment with a sensitivity $< 3 \times 10^{-28}$. The measurement cell containing ultracold neutrons will have an electric field of 75 kV/cm produced by a 650 kV electrode. Because the cell must be operated in the few hundred millikelvin range, a traditional 650 kV feedthrough is impractical. Instead, an electrostatic induction machine called a Cavallo Multiplier will multiply a nominal feedthrough voltage into the target high voltage. The Cavallo electrodes were designed based on an empirical hyperbolic tangent envelope, and simulated using COMSOL, a finite element analysis program. The geometric gain, electric field, and spark analysis will be presented. [Preview Abstract] |
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