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 EL: Mini-Symposium: BSM Searches in Fundamental Symmetries II: EDMs |
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Chair: David Kawall, UMass, Amherst Room: Georgian |
Tuesday, October 12, 2021 11:45AM - 11:57AM |
EL.00001: Proton decay amplitudes with physical chirally-symmetric quarks on a lattice. Sergey Syritsyn, Jun-Sik Yoo, Amarjit S Soni, Taku Izubuchi Proton decays are sought as manifestation of baryon number violation predicted by Grand Unification. Their amplitudes depend on nonperturbative QCD, and we calculate them on a lattice with chirally symmetric quarks at the physical point for the first time. Our results largely agree with previous determinations done with heavy quark masses. Therefore, our findings solidify evidence against simple Grand-Unified theories as the absence of observed proton decays cannot be due to chiral QCD dynamics. |
Tuesday, October 12, 2021 11:57AM - 12:09PM |
EL.00002: Search for Invisible Modes of Nucleon Decay with the SNO+ Extended Water Data Morgan Askins Many Grand Unified Theories predict processes that would allow baryons to decay to leptons, violating baryon number conservation and subsequently allowing for both protons and neutrons to decay through non-Standard Model interactions. Distinct from the high energy decay modes that very large water Cherenkov detectors are designed to look for are so-called invisible decays which are only detectable through their subsequent nuclear deexcitations. The SNO+ experiment is uniquely sensitive to this mode of decay due to its low energy threshold, low background radiation, and detector depth. Presented here are updated results which include an additional 190 days of reduced background data. |
Tuesday, October 12, 2021 12:09PM - 12:21PM |
EL.00003: Electric dipole moments of three-nucleon systems in the pionless effective field theory Zichao Yang, Emanuele Mereghetti, Lucas Platter, Matthias R Schindler, Jared Vanasse We calculate the electric dipole moments (EDMs) of three-nucleon systems at leading order in pionless effective field theory. The one-body contributions that arise from permanent proton and neutron EDMs and the two-body contributions that arise from CP-odd nucleon-nucleon interactions are taken into account. Neglecting the Coulomb interaction, we consider the triton and 3He, and also investigate them in the Wigner-SU(4) symmetric limit. We also calculate the electric dipole form factor and numerically find that the momentum dependence of the electric dipole form factor in the Wigner limit is, up to an overall constant (and numerical accuracy), the same as the momentum dependence of the charge form factor. In addition, we include the Coulomb interactions for calculating 3He charge form factors. Finally, we study the cutoff dependence of these observables and find that they are properly renormalized. |
Tuesday, October 12, 2021 12:21PM - 12:33PM |
EL.00004: Strong CP violation: The CP-odd nuclear force and axions sachin shain poruvelil Axions are introduced to reduce the amount of CP violation in strong interactions. In the Standard Model, a small θ¯ term is technically natural but this is no longer true in generic Standard Model extensions. In the framework of the Standard Model Effective Field Theory (SM-EFT), this is reflected by quadratically divergent contributions to θ¯ that signal unsuppressed threshold corrections at the matching scale. The existence then of CP-odd SM-EFT operators necessitates an infrared solution to the strong CP problem, such as a Peccei-Quinn mechanism and the related presence of axions. In the presence of sources of CP violation beyond the QCD θ¯ term, a Peccei-Quinn mechanism leads to CP-violating couplings of axions to Standard Model fields. We investigate the remnant of SM-EFT CP-violating interactions in the form of axion CP-odd couplings and compare the reach of laboratory axion-mediated force experiments and traditional electric dipole moment (EDM) experiments. CP-violating nuclear forces contribute to EDMs in nuclei, diamagnetic atoms, and certain molecules. 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 CP-violating nuclear forces requires a leading-order short-distance operator contributing to 1S0 - 3P0 transitions due to the attractive and singular nature of the strong tensor force in the 3P0 channel. The short-distance operator leads to O(1) corrections to static and oscillating, relevant for axion searches, electric dipole moments. We discuss strategies on how the finite part of the associated low-energy constant can be determined in the case of CP violation from the QCD θ¯ term, by the connection to the charge-symmetry violation in nuclear systems. |
Tuesday, October 12, 2021 12:33PM - 12:45PM |
EL.00005: Bridging the gap between spectroscopy of hot, radioactive ion beams, and cold, precise measurements Adam R Vernon Atomic and molecular ions contained in RF traps are demonstrating to provide some of the most precise measurements possible of electron-nucleon interactions. |
Tuesday, October 12, 2021 12:45PM - 12:57PM |
EL.00006: CP-violating gluon operators and neutron EDM from the instanton vacuum Christian Weiss Experimental studies of hadronic CP-violation rely on theoretical calculations of the hadronic matrix elements of higher-dimensional QCD operators representing the effects of the CP-violating short-distance dynamics at the hadronic scale. We report about a recent calculation of the nucleon matrix element of Weinberg's dimension-6 CP-odd gluon operator fabc (Fdualμν)a (Fμρ)b (Fν ρ)c using the instanton picture of the QCD vacuum [1]. In leading order of the instanton packing fraction, the dimension-6 operator is effectively proportional to the topological charge density (Fdualμν)a (Fμν)a, whose nucleon matrix element is given by the flavor-singlet axial charge and constrained by the U(1)A anomaly. The nucleon matrix element of the dimension-6 operator is obtained substantially larger than in other estimates, because of the strong localization of the nonperturbative gluon fields in the instanton vacuum. We comment on the neutron EDM induced by the dimension-6 gluon operator. We discuss the connection of the CP-violating operators with other operators measuring the gluonic structure of the nucleon, e.g. in deep-inelastic processes. |
Tuesday, October 12, 2021 12:57PM - 1:09PM |
EL.00007: Critical Spin Dressing Magnetic Field Metrology Christopher M Swank The neutron electric dipole moment (nEDM) experiment at the Spallation Neutron Source (SNS) will measure the nEDM via interactions with 3He. Ultimate sensitivity will be reached in that apparatus by using the critical spin dressing technique. Critical spin dressing is the application of an off-resonant oscillatory field that dresses the neutron and 3He spins to have the same effective Larmor precession. Advanced critical spin dressing techniques are in development that can provide high sensitivity measurements of magnetic field gradients with a large dynamic range. Additionally, this measurement technique will distinguish between gradients responsible for limiting the coherence time versus gradients that generate the geometric phase, a linear-in-E frequency shift. A research program has been proposed to develop these techniques at the systematic and operational studies apparatus in the PULSTAR reactor at NCSU. |
Tuesday, October 12, 2021 1:09PM - 1:21PM |
EL.00008: Estimating the impact of magnetic field fluctuations on the critical dressing mode of nEDM@SNS Raymond Tat, Bradley Filippone, Christopher M Swank The neutron electric dipole moment experiment at the Spallation Neutron Source (nEDM@SNS) proposes to measure the nEDM using the spin-dependent capture cross section of neutrons on helium-3. The critical dressing mode of this experiment uses an oscillating magnetic field to dress the gyromagnetic ratios of neutrons and helium-3 to the same value. While this technique grants increased sensitivity to the nEDM by improving the signal-to-noise ratio, this mode of measurement also introduces additional noise from the power supply used to drive the dressing field. This can lead to randomly fluctuating magnetic fields which cause the spins of neutrons and helium-3 to drift apart over time. Here we use second-order time-dependent perturbation theory to compute relaxation and frequency shifts due to power supply noise in terms of the noise power spectrum, and compare these calculations to numerical solutions obtained by integrating the Bloch equations. We then use these results to develop mitigation strategies for this type of noise. |
Tuesday, October 12, 2021 1:21PM - 1:33PM |
EL.00009: 3He polarization and injection system for the nEDM@SNS SOS apparatus Thomas Rao The Systematic and Operations Studies (SOS) for the neutron electric dipole moment (nEDM) experiment at the Spallation Neutron Source (SNS) will measure the trajectory correlation functions of 3He and neutrons in order the determine the expected frequency shift from the geometric phase effect in the nEDM@SNS experiment. To this end the SOS apparatus will utilize Metastability Exchange Optical Pumping (MEOP) to polarize 3He to 80% polarization at room temperature. The 3He will then be injected into the measurement cell inside the cryovessel where the experiment will be performed with concentrations of 3He as low as 10-10 and a temperature of 0.4 K. We will describe the polarization and injection system and report on results from tests of the MEOP system. |
Tuesday, October 12, 2021 1:33PM - 1:45PM |
EL.00010: High Electric Field Studies in Liquid Helium for the nEDM@SNS Experiment Grant Riley The nEDM@SNS collaboration is constructing an experiment to search for a neutron electric dipole moment (EDM) using ultracold neutrons (UCN) stored in superfluid liquid helium. This experiment will be run at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory. The nEDM@SNS experiment requires a very strong and stable electric field in the superfluid helium neutron storage region since the EDM measurement sensitivity depends linearly on field strength. The phenomenon of electric breakdown in liquid helium is poorly understood, which motivates a large R&D effort. An apparatus called the Half Scale High Voltage system (HSHV) has been constructed at Los Alamos National Laboratory to study electrical breakdown in superfluid liquid helium at pressures between the saturated vapor pressure and 1 atm. This experiment will use larger electrodes, up to half the size planned for the nEDM@SNS measurement, complementing results from previous studies. This talk will discuss the engineering and scientific challenges of the HSHV system and show the recent results from the first high voltage studies. |
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