Bulletin of the American Physical Society
APS April Meeting 2020
Volume 65, Number 2
Saturday–Tuesday, April 18–21, 2020; Washington D.C.
Session H11: Mini-Symposium: Tests of Time Reversal Violation IFocus Live
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Sponsoring Units: DNP Chair: Nadia Fomin, University of Tennessee Room: Maryland A |
Sunday, April 19, 2020 10:45AM - 11:21AM Live |
H11.00001: Experimental Searches for Time Reversal Violation Invited Speaker: William Snow Searches for processes which violate CP or T symmetry address important intellectual issues in nuclear/particle/astrophysics and cosmology. CP/T violation is one of the ingredients needed for the explanation of the baryon asymmetry of the universe within the Sakharov paradigm. In this talk we will concentrate on sensitive searches for CP/T violation in systems involving first-generation particles. The discovery of CP/T violation near present levels of sensitivity in such systems would reveal new physics beyond the Standard Model. The null results from existing experiments already probe certain models of baryogengesis at the electroweak scale, where the thermally-activated electroweak sphaleron processes provide the only known source for B-L violation within the Standard Model. [Preview Abstract] |
Sunday, April 19, 2020 11:21AM - 11:33AM Live |
H11.00002: C and CP violation from mirror-symmetry breaking in the $\eta\to\pi^+\pi^-\pi^0$ Dalitz plot Jun Shi, Susan Gardner The CP-violating effects observed thus far appear in flavor-changing processes and in a manner more or less consistent with the predictions of the Standard Model (SM). However, it has long been thought that the observed size of the cosmic baryon asymmetry suggests that mechanisms of CP violation beyond the CKM paradigm should exist. Permanent electric dipole moment searches are exquisite probes of new sources of P and CP violation, whereas processes that would break C and CP are not well studied. The decay $\eta\to\pi^+\pi^-\pi^0$ is an ideal process in which to search for flavor-diagonal C and CP violation. The patterns of C and CP violation that could emerge from an observed violation of mirror symmetry in the Dalitz plot distribution of $\eta\to\pi^+\pi^-\pi^0$ decay would speak to patterns of new physics as well. In particular, the isospin of the underlying C- and CP-violating structures can be reconstructed from their kinematic representation in the Dalitz plot. Our analysis of recent KLOE-2 data reveals that the C- and CP-violating amplitude with total isospin $I = 2$ is much more severely suppressed than that with total isospin $I = 0$. We conclude with a discussion of the constraints on possible new C- and CP-odd operators as derived from SM effective field theory. [Preview Abstract] |
Sunday, April 19, 2020 11:33AM - 11:45AM Live |
H11.00003: A Room Temperature Resonant Axion-like Particle Search Austin Reid, Elijah Guess, Wolfgang Killian, Justin Shortino, W. Michael Snow, Lutz Trahms, Jens Voigt Axions and axion-like particles (ALPs) are CP-odd scalar particles appearing in many extensions of the Standard Model. They generate macroscopic P-odd and T-odd spin-dependent interactions which can be sought in sensitive laboratory experiments. Up to now no direct evidence of cosmological axions has been found. This talk will discuss an experiment that aims to measure fresh, locally sourced axion-like particles by observing precession induced by a periodic monopole-dipole interaction between a rotating mass and a hyperpolarized gas sample. We are developing a room-temperature apparatus with an array of nonmagnetic masses that can spin next to a cell of hyperpolarized $^3$He and $^{129}$Xe applying a calculable periodic potential. As ALPs' known coupling ($g^n_p g^N_s < 4.2\times 10^{-30}$) is assumed to be far weaker than the electromagnetic coupling of the gasses, our sample must be isolated from ambient magnetic field shifts. PTB's BMSR-2 in Berlin has sufficiently low background magnetization that perturbations in the gasses precession frequencies can be read out by a SQUID array. This measurement will establish initial constraints and help probe for new sources of systematic error to benefit ARIADNE, a cryogenic resonant axion search. [Preview Abstract] |
Sunday, April 19, 2020 11:45AM - 11:57AM Not Participating |
H11.00004: NOPTREX: A Neutron Optics Time-Reversal Violation Experiment in Forward-Scattering Neutron-Nucleus Reactions Danielle Schaper One of the motivations to search for new physics Beyond the Standard Model is to understand the baryon asymmetry present in the Universe, namely the glaring discrepancy between the theoretical prediction of the baryon asymmetry based on the Standard Model and the value obtained through observations of the cosmic microwave background. The Neutron OPtics Time Reversal EXperiment (NOPTREX) collaboration is performing R\&D toward an experiment to search for parity-odd (P-odd) and time-odd (T-odd) neutron-nucleus interactions in polarized epithermal ($\sim$1 eV) neutron forward scattering interactions in polarized target nuclei containing $\ell=1$ neutron-nucleus resonances where parity violation is already known to be amplified by several orders of magnitude. NOPTREX can provide a complementary search to other probes of CP violation such as electric dipole moments. This talk will cover the theoretical background $[1]$, current experimental progress, and long-term goals of the NOPTREX collaboration. \\ \\ $[1]$ J. D. Bowman and V. Gudkov, Phys. Rev. C {\bf 90}, 065503 (2014). [Preview Abstract] |
Sunday, April 19, 2020 11:57AM - 12:09PM Not Participating |
H11.00005: Computational analysis of an experimental approach to search for free neutron-antineutron oscillations based on coherent neutron and antineutron supermirror reflection Kylie Dickerson, Mike Snow An observation of neutron-antineutron oscillations ($n$ - $\bar{n}$), which violate both B and B-L conservation, would constitute a scientific discovery of fundamental importance to physics and cosmology. B violation along with CP/T violation and departure from thermal equilibrium are needed to make the baryon asymmetry according to the Sakharov argument. A stringent upper bound on its transition rate would make an important contribution to our understanding of the baryon asymmetry of the Universe by eliminating the postsphaleron baryogenesis scenario in the light quark sector. We extend the work of Nesvizhevsky [Phys. Rev. Lett. 122, 221802 (2019). arXiv: 1810.04988.] and present a quantitative analysis of a means to probe this oscillation time via the use of $n$/$\bar{n}$ supermirrors. Selecting materials with a large contrast in the neutron scattering length density and a continuous distribution of thicknesses minimizes, for sufficiently small transverse momenta of $n$/$\bar{n}$, the relative phase shift of the n and $\bar{n}$ components upon reflection, allowing for sufficient coherence to benefit from the greater phase space acceptance the supermirror provides. [Preview Abstract] |
Sunday, April 19, 2020 12:09PM - 12:21PM On Demand |
H11.00006: TeV-Scale Resonant Leptogenesis from $A_4$ Flavor Symmetry Hachemi Benaoum A new scaling ansatz in the neutrino Dirac mass matrix to explain the low energy neutrino oscillations data, baryon number asymmetry and neutrinoless double beta decay will be presented. A concrete model based on flavor $A_4$ symmetry will be considered to generate such a neutrino Dirac mass matrix and imposes a relation between the two scaling factors. In this model, the right-handed Heavy Majorana neutrino masses are quasi-degenerate at TeV mass scales. Extensive numerical analysis studies have been carried out to constrain the parameter space of the model from the low energy neutrino oscillations data. It is found that the parameter space of the Dirac mass matrix elements lies near or below the MeV. Furthermore, we examine the possibility for simultaneous explanation of both neutrino oscillations data and the observed baryon number asymmetry in the Universe. Such an analysis gives further restrictions on the parameter space of the model, thereby explaining the correct neutrino data as well as the baryon number asymmetry via a resonant leptogenesis scenario. Finally, we show that the allowed space for the effective Majorana neutrino mass is also constrained in order to account for the observed baryon asymmetry. [Preview Abstract] |
Sunday, April 19, 2020 12:21PM - 12:33PM Not Participating |
H11.00007: Search for Time-Reversal Invariance Violation: why complex systems are better? Vladimir Gudkov Searches for electric dipole moments (EDMs) in atomic and molecular systems may provide better sensitivity to Time Reversal Invariance Violating (TRIV) interactions than neutron EDM due to enhancement factors related to complex structure of the system. We consider advantages and disadvantages of many-body nucleon system for the search for TRIV interactions in neutron scattering on heavy nuclei. The absence of final state interactions for the set of specific observables makes these experiments complementary to neutron and atomic electric dipole moment (EDM) measurements. Moreover, in neutron scattering the observables are not a static parameter, as EDM, which leads to an additional enchantment factors for TRIV interactions. Based on these observations we show that neutron scattering experiments at new high flux Spallation Neutron Sources can open new paradigm in the search for TRIV in hadronic interactions and essentially improve the current limits on these TRIV interactions obtained from neutron and atomic EDMs. [Preview Abstract] |
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