Bulletin of the American Physical Society
APS April Meeting 2023
Volume 68, Number 6
Minneapolis, Minnesota (Apr 15-18)
Virtual (Apr 24-26); Time Zone: Central Time
Session C16: Mini-Symposium: Lepton Number Violation IMini-Symposium
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Sponsoring Units: DNP DPF Chair: Ian Guinn, University of North Carolina at Chapel Hill Room: Marquette VII - 2nd Floor |
Saturday, April 15, 2023 1:30PM - 2:06PM |
C16.00001: Lepton Number Violation Invited Speaker: Kaladi S Babu TBD |
Saturday, April 15, 2023 2:06PM - 2:18PM |
C16.00002: TPC Track Visualization Using a Camera Readout for Neutrinoless Double Beta Decay Nicholas Byrnes One of the greatest unanswered questions in our universe is the generation mechanism for matter-antimatter asymmetry. One solution is that the neutrino is a Majorana particle, or that it is its own antiparticle. The best way to observe this would be the direct observation of neutrinoless double beta decay, a process in which an isotope undergoes simultaneous beta decays without the emission the electron antineutrinos. The Neutrino Experiment with a Xenon TPC (NEXT) is an electroluminescence (EL) TPC searching for this decay, using gaseous 136Xe as both the decay and detection medium. The main difficulty in observing this decay is the half-life; in 136Xe, the leading limit is 1.07e26 years, set by KamLAND-Zen. This decay rarity, coupled with radiogenic and cosmogenic backgrounds, necessitates development of new techniques to maximize search potential. One technique under investigation by NEXT is a topological readout using an external camera setup. This removes the SiPM readouts from the detector interior and the need for wavelength shifting chemicals, eliminating a substantial source of radioactive background and improving track resolution. This presentation shows, for the first time, the direct observation of alpha, beta, and muon EL tracks using a VUV image intensifier coupled to a high QE camera. This is the first in a series of demonstrators being built at the University of Texas Arlington and Argonne National Lab. |
Saturday, April 15, 2023 2:18PM - 2:30PM |
C16.00003: Tri-nucleon decay in 130Te with CUORE Vivek Sharma The conservation of baryon number in the Standard Model originates from an empirical symmetry and does not derive from first principles. Any discovery of a phenomenon that indicates that this symmetry is broken would have far-reaching consequences for our understanding of the universe, in particular the origin of the matter-antimatter asymmetry. A proposed process that can violate baryon number is the tri-nucleon decay, which involves three nucleons in a nucleus decaying simultaneously. The products of this decay are emitted with GeV-scale energy, which can serve as an excellent signal in CUORE. In cases where the resulting daughter nucleus is unstable, the subsequent decay radiation can be an additional signature that can be utilized for a coincidence analysis. We will present the details on the search signatures, the associated backgrounds and the analysis techniques employed. |
Saturday, April 15, 2023 2:30PM - 2:42PM |
C16.00004: Leptogenesis from Lepton-Number-Breaking Scalars Brian Shuve, Matthew S Fox, Carlos Tamarit, Lucien Mallett Leptogenesis via right-handed neutrino (RHN) decay is a well-motivated model of baryogenesis that arises naturally in models accommodating Standard Model neutrino masses. The origin of the RHN masses is unknown, but if their masses arise dynamically the resulting lepton asymmetry can be suppressed due to the additional RHN interactions present. In this work, we show that in such scenarios there exists a previously unconsidered source of lepton asymmetry from the decays of the Higgs boson responsible for spontaneously breaking lepton number. This new source can greatly exceed the contribution to the asymmetry from to the decay of RHNs themselves, and render leptogenesis viable for parameters that otherwise wouldn't work in the minimal scenario. We present analytic and numerical studies of the asymmetry due to lepton-number-breaking scalar decay, along with cosmological and theoretical considerations for when this new source could be relevant for leptogenesis. |
Saturday, April 15, 2023 2:42PM - 2:54PM |
C16.00005: A Search for Lorentz and CPT Violations in Double-β Decay with the Full EXO-200 Dataset Jonathan M Echevers Neutrinoless double beta (0νββ) decay is currently one of the most compelling searches in nuclear and particle physics. If found, it would imply the existence of Majorana fermions and lepton number violation, both new physics beyond the Standard Model. The EXO-200 experiment consisted of a time projection chamber (TPC) with 200 kg of enriched liquid xenon (LXe) optimized to search for 0νββ of 136Xe. Data acquisition took place from 2011 to the end of 2018, with a total exposure of 234.1kg·yr. We found no statistically significant evidence for 0νββ, leading to a lower limit on the half-life of 3.5×1025 yr at the 90% confidence level. The ultra-low background necessary for this search also provides a unique opportunity to probe other exotic processes, such as Lorentz and CPT violation, predicted by the Standard Model Extension (SME). This presents itself in double beta decay as a spectral perturbation due to neutrino coupling with an SME Lorentz-violating tensor field. A first search for this process with EXO-200 was published in 2016 using a subset of the dataset. In this talk, we will present the analysis and status of an updated search using the full EXO-200 dataset with an optimized analysis strategy and improved systematic uncertainties. |
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