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 G12: Charged-Lepton Flavor Violation and Other Lepton Physics |
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Sponsoring Units: DPF Chair: Robert Bernstein, Fermilab Room: Marquette III - 2nd Floor |
Sunday, April 16, 2023 10:45AM - 10:57AM |
G12.00001: The expected search sensitivity for μ- → e- at Mu2e in Run I Michael J MacKenzie The standard model (SM) predicts lepton flavor to be a conserved quantity of nature. With the discovery of neutrino oscillations which violate lepton flavor, the SM can be extended to include neutrino mass terms that explicitly violate lepton flavor conservation. These neutrino mass terms lead to charged lepton flavor violation (CLFV) due to loop-level interactions, but the CLFV rates are significantly suppressed by the small neutrino masses to well below an experimentally accessible level (< ∼10-50). New physics models can predict much higher rates of CLFV which are experimentally observable. The observation of a CLFV process would be unambiguous evidence of beyond the SM interactions. |
Sunday, April 16, 2023 10:57AM - 11:09AM |
G12.00002: A data-driven method for antiproton background measurement in Mu2e Namitha Chithirasreemadam, Simone Donati, Pavel Murat, Gianantonio Pezzullo, Alessandro Maria Ricci, Matthew J Stortini, Giulia Nigrelli The Mu2e experiment will search for the CLFV neutrinoless coherent conversion of muon to electron, in the field of an Al nucleus. The experimental signature of the process is a monochromatic conversion electron (CE) with the energy ECE = 104.97 MeV. CE-like electrons could also come from a number of background processes like the cosmic muons, Decay in Orbit (DIO) of muons stopped in the Stopping Target (ST) or antiprotons produced by the proton beam at the Production Target and annihilating in the ST. Our study concerns the antiproton background measurement. The background induced by the antiprotons cannot be efficiently suppressed by the time window cut used to reduce the prompt background because the antiprotons are significantly slower than the other beam particles. We are developing a technique for the in-situ measurement of the antiproton background. ppbar annihilation in the ST is the only source of events in Mu2e with two tracks, simultaneous in time, each with a momentum of ∼100 MeV/c, and we plan to exploit this unique feature. The idea is to identify and reconstruct events with two or more tracks and use them to estimate the background from the ppbar annihilation. As the Mu2e detector is optimized for reconstructing single-track events, we are developing an algorithm to reconstruct multi-track events. The talk presents its status and discusses the prospects of the in-situ estimate of the antiproton background. |
Sunday, April 16, 2023 11:09AM - 11:21AM |
G12.00003: Expected Direct Search Charged Lepton Flavor Violation Sensitivity in μ+ and π+ Decays at Rest Shihua Huang The ability of the Mu2e experiment to probe direct Charged Lepton Flavor Violation (CLFV) μ+ and π+ decay modes is estimated. These direct modes complement the Mu2e indirect search for μ- → e- conversion accomplished using proposed detector validation runs. The μ+ validation run operates at 50% magnetic field and reduced beam intensity, to observe the e+ spectrum from μ+ decay, at and below the Michel edge Ee ≤ 53 MeV. The validation is used to correct systematic errors by mapping the theoretical Michel spectrum, known to Ο(α2), to the observed spectrum. Simultaneously, searches for two-body CLFV μ+ → e+ X decay, where Χ is a light new physics particle can be undertaken. In two weeks of data-taking, Mu2e can achieve 90% C.L. branching ratio limits of ΒR90=10-7 in the mass range 20 ≤ mX ≤ 50 MeV, improving the current experimental limit by two orders of magnitude. In the mass range mX ≤ 20 MeV, if assuming systematic error corrections can be made, it is estimated, using two weeks of data collection, ΒR90(mX=0) = 2.3 × 10-7, an order of magnitude improvement over the current best limit, for the case of V+A or an isotropic coupling. In addition, a two-week π+ validation run measuring the e+ in the decay π+ → e+ ν, at 76% magnetic field and introduction of a momentum degrader, allows searching for π+ → e+ N decay, where N is a spin 1/2 particle, in the mass region 20 ≤ mN ≤ 65 MeV. A branching ratio limit at 90% C.L. of 3 × 10-8 can be achieved, an improvement of the current search sensitivity limit by an order of magnitude. |
Sunday, April 16, 2023 11:21AM - 11:33AM |
G12.00004: Performance of Mu2e Cosmic Ray Veto Detector Modules Yongyi Wu Charged Lepton Flavor Violation (CLFV) processes provide model-independent probes of new physics. The Mu2e experiment at Fermilab will search for the CLFV neutrino-less muon-to-electron conversion in the presence of aluminum nuclei, through the detection of a single monoenergetic electron of 105 MeV energy. The Mu2e experiment aims for a single-event sensitivity of 3×10-17, setting an upper limit for the conversion-to-capture ratio of 8×10-17 at 90% CL. This would improve the current experimental limit by four orders of magnitude. A major experiment background comes from cosmic rays, which can produce electrons indistinguishable from the signature. To reach the desired sensitivity, a cosmic ray veto (CRV) system will be installed to veto the cosmic rays. The plastic-scintillator-based CRV is designed to have a veto efficiency of 99.99%. We report on the CRV's performance using fabricated CRV detector components, confirming that it can reach the designed performance. |
Sunday, April 16, 2023 11:33AM - 11:45AM |
G12.00005: Design and Fabrication of the Cosmic Ray Veto for the Mu2e Experiment Matthew R Solt The Muon-to-Electron Conversion Experiment (Mu2e) at Fermilab will search for the charged-lepton flavor-violating process of a neutrino-less conversion of a muon to electron in the presence of a nucleus. It will do so with an expected sensitivity that improves upon current limits of four orders of magnitude. Such sensitivity will require less than one expected background event over the lifetime of the experiment. The largest background are cosmic rays entering the experimental hall and producing an electron at the expected signal energy. To mitigate this otherwise indistinguishable process, the Mu2e Cosmic Ray Veto (CRV) is designed to veto cosmic rays with 99.99% efficiency while having low dead time in a high intensity environment. The Mu2e CRV is currently being fabricated at the University of Virginia and this talk will discuss the design and fabrication process. |
Sunday, April 16, 2023 11:45AM - 11:57AM |
G12.00006: Flavor-changing light bosons with accidental longevity Kunfeng Lyu We consider a model with a complex scalar field that couples to (e,μ) or (μ,τ) within the ``longevity" window: [|ml1 - ml2|, ml1 + ml2] in which l1 and l2 are the two different charged leptons. Within such a mass window, even a relatively large coupling (e.g. of the size commensurate with the current accuracy/discrepancy in the muon gμ -2 experiment) leads to long lifetimes and macroscopic propagation distance between production and decay points. We propose to exploit several existing neutrino experiments and one future experiment to probe the parameter space of this model. For the μ-e sector, we exploit the muonium decay branching ratio and the production and decay sequence at the LSND experiment, excluding the parametric region suggested by gμ -2 anomaly. For the τ-μ sector, we analyze three main production mechanisms of scalars at beam dump experiments: the Drell-Yan process, the heavy meson decay, and the muon scattering. We explore the constraints from the past CHARM and NuTeV experiments, and evaluate sensitivity for the proposed beam dump experiment, SHiP. The latter can thoroughly probe the parameter space relevant for the gμ -2 anomaly. |
Sunday, April 16, 2023 11:57AM - 12:09PM |
G12.00007: Illustrating Particle Mass Relations by Delta-c Mechanics DT Froedge The purpose of this paper is to illustrate the procedures of Mechanics in calculating relative masses of the internal particles of the nucleus specifically the for this paper the relation between the Proton, Tauon, and the Z boson. |
Sunday, April 16, 2023 12:09PM - 12:21PM |
G12.00008: Optimization of background suppression in the identification of pion decays. Charles J Glaser The pion electronic decay πe2γ branching ratio Rπe/μ = Γ(π→eν(γ)/π→μν(γ) ) provides the best test of electron-muon universality, a standing hypothesis of the Standard Model (SM). |
Sunday, April 16, 2023 12:21PM - 12:33PM |
G12.00009: Properties of electrons in strong magnetic field Samina S Masood We study the properties of electrons in stars which are one of the major source of magnetic field in stars. The behavior of electrons in strong magnetic field is very different from their behavior in free medium. Its basic properties such as its mass and charge are modified in the extreme conditions. These calculations are especially relevant for a system like neutron star where the magnetic field is even stronger than its rest mass in the direction of Lorentz force that is perpendicular to the magnetic field and the direction of linear motion. The impact of these modifications on the behavior of electron in large magnetic field is also discussed. |
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