Thesis BELLE2-MTHESIS-2023-036

Analysis on the Lepton Flavor Violating Decay τ -> μ π0 in Belle II

Marton Nemeth-Csoka ; Christian Kiesling

Ludwig-Maximilians-University Munich

Abstract: This work focuses on the lepton flavor violating decay τ → μπ0 with the goal to explore the prospects of finding New Physics in this particular channel. Belle and BaBar found the upper limit for the branching ratio of this decay to be 􀀀(τ → μπ0)/􀀀tot < 2.7 · 10−8 while having an available luminosity of Lint = 901 fb−1. In the analysis, the decay simulated by a Monte Carlo software including detectors and full reconstruction to get an understanding of the overall kinematics. The signal is reconstructed directly by combining possible pairs of μ and π0, where the π0 is reconstructed from two photons. Based solely on kinematics the detector is able to reconstruct 64% of the simulated signal. When studying the background, the largest background is that of the pair production of muons, together with light quarks and τ that decay according to the predictions of the SM. After applying kinematic cuts and requiring a moderate confidence threshold for the identification of the muon, only 5.3% of the signal is left, but the background is fully suppressed in a sample equaling 100 fb−1. Belle claimed a signal sensitivity of 4.2% with a background prediction of 0.64 events, BaBar claimed 4.8% and predicted 1.33 events, the former with a recorded luminosity nine times larger, and the latter four times larger than this sample. This suggests, that Belle II with its anticipated 50 ab−1 luminosity will be able to completely dominate the other two experiments. To further confirm this, the next step would be to conduct studies with larger MC datasets, before moving on to actual data, which may comprise more than Lint = 500 fb−1 by the end of 2022.

Note: Presented on 27 11 2021
Note: MSc

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 Record created 2023-07-19, last modified 2023-07-21

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