A search for lepton-flavour violating τ→ 3μ decays with the ATLAS detector

2026/03/31 by ATLAS Collaboration
Physics and Astronomy · #hep-ex

paper · pdf · doi:10.1016/j.physletb.2026.140748

published as Phys. Lett. B 880 (2026) 140748 · 37 pages in total, author list starting page 20, 4 figures, 3 tables, published to Phys. Lett. B 880 (2026) 140748. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/BPHY-2018-05

arxiv created 2026/08/05 · arxiv updated 2026/08/06

Abstract

A search for charged lepton flavour violation in τ→ 3μ decays is performed in pp collisions at a centre-of-mass energy of 13 TeV using ATLAS data collected between 2016 and 2018, corresponding to an integrated luminosity of 137 fb^-1. The search is optimised for the electroweak W → τν production channel, due to its higher trigger efficiency, but also considers potential signal events from heavy-flavour production. Data are collected using two-muon and three-muon triggers and a multivariate analysis is used to separate the signal from the background. An unbinned likelihood fit is then performed to the resulting three-muon invariant mass spectrum and the data are found to be compatible with the background-only hypothesis. The observed (expected) limit on the branching ratio B(τ→3μ) is found to be 8.7× 10^-8 (7.5× 10^-8) at 90% CL.

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