Search for the lepton flavour violating decay τ − → μ − μ + μ −

Abstract

No evidence is found for a signal, and a limit is set at 90% confidence level on the branching fraction, B(τ − → µ − µ + µ − ) < 4.6 × 10 −8 .

Lepton Flavour Violation in Tau Decays: Results and Prospects at the LHC

“…A combined fit is performed to the three-muon invariant mass distribution of the most sensitive bins in M 3body × M PID . The result is consistent with the background-only hypothesis, and an upper limit [2] (4) is set on the branching fraction using the CLs method [9,10]. This limit is a factor 2.5 higher than the current best limit [11], set by the Belle experiment.…”

“…An upper limit [1] (2) is set on the τ − → μ − μ + μ − branching fraction using the CLs method [9,10]. Although this limit is not yet competitive with the results from the LHCb [2] and Belle [11] experiments, it demonstrates ATLAS' potential for performing competitive LFV searches using the LHC run 2 data and beyond, and its capabilities to reconstruct and trigger on low-p T muons.…”

“…This report presents three searches for LFV decays at the LHC: A search for τ − → μ − μ + μ − , performed by the ATLAS [1] and LHCb [2] experiments, for Z 0 → τ ± μ ∓ , performed by ATLAS [3], and for D 0 → e ± μ ∓ , performed by LHCb [4]. The ATLAS searches use protonproton collision data corresponding to an integrated luminosity of 20.3 fb −1 collected by the ATLAS detector in 2012 at a centre-of-mass energy of 8 TeV.…”

First observation of the rareB+→D+K+π−decay

“…Similar fitting techniques have been used successfully in several previous LHCb analyses [22][23][24][25]. A loose requirement is placed on the output of NN2 and the remaining data in each sample are divided into six bins of the NN2 output variable, each containing a similar number of signal decays.…”

LHCb long term plans beyond the current upgrade

“…The luminosity accumulated at the B-factories was three orders of magnitude bigger than what LHCb accumulated in RUN-I, and the analysis efficiency and background levels at LHCb are worse compensating for the much larger production rate. Nonetheless, LHCb has produced limits [9] with RUN-I data (∼ 10 11 τ) on the process τ ± → µ + µ − µ ± very close to the ones obtained by BaBar and Belle (∼ 10 9 τ) [10], resulting in a world average of B(τ ± → µ + µ − µ ± ) < 1.2 × 10 −8 at 90% C.L. LHCb expects to improve on the B-factories results by the end of RUN-2.…”