MC study for the lepton flavor violating tau decay into a lepton and an undetectable particle

Abstract

We search for the charged lepton flavor violating (cLFV) two-body decay, τ→lX using data samples collected with the Belle detector at the KEKB asymmetric-energy e+e− collider, where l is muon or electron and X is a missing particle. One of candidates for an X particle is, for example, a light Z′ boson in the Lμ−Lτ model.This decay mode has been searched for in the ARGUS experiment in 1995. No evidence of the signal has been found and they set upper limits for B(τ→lX)/B(τ→lνν) at several values of X mass. With the Belle data sample, we can perform a much more sensitive search. In this paper we report the estimation of the sensitivities and upper limits of the branching fraction for τ→μX depending on the X mass with a 1 ab−1 data sample.