Experimental review of τ lepton studies at the B factories

Denis Epifanov,A Denig,C.-F Redmer

doi:10.1051/epjconf/201921805001

Denis Epifanov, A Denig + Show 1 more

Open Access

https://doi.org/10.1051/epjconf/201921805001

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Abstract

Recent results of a high-statistics τ lepton studies at B factories are reported. Reviewed are the measurements of Michel parameters in leptonic and radiative leptonic τ decays at Belle, as well as the measurement of the branching fractions of the radiative leptonic τ decays at BABAR. Searches for CP symmetry violation in hadronic decays with $ \mathop K\nolimits_S^0 $ are also briefly discussed.

Highlights

The world largest data set of τ leptons collected at e+e− B factories [1] opens new era in the precision tests of the Standard Model (SM)
While Belle focused on the measurement of Michel parameters in these decays [7, 8], BABAR performed precision tests of the lepton universality [9] and measurement of the branching fractions [10]
In the low-energy four-fermion framework, the matrix element of leptonic τ decay can be written in the generalized form with ten possible Lorentz structures, which are characterized by ten complex coupling constants giNj, i, j = L, R; N = S, V, T

Summary

Introduction

The world largest data set of τ leptons collected at e+e− B factories [1] opens new era in the precision tests of the Standard Model (SM). In the SM, τ decays due to the charged weak interaction described by the exchange of W± with a pure vector coupling to only left-handed chirality fermions. Leptonic decays are the only ones in which the electroweak couplings can be probed without disturbance from the strong interactions. This makes them an ideal system to study the Lorentz structure of the charged weak current. While Belle focused on the measurement of Michel parameters in these decays [7, 8], BABAR performed precision tests of the lepton universality [9] and measurement of the branching fractions [10]. Of particular interest are strangeness changing Cabibbo-suppressed hadronic τ decays, in which large CP symmetry violation (CPV) could appear from a charged scalar boson exchange [12]

Ordinary leptonic τ decays

Radiative leptonic τ decays

Study of radiative leptonic τ decays at BABAR

Findings

CPV in τ decays with KS0