Background Study for a Search τ→ μγ at Super-c-τ Factory

Abstract

A Monte Carlo study of possible background processes in a search for τ → μγ decay has been performed for conditions of the Super-с–τ factory (at the e + e  center-of-mass energies 3.686 GeV, 3.77 GeV, and 4.17 GeV). The background from e+ e  τ + τ − events has been analyzed. Selection criteria for background suppression have been proposed, and necessary requirements on the detector characteristics have been determined. The search was completed for energy resolution 1.5 % and 2.5 % in the calorimeter. All main tag modes of the tagging tau had taken into account (the total branching ratio all tag modes is about 90 %). The possibility of the longitudinal polarization for initial electron beam was considered for this problem. Measurement of the decay asymmetry became executable in case such polarization in spite of small events statistics. The total sensitivity for branching ratio of the decay τ → μγ at Super-с–τ factory, in case π/μ suppression 1 per 30, is ~ 5 × 10–10. The total number τ + τ − pairs at future Super-B factory about 3 time higher, but the sensitivity for decay τ → μγ at Super–с–τ factory in 5 time better. So the Super-с–τ factory can successfully compete with the Super-B factory in a search for τ→ μγ decay