Search for the Lepton Number Violating Decay Tau to Mu Gamma

Abstract

Using data collected with the BaBar detector between 1999 and 2001, we describe a preliminary search for the neutrinoless decay Tau to Mu Gamma. This data sample includes data collected both on and off the Upsilon(4S) resonance and corresponds to 56 million produced tau pair events. The search has an efficiency of 5.2 +- 0.1(MCstat) +- 0.5(sys) % and an expected background rate of 7.8 +- 1.4 events. We select 13 events in the final sample. As there is no evidence for a signal in this data, we set a preliminary upper limit of B(Tau to Mu Gamma) < 2.0 x 10^-6 @90% CL.