A search for the rare leptonic B decay B- meson decays to tau(-) tau antineutrino recoiling against B+ meson decays to neutral resonant anti D charged lepton, lepton neutrino

This thesis describes a search for the decay B - → tau-nutau in 231.8 x 106 Upsilon(4S) decays recorded with the BABAR detector at the SLAC PEP-II B-Factory. A sample of events with one reconstructed exclusive semi-leptonic B decay (B+ → D¯ *0ℓ+nuℓ) is selected, and in the recoil a search for B- → tau -nutau signal is performed in the following tau decay modes: tau- → e -nuenu tau, tau- → mu-nu munutau, tau- → pi -nutau, tau- → pi-pi 0nutau, and tau- → pi -pi+pi-nutau. We find no evidence of signal, and we set a preliminary upper limit on the branching fraction of B (B- → tau- nutau) < 2.8 x 10-4 at the 90% confidence level (CL). This result is then combined with a statistically independent BABAR search for B- → tau -nutau to give a combined preliminary limit of B (B- → tau- nutau) < 2.6 x 10-4 at 90% CL.