Measurement of the inclusive b →τνX branching ratio

Abstract Using the L3 detector, the branching ratio BR( b → πν X) has been measured using a sample of Z → b b events tagged by high momentum and high transverse momentum leptons in one hemisphere and with missing energyin the opposite hemisphere. From a sample of 948 000 hadronic events we find BR ( b → πνX ) = (2.4 ± 0.7 (stat.) ± 0.8 (syst.))%.