HEAVY-QUARK EXPANSION FOR THE INCLUSIVE DECAY (B)OVER-BAR-]TAU(NU-OVER-BARX

We calculate the differential decay rate for inclusive B --> taunuXBAR transitions to order 1/m(b)2 in the heavy quark expansion, for both p olarized and unpolarized tau leptons. We show that using a systematic 1/m(b) expansion significantly reduces the theoretical uncertainties i n the calculation. We obtain for the total branching ratio BR(BBAR --> taunuXBAR) = 2.30 +/- 0.25%, and for the tau polarization A(pol) = -0 .706 +/- 0.006. From the experimental measurement of the branching rat io at LEP, we derive the upper bound lambda1 less-than-or-equal-to 0.8 GeV2 for one of the parameters of the heavy quark effective theory.