Combined analysis of semileptonic B decays to D and D*: R(D(*)), |Vcb|, and new physics

The measured (B) over bar -> D-(*()) l (nu) over bar decay rates for light leptons (l = e, mu) constrain all (B) over bar -> D-(*()) semileptonic form factors, by including both the leading and O(Lambda(QCD)/m(c,b)) subleading Isgur-Wise functions in the heavy quark effective theory. We perform a novel combined fit to the (B) over bar -> D-(*()) l (nu) over bar decay distributions to predict the (B) over bar -> D-(*()) tau(nu) over bar rates and determine the Cabibbo-Kobayashi-Maskawa matrix element vertical bar V-cb vertical bar. Most theoretical and experimental papers have neglected uncertainties in the predictions for form factor ratios at order Lambda(QCD)/m(c,b), which we include. We also calculate O(Lambda(QCD)/m(c,b)) and O(alpha(s)) contributions to semileptonic (B) over bar -> D-(*()) l (nu) over bar decays for all possible b -> c currents. This result has not been available for the tensor current form factors, and for two of those, which are O(Lambda(QCD)/m(c,b)), the corrections are of the same order as approximations used in the literature. These results allow us to determine with improved precision how new physics may affect the (B) over bar -> D-(*()) tau(nu) over bar rates. Our predictions can be systematically improved with more data; they need not rely on lattice QCD results, although these can be incorporated.