Measuring R(d(∗) ) For B(b → D(∗) τντ ) Using Semileptonic Tags and τ Decays to Hadrons

Abstract

We perform a measurement of R(D(^∗) ) for B → D(^∗) τντ using semileptonic tagging and τ decays to hadrons on the 429 fb⁻¹ of data that BABAR collected at the Υ(4S) resonance. This is the first measurement of R(D(^∗) ) using the specified reconstruction channels. Candidate selection was performed with supervised learning, where the training labels were obtained by solving an instance of subgraph isomorphism. The signal extraction was performed by solving an optimization problem whose objective function required the evaluation of kernel density estimates that were accelerated by a branch-and-bound algorithm as well as with a GPU. The training data for the density estimates were themselves the output of two classifier scores. We present a 68% and 95% confidence regions of R(D(^∗) ), which do not show enough evidence to reject the standard model prediction.