Measurement of R(D) and R(D*) Using Semileptonic Tags and Hadronic τ Decays

We present a measurement of R(D (*) ) = B(B → D (*) τν τ )/B(B → D (*) lν l ) using semileptonic tagging and hadronic τ decays on the 433 fb -1 of data collected at the Υ(4S) resonance using the BaBar detector at the PEP-II collider. We obtain a high statistics data sample using loose selection criteria. The signal is extracted by performing a 2-dimensional fit of the component densities to the kernel density estimate of the data, which is made computationally tractable by algorithmic improvements and speedups provided by graphics processing units. We obtain two distinct central values based on the model used to represent the BB background densities: R(D) = 0.231 ± 0.028 ± 0.028 and R(D * ) = 0.127 ± 0.019 ± 0.031 with a correlation of 0.06 and R(D) = 1.454 ± 0.028 ± 0.028 and R(D * ) = 1.507 ± 0.019 ± 0.031 with a correlation of 0.06. The region encompassed by the two results are consistent with both the Standard Model prediction and the world average.