Download or read book Measurement of the Semileptonic Decays B-]D Tau Nu and B-]D* Tau Nu written by and published by . This book was released on 2009 with total page 29 pages. Available in PDF, EPUB and Kindle. Book excerpt: The authors present measurements of the semileptonic decays B− → D°?− {bar?}{sub?}, B− → D*°?−{bar {nu}}{sub?}, {bar B}° → D?− {bar {nu}}{sub?}, and {bar B}° → D*+?−{bar {nu}}{sub?}, which are sensitive to non-Standard Model amplitudes in certain scenarios. The data sample consists of 232 x 106?(4S) → B{bar B} decays collected with the BABAR detector at the PEP-II e+e− collider. They select events with a D or D* meson and a light lepton (l = e or?) recoiling against a fully reconstructed B meson. They perform a fit to the joint distribution of lepton momentum and missing mass squared to distinguish signal B → D{sup (*)}?− {bar {nu}}{sub?} ({tau}− → l− {bar {nu}}{sub l}{nu}{sub {tau}}) events from the backgrounds, predominantly B → D{sup (*)} l−{bar {nu}}{sub l}. They measure the branching-fraction ratios R(D) {triple_bond}?(B → D{tau}− {bar {nu}}{sub {tau}})/?(B → Dl− {bar {nu}}{sub {ell}}) and R(D*) {triple_bond}?(B → D*{tau}− {bar {nu}}{sub {tau}})/?(B → D* {ell}− {bar {nu}}{sub {ell}}) and, from a combined fit to B− and {bar B}° channels, obtain the results R(D) = (41.6 ± 11.7 ± 5.2)% and R(D*) = (29.7 ± 5.6 ± 1.8)%, where the uncertainties are statistical and systematic. Normalizing to measured B− → D{sup (*)0} {ell}− {bar {nu}}{sub {ell}} branching fractions, they obtain?(B → D{tau}− {bar {nu}}{sub {tau}}) = (0.86 ± 0.24 ± 0.11 ± 0.06)% and?(B → D*{tau}− {bar {nu}}{sub {tau}}) = (1.62 ± 0.31 ± 0.10 ± 0.05)%, where the additional third uncertainty is from the normalization mode. They also present, for the first time, distributions of the lepton momentum,