| This document presents the branching fraction measurement of the decay D+s → tau+nutau, via the decay channel tau + → e+nue nutau, and the extraction of the pseudoscalar decay constant fDs . The measurement is based on 426.9 fb--1 of data collected at the Upsilon(4S) resonance. The branching fraction B ( D+s → tau+nutau) = (4.54+/-0.53+/-0.40+/-0.27)% is measured and fDs is extracted from the branching fraction and determined to be fDs = (233.69+/-13.60+/-10.40+/-7.45) MeV, where the first error is statistical, the second systematic, and the third from the error on branching fractions taken from the world averages of the Particle Data Group. |
