Measurements of BR (b -> tau- nubar_tau X) and BR (b -> tau- nubar_tau D*+- X) and Upper Limits on BR (B- -> tau- nubar_tau) and BR (b -> s nu nubar)

TL;DR

This paper measures inclusive b to tau transitions and sets upper limits on related rare decays, providing tests of the standard model and constraints on new physics parameters like tan(beta)/mH+/- in two-Higgs-doublet models.

Contribution

It presents the first measurements of inclusive b to tau decay branching ratios and sets new upper limits on rare decay modes, constraining physics beyond the standard model.

Findings

Measured b -> tau nu X as (2.43 +/- 0.20 +/- 0.25)%

Measured b -> tau nu D*+/- X as (0.88 +/- 0.31 +/- 0.28)%

Set upper limits on b -> tau nu and b -> s nu nubar decays

Abstract

Inclusive branching ratios involving b to tau transitions are measured in approximately four million hadronic Z decays collected by the ALEPH detector at LEP. The fully-inclusive branching ratio b -> tau nu X and the semi-inclusive branching ratio b -> tau nu D*+/- X are measured to be (2.43 +/- 0.20 +/- 0.25)% and (0.88 +/- 0.31 +/- 0.28)%, in agreement with the standard model predictions. Upper limits on the branching fractions b -> tau nu and b -> s nu nubar are set to 8.3 10**-4 and 6.4 10**-4 at the 90% C.L. These results allow a 90% C.L. lower limit of 0.40 (GeV/c**2)**-1 to be set on the tan(beta)/mH+/- ratio, in the framework of type-II two-Higgs-doublet mode