Determination of ms and |Vus| from hadronic τ decays

Abstract

The mass of the strange quark is determined from SU(3)-breaking effects in the τ hadronic width. Compared to previous analyses, the contributions from scalar and pseudoscalar spectral functions, which suffer from large perturbative corrections, are replaced by phenomenological parametrisations. This leads to a sizeable reduction of the uncertainties in the strange mass from τ decays. Nevertheless, the resulting ms value is still rather sensitive to the moment of the invariant mass distribution which is used for the determination, as well as the size of the quark-mixing matrix element |Vus|. Imposing the unitarity fit for the CKM matrix, we obtain ms(2 GeV) = 117 ± 17 MeV, whereas for the present Particle Data Group average for |Vus|, we find ms(2 GeV) = 103 ± 17 MeV. On the other hand, using an average of ms from other sources as an input, we are able to calculate the quark-mixing matrix element |Vus|, and we demonstrate that if the present measurement of the hadronic decay of the τ into strange particles is improved by a factor of two, the determination of |Vus| is more precise than the current world average.