Abstract
Tau lepton decays with open strangeness in the final state are measured with the Opal detector at LEP to determine the strange hadronic spectral function of the τ lepton and the mass of the strange quark. The decays τ − → ( K π ) − ν τ , ( K π π ) − ν τ and ( K π π π ) − ν τ with final states consisting of neutral and charged kaons and pions, have been studied. The invariant mass distribution of 93.4% of these final states have been experimentally determined. Monte Carlo simulations have been used for the remaining 6.6% and for the strange final states including η mesons. The reconstructed strange final states, corrected for resolution effects and detection efficiencies, yield the strange spectral function of the τ lepton. The moments of the spectral function which are important input parameters for theoretical analyses, are determined. From the CKM weighted difference of strange and non-strange spectral moments, the mass of the strange quark has been measured to be m s ( m τ 2 ) = ( 84 ± 14 exp ± 6 V us ± 17 theo ) MeV . Furthermore, the branching fractions B ( τ − → K − π 0 ν τ ) = ( 0.471 ± 0.064 stat ± 0.021 sys ) % and B ( τ − → K − π + π − ν τ ) = ( 0.415 ± 0.059 stat ± 0.031 sys ) % have been measured.
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