Measurement of the Strangeness Spectral Function and the Mass of the Strange Quark with the Opal Detector at LEP

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.