%0 Generic
%A Adametz, Aleksandra
%D 2011
%F heidok:12325
%K CKM-matrix , tau , lepton , branching fraction , BABAR-Detector
%R 10.11588/heidok.00012325
%T Measurement of tau decays into a charged hadron accompanied by neutral pi-mesons and determination of the CKM matrix element |V_us|
%U https://archiv.ub.uni-heidelberg.de/volltextserver/12325/
%X This thesis presents the branching fraction measurement of the tau^-->K^- npi^0 nu_tau (n = 0,1,2,3) and tau^-->pi^- npi^0 nu_tau (n = 3,4) decays. The measurement is based on a data sample of 435 million tau pairs produced in e^+e^- collisions and collected with the Babar detector in  1999-2008. The analysis is validated using precisely known tau decays as control modes. The measured branching fractions are BR( tau^-->K^-nu_tau) =  (7.100 +- 0.033 +- 0.156) x 10^{-3}, BR( tau^-->K^- pi^0 nu_tau) =(5.000 +- 0.020 +- 0.139) x 10^{-3}, BR( tau^-->K^- 2pi^0 nu_tau) = (5.654 +- 0.144 +- 0.323) x 10^{-4}, BR( tau^-->K^- 3pi^0 nu_tau) = (1.642 +- 0.279 +- 0.375) x 10^{-4}, BR(tau^-->pi^- 3pi^0 nu_tau) = (1.216 +- 0.010 +- 0.047) x 10^{-2}, BR(tau^-->pi^- 4pi^0 nu_tau) =  (1.041 +- 0.067 +- 0.090) x 10^{-3},  where the first uncertainty is statistical and the second systematic. The branching fraction BR(tau^-->pi^- 4pi^0 nu_tau) is measured for the first time. The precision of the results is comparable or significantly improved with respect to previous measurements.  The branching fraction BR(tau^-->K^- nu_tau) is combined with a lattice QCD calculation of the kaon decay constant to obtain the Cabibbo-Kobayashi-Maskawa matrix element |V_us| = 0.2224 +- 0.0025(exp) +- 0.0029(theo). The branching fractions of the tau decays into a kaon are combined with the current world averages. The resulting averages are used in the determination of the total tau branching fraction, BR_{strange}, into strangeness |S| = 1 final states. BR_{strange} is used in conjunction with |V_ud| and a small SU(3)-symmetry breaking correction to compute |V_us| = 0.2176 +- 0.0025(exp) +- 0.0010(theo).