a Measurement of the Inclusive Tau Topological and Exclusive Tau Lepton Going to Muon Neutrino Antineutrino Branching Ratios with Opal at Lep
Abstract
This dissertation describes an analysis of the inclusive tau topological and exclusive tautomununu decay branching fractions completed on a copious sample of tau<=ptons. The data were produced by the Large Electron Positron (LEP) accelerator running at the Z^0 peak and were recorded by the OPAL detector. The final tau decay sample consisted of 3304 tau pair events limited to the barrel region of the detector with a Monte Carlo determined background of only 1.9% attributed mainly to e^+e^ tomu^+mu^ and e^+e^to q{q} events. A total of 899 tautomu nunu decays were identified with an estimated purity of 94%. Correcting for background, identification efficiency, and events preselection bias, a value of B_mu(%) = 16.6 +/ 0.5 +/ 0.4 was obtained. The tau topological branching ratios measured with applied corrections for photon converting tracks are given by B_1 (%) = 85.4 +/ 0.4 +/ 0.4, B_3(%) = 14.2 +/ 0.4 +/ 0.5, and B_5(%) = 0.11 +/ 0.05 +/ 0.11. The current discrepancy related to the fundamental assumption of lepton universality with regard to the tau sector is examined. Expressed as the ratio between the Fermi coupling constants R _{fermi}={G_tauover G_{e,mu}}, the world average values of the tau<=ptonic branching ratios and the tau and mu lifetimes and masses result in R_{fermi} = 0.95 +/ 0.03 where unity is expected for lepton universality. The inclusion of the new value of B _mu resulted in R_{fermi } = 0.90 +/ 0.04 and leaves open the possibility of lepton nonuniversality at the tau sector. A second discrepancy involving the difference between the inclusive and sum of exclusive oneprong tau decay branching fractions is also addressed. Using pre1990 results, the difference between B_sp {1}{inc} and Sigma B_sp{1}{exc} stands at 5.8% +/ 1.4% with the inclusion of theoretical constraints for poorly measured tau decay modes. The new measurements of B_mu and B_1 resulted in Delta B_1(%) = 6.4 +/ 1.6.
 Publication:

Ph.D. Thesis
 Pub Date:
 1992
 Bibcode:
 1992PhDT........25O
 Keywords:

 TAU LEPTON;
 MUON NEUTRINO;
 ANTINEUTRINO;
 Physics: Elementary Particles and High Energy