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Search for rare multi-pion decays of the tau lepton using the babar detector

by Ter-Antonyan, Ruben

Abstract (Summary)
A search for the decay of the tau lepton to rare multi-pion final states is performed using the BABAR detector at the PEP-II asymmetric-energy e+e- collider. The analysis uses 232 fb^{-1} of data at center-of-mass energies on or near the Upsilon(4S) resonance. In the search for the tau->5pi.2pi0.nu decay, we observe 10 events with an expected background of 6.5^{+2.0}_{-1.4} events. In the absence of a signal, we calculate the decay branching ratio upper limit B(tau->5pi.2pi0.nu) < 3.4x10^{-6} at 90% confidence level. This is more than a factor of 30 improvement over the previously established limit. In addition, we search for the exclusive decay mode tau->2omega.pi.nu with the further decay of omega->pi+.pi-.pi0. We observe 1 event, expecting 0.4^{+1.0}_{-0.4} background events, and calculate the upper limit B(tau->2omega.pi.nu) < 5.4x10^{-7} at 90% confidence level. This is the first upper limit for this mode. In the search for the tau->7pi.(pi0).nu decay, we observe 24 events with an expected background of 21.6+/-1.3 events. In the absence of a signal, we calculate the upper limit B(tau->7pi.(pi0).nu) < 3.0x10^{-7} at 90% confidence level. This is an improvement by nearly an order of magnitude over the previously established limit. In addition, we set the first upper limits for the exclusive seven-pion decays B(tau->7pi.nu) < 4.3x10^{-7} and B(tau->7pi.pi0.nu) < 2.5x10^{-7}. We also study the tau->5pi.pi0.nu mode and measure its branching ratio B(tau->5pi.pi0.nu) = (1.79+/-0.04+/-0.14)x10^{-4}, which is consistent with and more precise than the measurements from other experiments.
Bibliographical Information:

Advisor:

School:The Ohio State University

School Location:USA - Ohio

Source Type:Master's Thesis

Keywords:rare tau decays multi pion

ISBN:

Date of Publication:01/01/2006

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