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

by 1977- Ter-Antonyan, Ruben

Abstract (Summary)
A search for the decay of the ? 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 ?(4S) resonance. In the search for the ? ? ? 3??2?+2?0?? 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(? ? ? 3??2?+2?0??) < 3.4 × 10?6 at the 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 ? ? ? 2????? with the further decay of ? ? ???+?0. We observe 1 event, expecting 0.4+1.0 ?0.4 background events, and calculate the upper limit B(? ? ? 2?????) < 5.4 × 10?7 at the 90 % confidence level. This is the first upper limit for this mode. In the search for the ? ? ? 4??3?+(?0)?? 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(? ? ? 4??3?+(?0)??) < 3.0 × 10?7 at the 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(? ? ? 4??3?+?? ) < 4.3 × 10?7 and B(? ? ? 4??3?+?0??) < 2.5 × 10?7. ii We also study the ? ? ? 3??2?+?0?? mode and measure its branching ratio B(? ? ? 3??2?+?0?? ) = (1.79 ± 0.04 ± 0.14) × 10?4, which is consistent with and more precise than the measurements from other experiments. iii
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School:The Ohio State University

School Location:USA - Ohio

Source Type:Master's Thesis

Keywords:leptons nuclear physics pions

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