Search for the Decay tau- --> 3pi- 2pi+ 2pi0 nu_tau

TL;DR

This paper reports a search for specific tau lepton decay modes using BABAR data, setting new upper limits on their branching ratios, with no significant signal observed.

Contribution

The study provides the first upper limit for the tau- --> 2omega pi- nu_tau decay and improves the limit for tau- --> 3pi- 2pi+ 2pi0 nu_tau.

Findings

No significant signal observed for the decay modes.

Upper limit for tau- --> 3pi- 2pi+ 2pi0 nu_tau is 3.4x10^{-6}.

Upper limit for tau- --> 2omega pi- nu_tau is 5.4x10^{-7}.

Abstract

A search for the decay of the tau lepton to five charged and two neutral pions is performed using data collected by 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 Y(4S) resonance. We observe 10 events with an expected background of 6.5^{+2.0}_{-1.4} events. In the absence of a signal, we set the limit on the branching ratio B(tau- --> 3pi- 2pi+ 2pi0 nu_tau) < 3.4x10^{-6} at the 90% confidence level. This is a significant improvement over the previously established limit. In addition, we search for the decay mode tau- --> 2omega pi- nu_tau. We observe 1 event with an expected background of 0.4^{+1.0}_{-0.4} events and calculate the upper limit B(tau- --> 2omega pi- nu_tau) < 5.4x10^{-7} at the 90% confidence level. This is the first upper limit for this mode.