An upper limit for the tau-neutrino mass from tau --> 5 pi+- nu_tau decays

TL;DR

This paper establishes an upper limit on the tau-neutrino mass by analyzing tau decays into five pions and neutrinos, combining data from 1991-1995 with previous measurements, resulting in a limit of 27.6 MeV at 95% CL.

Contribution

It provides the first upper limit from tau -> 5pi+- nu_tau decays and improves the overall tau-neutrino mass constraint by combining multiple decay channels.

Findings

Upper limit of 43.2 MeV from tau -> 5pi+- nu_tau decays

Combined limit of 27.6 MeV on tau-neutrino mass

Analysis used data from OPAL detector at LEP

Abstract

An upper limit for the tau-neutrino mass has been determined from the decay tau -> 5pi+- \nu_tau using data collected with the OPAL detector from 1991 to 1995 in e+e- collisions at \sqrt{s} ~ M_Z. A limit of 43.2 MeV at 95% CL is obtained using a two-dimensional method in the 5pi invariant mass and energy distribution from 22 selected events. Combining this result with OPAL's previously published measurement using tau+tau- -> 3h+- \bar{nu}_tau 3h-+ \nu_tau decays, a new combined limit of m_{nu_tau} < 27.6 MeV (95% CL) is obtained.