Upper limit on tau neutrino mass from τ → 5π(π0)ντ

An updated limit on the mντ has been derived from 295,000 η decays observed in the ALEPH detector at LEP between 1991 and 1994. The result is obtained from a maximum likelihood fit in the hadronic total energy vs hadronic invariant mass plane for a sample of selected 5π(π0) candidates consisting of 39 τ → 5πντ and 3 τ → 5ππ0ντ. A comparison of the invariant mass spectrum with 5π phase space and a a1 + 2π model favors the latter τ decay mechanism. The τ neutrino mass limit of 23.1 MeV at 95 % confidence level is slightly more restrictive that the published value. (author)