Limits on $\nu_{\tau}$ mass by DELPHI

TL;DR

This paper sets an upper limit on the tau neutrino mass using LEP data from DELPHI, analyzing specific tau decay events to constrain the neutrino's mass to below 48 MeV/c^2 at 95% confidence.

Contribution

It provides a new experimental limit on the tau neutrino mass by analyzing decay topologies and applying a bidimensional fit to invariant mass and energy data.

Findings

Tau neutrino mass < 48.0 MeV/c^2 at 95% CL

Used all LEP DELPHI data from 1992-1995

Analyzed 1-5 topology tau decays

Abstract

A limit on the tau neutrino mass is obtained using all the $Z^{0} \to \tau^{+} \tau^{-}$ data collected at LEP by the DELPHI detector between 1992 and 1995. In this analysis events in which one of the taus decays into one charged particle, while the second $\tau$ decays into f{}ive charged pions (1-5 topology) have been used. The neutrino mass is determined from a bidimensional \fit ~on the invariant mass $m^{*}_{5 \pi}$ and on the energy $E_{5 \pi}$ of the f{}ive $\pi^{\pm}$ system. The result found is $m_{\nu_{\tau}}<$ 48.0 MeV/$c^{2}$ at 95% conf{}idence level.