A Limit on the Mass of the $\nu_{\tau}$

TL;DR

This paper sets an upper limit on the tau neutrino mass using a large dataset of tau pairs from electron-positron collisions, employing a likelihood analysis that accounts for background contributions.

Contribution

It introduces a novel likelihood method that explicitly includes background effects to constrain the tau neutrino mass.

Findings

Upper limit of 30 MeV/c^2 at 95% confidence level

Analyzed 4.5 million tau pairs from 5.0 fb^{-1} data

First explicit background inclusion in neutrino mass measurement

Abstract

A limit on the mass of the tau neutrino is derived from 4.5 million tau pairs produced in an integrated luminosity of 5.0 fb^{-1} of electron-positron annihilation to tau pairs at center of mass energies near 10.6 GeV. The measurement technique involves a two-dimensional extended likelihood analysis, including the dependence of the end-point population on the neutrino mass, and allows for the first time an explicit background contribution. We use the decays of the tau to five charged pions and a neutrino as well as the decay to three charged pions, two neutral pions and a neutrino to obtain an upper limit of 30 MeV/c^2 at 95% C.L.