Limits on the Mass of the Tau Neutrino from CLEO

TL;DR

This paper establishes an upper limit on the tau neutrino mass using a large dataset from CLEO, employing a likelihood analysis that accounts for background contributions in tau decay channels.

Contribution

It introduces a novel likelihood analysis method that explicitly includes background effects to set a new upper limit on the tau neutrino mass.

Findings

Upper limit of 30 MeV on tau neutrino mass from specific decay channels

Preliminary limit of 31 MeV from tau decay to 3 charged hadrons

First explicit background inclusion in neutrino mass measurement

Abstract

A limit on the mass of the tau neutrino is derived from 4.5x10^6 tau pairs produced at a center of mass energy of 10.6 GeV. The measurement technique involves a two-dimensional extended likelihood analysis, including the dependence of the end-point population on the tau 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 and to 3 charged pions, 2 neutral pions and a neutrino to obtain an upper limit of 30 MeV, as well as a preliminary limit of 31 MeV from the decay of a tau to 3 charged hadrons, a neutral pi and a neutrino.