R. Akers et al., DETERMINATION OF AN UPPER LIMIT FOR THE MASS OF THE TAU-NEUTRINO AT LEP, Zeitschrift fur Physik. C, Particles and fields, 65(2), 1995, pp. 183-188
An upper limit for the nu(tau) mass is determined through the kinemati
c reconstruction of the decay tau --> 5 pi(+/-)nu(tau) in the OPAL det
ector at LEP. The limit is obtained using a new method based on the co
mparison of the two-dimensional distribution of energy and invariant m
ass of the five-pion system with expectations from different neutrino
mass hypotheses. From a sample of five events surviving the selection
criteria we obtain an upper limit of 74 MeV at 95% confidence level. I
t is the first measurement at LEP energies, where the larger average m
ultiplicity of e(+)e(-) --> q (q) over bar events makes the suppressio
n of this background more robust compared to lower energies.