Atmospheric neutrino induced muons in the MACRO detector

A measurement of the flux of neutrino-induced muons using the MACRO detecto r is presented. Different event topologies, corresponding to different neut rino parent energies can be detected. The upward throughgoing muon sample i s larger event sample. For this sample, produced by neutrinos having an ave rage energy around 100 GeV, the ratio of the number of observed to expected events integrated over all zenith angles is 0.74 +/- 0.036(stat) +/- 0.046 (syst) +/- 0.13(theor). We have investigated whether the observed number of events and the shape of the zenith distribution can be explained by an hyp othesis of v(mu) --> v(tau) oscillation. The best probability (17%) is obta ined for sin(2) 2 theta similar or equal to 1.0 and Delta m(2) of a few tim es 10(-3) eV(2), while the probability for the no oscillation hypothesis is 0.1 %. The other samples are due to the internally produced events and to upward-going stopping muons; the average parent neutrino energy is of the o rder of 4 GeV. The low energy data sets show a deficit of observed events s imilar to the one predicted by the oscillation model with maximum mixing su ggested from the upward throughgoing muon sample.