Measurement of atmospheric neutrino composition with the IMB-3 detector

The atmospheric neutrino flux is measured using a 3.4-kt yr exposure of the IMB-3 detector. Single-ring events are classified as showering or nonshowering using the geometry of the Cerenkov pattern. A simulation of neutrino interactions and three models of atmospheric neutrino production are used to predict the composition of the sample. The showering- nonshowering character is strongly correlated with the flavor of the neutrino parent. In the lepton momentum range of p less than 1500 MeV/c, it is found that nonshowering events comprise /41 + or - 3(stat) + or - 2(syst)/ percent of the total. The fraction expected is /51 + or - 5(syst)/ percent. (Author)