The Kolar Gold Fields neutrino project

Abstract

In the underground laboratory at a depth of 7 600 ft in the Kolar Gold Mines, South India, five telescopes have been in operation for a study of the cosmic radiation which penetrates to such depths. In an exposure of 677 400 m2 sr h (for isotropic radiation) 46 events have been recorded. In seven events the particle trajectory has a projected zenith angle larger than 50°; these are interpreted as due to muons produced by neutrino interactions in the surrounding rock. From this the rate of neutrino-induced events is estimated to be about 3.1 × 10−13/cm2 s sr.The bulk of events with projected zenith angles less than 40° are interpreted as due to atmospheric muons, from considerations of the expected intensity and angular distribution. In between the above-mentioned two groups, there are 10 events in the zenith angle interval 40°–50° compared with an expected number of events of about two. The difference between the observed and expected rates in this angular interval is discussed.Recently, two new solid-iron magnet spectrographs have been installed at the same level, for measuring the momentum and sign of charge of the muons traversing the detector system. Each spectrograph has a maximum detectable momentum of 20 GeV/c and a collecting power of about 35 m2 sr for isotropic radiation.