Experimental upper limit to the galactic stellar-collapse rate

A search is made for bursts of low-energy (20–60 MeV) neutrino interactions, signaling stellar core collapse, in a large underground water-Čerenkov detector. Over a period of 5.6 years (2.1 live years) no bursts were observed. A 90%-confidence-level (C.L.) upper limit to the rate of stellar collapse in the Galaxy is set at <1.5 ${\mathrm{yr}}^{\mathrm{-}1}$. A limit of <1.1 stellar collapses per year (90% C.L.) is set for a smaller volume of the Galaxy (10 kpc radius) which includes the Galactic center and >50% of the stars in the Milky Way.