Detection of a rare event on 23 February 1987 by the neutrino radiation detector under Mont Blanc
Dadykin V. L. , Zatsepin G. T. , Korchagin V. B. , Korchagin P. V. , Mal'gin A. S. , Ryazhskaya O. G. , Ryasnyi V. G. , Talochkin V. P. , Khal'chukov F. F., Yakushev V. F. , Aglietta M. , Badino G. , Bologna G. , Castagnoli C. , Castellina A. , Fulgione W. , Galeotti P. , Saavedra O. , Trincero J., Vernetto S.
A rare event which was detected at 2h32m36s UT on 23 February 1987 by a liquid scintillation detector in a tunnel under Mont Blanc, at a depth of 5200 m water equivalent, is discussed. The active mass of the detector is about 90 metric tons. Over a time interval of 7 s, five pulses with amplitudes ranging from 7 to 11 MeV were detected. An upper limit of 0.7 yr~1 is estimated for the frequency at which such events would result from random fluctuations of the background. The possibility that this event is correlated with the supernova SN1987A in the Large Magellanic Cloud, which was observed at 9h UT on 23 February 1987, is not ruled out. Such a correlation would occur at random once in ~ 1000 yr.