SEASONAL-VARIATIONS IN THE UNDERGROUND MUON INTENSITY AS SEEN BY MACRO

Using 5.33 x 10(6) single muons collected in 1.46 x 10(4) live hours b y MACRO during the period 1991-1994, we have searched for a correlatio n between variations in the underground muon rate, N-mu, and seasonal temperature variations in the atmosphere. These correlations are found to be present with high statistical significance. Analysis of the rel atively complete December 1992-December 1994 subset of the data yields a value for the temperature coefficient, alpha(T) = (T/N-mu)(partial derivative N-mu/partial derivative T) = 0.83 +/- 0.13. Analysis of the total data Set gives consistent results. We have compared this result with the hypothesis that the muons observed in MACRO come from pion d ecays alone. Although our result is consistent with the 'pion only' hy pothesis, a discussion of the sensitivity of our data sample to the ka on component of the cascades leading to observed muons underground wil l also be presented. (C) 1997 Elsevier Science B.V.