We have analyzed a sample of 1.8 x 10 exp 6 muons with E(mu) greater than about 1.3 TeV collected by the first and second supermodules of the MACRO detector at Gran Sasso during the period 1989 February to 1991 February. We have searched for an excess of muons of celestial origin over cosmic-ray background. Our search for steady sources in solid angle bins of 3.0 x 3.0 deg in the declination range -5 to 90 deg was negative; the upper limit with 95 percent C.L. to the muon flux at midlatitudes is less than about 2 x 10 exp -12/sq cm s. In addition, we have searched for muon excesses modulated by the orbital period of selected X-ray sources, including Cyg X-3, Cyg X-1, Her X-1, 4U 0115 + 63, and 4U 1907 + 09. We have no evidence of any bursting activity from Cyg X-3, during our search period, which includes the radio outburst of 1991 January
Systematic radon monitoring in the Gran Sasso Underground Laboratory was performed in order to determine the background radon contribution to the sophisticated experimental apparatus and to check health physics standards for the personnel. As expected, the radon concentrations were found to depend strongly on the ventilation in the three experimental halls. Considerable reductions in the radon concentrations were obtained in 1993, when fresh air was drawn into the laboratory through a pipe and exhaust air was routed into the highway tunnel.
We present the analysis of multiple-muon events collected with one supermodule (1013 h live time) and two supermodules (1195 h live time) of the MACRO detector at Gran Sasso, Italy. Multimuon rates are shown to be sensitive to primary-cosmic-ray energies between-50 TeV and several thousand TeV. Experimental data are compared with the expected rates from two composition models: a light (i.e. , proton-rich) and a heavy (i.e. , Fe-rich) composition. The predictions are based on a Monte Carlo simulation of the hadronic interactions of cosmic-ray nuclei, followed by a detailed tracking of the muons through the rock and the experimental apparatus. The results show good sensitivity of the MACRO detector to primary composition. The data exhibit a preference towards the light composition model.
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