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We present a measurement of the flux of neutrino-induced upgoing muons (∼ 100 GeV) using the MACRO detector. The ratio of the number of observed to expected events integrated over all zenith angles is 0.74 ±0.036(stat) ±0.046(systematic) ±0.13(theoretical). The observed zenith distribution for −1.0 ≤ cos θ ≤ −0.1 does not fit well with the no oscillation expectation, giving a maximum probability for χ 2 of 0.1%. The acceptance of the detector has been extensively studied using downgoing muons, independent analyses and Monte-Carlo simulations. The other systematic uncertainties cannot be the source of the discrepancies between the data and expectations.We have investigated whether the observed number of events and the shape of the zenith dis-1

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The vertical underground muon intensity has been measured in the slant depth range 3200-7000 hg cm(-2) (standard rock) with the completed lower part of the MACRO detector at the Gran Sasso laboratory, using a large sample of data. These observations are used to compute the surface muon flux and the primary ''all-nucleon'' spectrum. An analysis of systematic uncertainties introduced by the interaction models in the atmosphere and the underground propagation of muons is presented

Using 5.33 × 106 single muons collected in 1.46 × 104 live hours by MACRO during the period 1991–1994, we have searched for a correlation between variations in the underground muon rate, Nμ, and seasonal temperature variations in the atmosphere. These correlations are found to be present with high statistical significance. Analysis of the relatively complete December 1992–December 1994 subset of the data yields a value for the temperature coefficient, . 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 decays alone. Although our result is consistent with the ‘pion only’ hypothesis, a discussion of the sensitivity of our data sample to the kaon component of the cascades leading to observed muons underground will also be presented