M. Ambrosio, R. Antolini, C. Aramo, G. Auriemma, A. Baldini, G. C. Barbarino, B. C. Barish, G. Battistoni, R. Bellotti, C. Bemporad, E. Bernardini, P. Bernardini, H. Bilokon, V. Bisi, C. Bloise, C. Bower, S. Bussino, F. Cafagna, M. Calicchio, D. Campana, M. Carboni, M. Castellano, S. Cecchini, F. Cei, V. Chiarella, B. C. Choudhary, S. Coutu, L. De Benedictis, G. De Cataldo, H. Dekhissi, C. De Marzo, I. De Mitri, J. Derkaoui, M. De Vincenzi, A. Di Credico, E. Diehl, O. Erriquez, C. Favuzzi, C. Forti, P. Fusco, G. Giacomelli, G. Giannini , N. Giglietto, M. Giorgini, M. Grassi, L. Gray, A. Grillo, F. Guarino, P. Guarnaccia, C. Gustavino, A. Habig, K. Hanson, R. Heinz, Y. Huang, E. Iarocci, E. Katsavounidis, I. Katsavounidis, E. Kearns, H. Kim, S. Kyriazopoulou, E. Lamanna, C. Lane, T. Lari, D. S. Levin, P. Lipari, N. P. Longley, M. J. Longo, F. Maaroufi, G. Mancarella, G. Mandrioli, S. Manzoor, A. Margiotta Neri, A. Marini, D. Martello, A. Marzari-Chiesa, M. N. Mazziotta, C. Mazzotta, D. G. Michael, S. Mikheyev, L. Miller, P. Monacelli, T. Montaruli, M. Monteno, S. Mufson, J. Musser, D. Nicoló, C. Orth, G. Osteria, M. Ouchrif, O. Palamara, V. Patera, L. Patrizii, R. Pazzi, C. W. Peck, S. Petrera, P. Pistilli, V. Popa, A. Rainò, A. Rastelli, J. Reynoldson, F. Ronga, A. Sanzgiri, C. Satriano, L. Satta, E. Scapparone, K. Scholberg, A. Sciubba, P. Serra-Lugaresi, M. Severi, M. Sioli, M. Sitta, P. Spinelli, M. Spinetti, M. Spurio, R. Steinberg, J. L. Stone, L. R. Sulak, A. Surdo, G. Tarlè, V. Togo, D. Ugolotti, M. Vakili, C. W. Walter, and R. Webb.

We present a measurement of the underground decoherence function using multi-muon events observed in the MACRO detector at Gran Sasso at an average depth of 3800 hg/cm(2). Muon pair separations up to 70 m have been measured, corresponding to parent mesons with P-perpendicular to less than or equal to 1-2 GeV/c. Improved selection criteria are used to reduce detector effects mainly in the low distance separation region of muon pairs. Special care is given to a new unfolding procedure designed to minimize systematic errors in the numerical algorithm. The accuracy of the measurement is such that the possible contribution of rare processes, such as mu (+/-) + N --> mu (+/-) + N mu (+) + mu (-), can be experimentally studied. The measured decoherence function is compared with the predictions of the hadronic interaction model of the HEMAS Monte Carlo code. Good agreement is obtained. We interpret this agreement to indicate that no anomalous P-perpendicular to components in soft hadron-nucleus and nucleus-nucleus collisions are required by the MACRO experimental data. Preliminary comparisons with other Monte Carlo codes point out that the uncertainties associated with the hadronic interaction model may be as large as 20%, depending on the energy. MACRO data can be used as a benchmark for future work on the discrimination of shower models in the primary energy region around and below the knee of the spectrum. [50556-2821(99)03011-8].

With the aim of discussing the effect of the possible sources of systematic uncertainties in simulation models, the analysis of multiple muon events from the MACRO experiment at Gran Sasso is reviewed. In particular, the predictions from different currently available hadronic interaction models are compared.

We perform an indirect search for Weakly Interacting Massive Particles (WIMPs) using the MACRO detector to look for neutrino-induced upward-going muons resulting from the annihilation of WIMPs trapped in the Sun and Earth. The search is conducted in various angular cones centered on the Sun and Earth to accommodate a range of WIMP masses. No significant excess over the background from atmospheric neutrinos is seen and limits are placed on the upward-going muon fluxes from Sun and Earth. These limits are used to constrain neutralino particle parameters from supersymmetric theory, including those suggested by recent results from DAMA/NaI.

Using data collected by the MACRO experiment during the years 1989-1996, we show evidence for the shadow of the Moon in the underground cosmic ray flux with a significance of 3.6 sigma. This detection of the shadowing effect is the first by an underground detector. A maximum-likelihood analysis is used to determine that the angular resolution of the apparatus is 0.9 degrees +/- 0.3 degrees. These results demonstrate MACRO's capabilities as a muon telescope by confirming its absolute pointing ability and quantifying its angular resolution.

We have measured directly the residual energy of cosmic ray muons crossing the MACRO detector at the Gran Sasso Laboratory. For this measurement we have used a transition radiation detector consisting of three identical modules, each of about 12 m2 area, operating in the energy region from 100 GeV to 1 TeV. The results presented here were obtained with the first module collecting data for more than two years. The average single muon energy is found to be 320 ± 4 (stat.) ± 11 (syst.) GeV in the rock depth range 3000–6500 hg/cm2. The results are in agreement with calculations of the energy loss of muons in the rock above the detector.

An experimental study of the production of up-going charged particles in inelastic interactions of down-going underground muons is reported, using data obtained from the MACRO detector at the Gran Sasso Laboratory. In a sample of 12.2 x 10(6) single muons, corresponding to a detector lifetime of 1.55y, 243 events are observed having an up-going particle associated with a down-going muon. These events are analysed to determine the range and emission angle distributions of the up-going particle, corrected for detection and reconstruction efficiency.Measurements of the muon neutrino flux by underground detectors are often based on the observation of through-going and stopping muons produced in v(mu) interactions in the rock below the detector. Up-going particles produced by an undetected down-going muon are a potential background source in these measurements. The implications of this background for neutrino studies using MACRO are discussed. (C) 1998 Elsevier Science B.V.

The MACRO experiment has been running as a supernova neutrino detector since 1989 and is sensitive to the whole galaxy since the beginning of 1992. A galactic supernova would produce some hundreds of νe events in the detector. We describe our stellar gravitational collapse online monitors and alarm system, and present the results of a search for neutrino bursts from supernovae during a period of 1.5 yr.

We present a measurement of the flux of neutrino-induced upgoing muons (< E-nu > similar to 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 less than or equal to cos theta less than or equal to -0.1 does not fit well with the no oscillation expectation, giving a maximum probability for chi(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 distribution can be explained by a neutrino oscillation hypothesis. Fitting either the flux or zenith distribution independently yields mixing parameters of sin(2)2 theta = 1.0 and Delta m(2) of a few times 10(-3) eV(2). However, the observed zenith distribution does not fit well with any expectations, giving a maximum probability for chi(2) of 5% for the beat oscillation hypothesis, and the combined probability for the shape and number of events is 17%. We conclude that these data favor a neutrino oscillation hypothesis, but with unexplained structure in the zenith distribution not easily explained by either the statistics or systematics of the experiment. (C) 1998 Published by Elsevier Science B.V. All rights reserved.

The multimuon data collected by the MACRO detector at Gran Sasso have been analyzed using a new method. The resulting all-particle spectrum is consistent with EAS measurements but higher and flatter than the one obtained from direct experiments.

MACRO is designed to make a multiply redundant search for GUT magnetic monopoles over a wide velocity range. The 100 MHz pulse height recorder and synchronous encoder (PHRASE) and the energy reconstruction processor (ERP) are two components of that search, both based on the MACRO liquid scintillator. They are sensitive to monopoles with or without captured nuclei in the range β ∼ 10−3 to β ∼ 1. Here, the performance of these systems is discussed, including also analysis methods and background evaluations.

In this paper, the first of a two-part work, we present the reconstruction and measurement of muon events detected underground by the MACRO experiment at Gran Sasso (E-mu greater than or equal to 1.3 TeV in atmosphere). The main aim of this work is to discuss the muon multiplicity distribution as measured in the detector. The data sample analyzed consists of 4.4 x 10(6) muon events, of which similar to 263 000 are multiple muons, corresponding to a total live time of 5850 h. In this sample, the observed multiplicities extend above N-mu = 35, with intermuon separations up to 50 m and beyond. Additional complementing measurements, such as the inclusive muon Aux, the angular distribution, and the muon separation distribution (decoherence), are also included. The physical interpretation of the results presented here is reported in the following companion paper.

Using 5.33 x lo6 single muons collected in 1.46 x lo4 live hours by MACRO during the period 19911994, we have searched for a correlation between variations in the underground muon rate, N,, 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, a~ = (T/N,) (aN,/aT) = 0.83 f 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 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. @ 1997 Elsevier Science B.V.

Multimuon data from the MACRO experiment at Gran Sasso have been analyzed using a new method, which allows one to estimate the primary cosmic ray fluxes. The estimated all-particle spectrum is higher and flatter than the one obtained from direct measurements but is consistent with EAS array measurements. The spectral indexes of the fitted energy spectrum are 2.56 +/- 0.05 for E < 500 TeV and 2.9 +/- 0.3 for E > 5000 TeV with a gradual change at intermediate energies. The average mass number shows little dependence on the primary energy below 1000 TeV, with a value of 10.1 +/- 2.5 at 100 TeV. At higher energies the best fit average mass shows a mild increase with energy, even though no definite conclusion can be reached taking into account errors. The fitted spectra cover a range from similar to 50 TeV up to several thousand TeV.

The MACRO underground experiment performed a systematic experimental study of muon bundle structure. The aim is to gain a better understanding of the features of high energy cosmic ray interactions. The reliability of the hadronic interaction model in reproducing the shower development features at the highest energy can be studied selecting high multiplicity muon bundles. We present here the analisys of the muon lateral distribution (decoherence function) based on two different method( detector dependent and detector independent method), the decoherence function in a high multiplicity event subsample and the search for muon clusters.

Upward-going muon events collected with the lower half of the MACRO detector have been analyzed in order to search for Weakly Interacting Massive Particles possibly trapped in the core of the Sun and of the Earth. No statistically significant signal could be discriminated over the possible fluctuations of the atmospheric neutrino background. Assuming a particular neutralino model, the explorable neutralino mass region has been considered.