Study of the Ultrahigh-energy Primary-cosmic-ray Composition With the Macro Experiment

Ahlen, S.; Ambrosio, M.; Antolini, R.; Auriemma, Giulio; Baldini, A.; Bam, B. B.; Barbarino, G. C.; Barish, B. C.; Battistoni, G.; Bellotti, R.; Bemporad, C.; Bernardini, P.; Bilokon, H.; Bisi, V.; Bloise, C.; Bussino, S.; Cafagna, F.; Calicchio, M.; Campana, P.; Campana, D.; Carboni, M.; Cecchini, S.; Cei, F.; Chiarella, V.; Chiera, C.; Cobis, A.; Cormack, R.; Corona, A.; Coutu, S.; Decataldo, G.; Demarzo, C.; Devincenzi, M.; Dicredico, A.; Diehl, E.; Erriquez, O.; Favuzzi, C.; Ficenec, D.; Forti, C.; Foti, L.; Fusco, P.; Giacomelli, G.; Giannini, G.; Giglietto, N.; Giubellino, P.; Grassi, M.; Green, P.; Grillo, A.; Guarino, F.; Gustavino, C.; Habig, A.; Heinz, R.; Hong, J. T.; Iarocci, E.; Katsavounidis, E.; Kearns, E.; Klein, S.; Kyriazopoulou, S.; Lamanna, E.; Lane, C.; Lee, C.; Levin, D.; Lipari, P.; Liu, G.; Liu, R.; Longo, M. J.; Ludlam, G.; Mancarella, G.; Mandrioli, G.; Margiottaneri, A.; Marin, A.; Marini, A.; Martello, D.; Martellotti, G.; Chiesa, A. M.; Masera, M.; Matteuzzi, P.; Michael, D. G.; Miller, L.; Monacelli, P.; Monteno, M.; Mufson, S.; Musser, J.; Nutter, S.; Okada, C.; Osteria, G.; Palamara, O.; Parlati, S.; Patera, V.; Patrizii, L.; Pazzi, R.; Peck, C. W.; Petrakis, J.; Petrera, S.; Pignatano, N. D.; Pistilli, P.; Predieri, F.; Ramello, L.; Reynoldson, J.; Ronga, F.; Rosa, G.; Satriano, Celestina; Satta, L.; Scapparone, E.; Scholberg, K.; Sciubba, A.; Lugaresi, P. S.; Severi, M.; Sitta, M.; Spinelli, P.; Spinetti, M.; Spurio, M.; Steele, J.; Steinberg, R.; Stone, J. L.; Sulak, L. R.; Surdo, A.; Tarle, G.; Togo, V.; Valente, V.; Verdone, G. R.; Walter, C. W.; Webb, R.; Worstell, W.

doi:10.1103/PhysRevD.46.895

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 approximately 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.