Borexino, a liquid scintillator detector at LNGS, is designed for the detection of neu- trinos and antineutrinos from the Sun, supernovae, nuclear reactors, and the Earth. The feeble nature of these signals requires a strong suppression of backgrounds below a few MeV. Very low intrinsic radiogenic contamination of all detector components needs to be accompanied by the ef- ficient identification of muons and of muon-induced backgrounds. Muons produce unstable nuclei by spallation processes along their trajectory through the detector whose decays can mimic the expected signals; for isotopes with half-lives longer than a few seconds, the dead time induced by a muon-related veto becomes unacceptably long, unless its application can be restricted to a sub-volume along the muon track. Consequently, not only the identification of muons with very high efficiency but also a precise reconstruction of their tracks is of primary importance for the physics program of the experiment. The Borexino inner detector is surrounded by an outer water- Cherenkov detector that plays a fundamental role in accomplishing this task. The detector design principles and their implementation are described. The strategies adopted to identify muons are re- viewed and their efficiency is evaluated. The overall muon veto efficiency is found to be 99.992 % or better. Ad-hoc track reconstruction algorithms developed are presented. Their performance is tested against muon events of known direction such as those from the CNGS neutrino beam, test tracks available from a dedicated External Muon Tracker and cosmic muons whose angular dis- tribution reflects the local overburden profile. The achieved angular resolution is ∼3◦-5◦ and the lateral resolution is ∼35-50 cm, depending on the impact parameter of the crossing muon. The methods implemented to efficiently tag cosmogenic neutrons are also presented.
Muon and cosmogenic neutron detection in Borexino / G. Bellini, J. Benziger, D. Bick, S. Bonetti, M. Buizza Avanzini, B. Caccianiga, L. Cadonati, F. Calaprice, C. Carraro, A. Chavarria, A. Chepurnov, D. D'Angelo, S. Davini, A. Derbin, A. Etenko, F. von Feilitzsch, K. Fomenko, D. Franco, C. Galbiati, S. Gazzana, C. Ghiano, M. Giammarchi, M. Goeger-Neff, A. Goretti, E. Guardincerri, S. Hardy, A. Ianni, A. Ianni, M. Joyce, V. Kobychev, Y. Koshio, D. Korablev, G. Korga, D. Kryn, M. Laubenstein, C. Lendvai, T. Lewke, E. Litvinovich, B. Loer, F. Lombardi, P. Lombardi, L. Ludhova, I. Machulin, S. Manecki, W. Maneschg, G. Manuzio, Q. Meindl, E. Meroni, L. Miramonti, M. Misiaszek, D. Montanari, V. Muratova, L. Oberauer, M. Obolensky, F. Ortica, M. Pallavicini, L. Papp, L. Perasso, S. Perasso, A. Pocar, R. S. Raghavan, G. Ranucci, A. Razeto, A. Re, A. Romani, D. Rountree, A. Sabelnikov, R. Saldanha, C. Salvo, S. Schönert, H. Simgen, M. Skorokhvatov, O. Smirnov, A. Sotnikov, S. Sukhotin, Y. Suvorov, R. Tartaglia, G. Testera, D. Vignaud, R. B. Vogelaar, J. Winter, M. Wojcik, A. Wright, M. Wurm, J. Xu, O. Zaimidoroga, S. Zavatarelli, G. Zuzel. - In: JOURNAL OF INSTRUMENTATION. - ISSN 1748-0221. - 6:5(2011 May), pp. P05005.1-P05005.38.
Muon and cosmogenic neutron detection in Borexino
G. Bellini;S. Bonetti;M. Buizza Avanzini;D. D'Angelo;E. Meroni;L. Miramonti;A. Re;
2011
Abstract
Borexino, a liquid scintillator detector at LNGS, is designed for the detection of neu- trinos and antineutrinos from the Sun, supernovae, nuclear reactors, and the Earth. The feeble nature of these signals requires a strong suppression of backgrounds below a few MeV. Very low intrinsic radiogenic contamination of all detector components needs to be accompanied by the ef- ficient identification of muons and of muon-induced backgrounds. Muons produce unstable nuclei by spallation processes along their trajectory through the detector whose decays can mimic the expected signals; for isotopes with half-lives longer than a few seconds, the dead time induced by a muon-related veto becomes unacceptably long, unless its application can be restricted to a sub-volume along the muon track. Consequently, not only the identification of muons with very high efficiency but also a precise reconstruction of their tracks is of primary importance for the physics program of the experiment. The Borexino inner detector is surrounded by an outer water- Cherenkov detector that plays a fundamental role in accomplishing this task. The detector design principles and their implementation are described. The strategies adopted to identify muons are re- viewed and their efficiency is evaluated. The overall muon veto efficiency is found to be 99.992 % or better. Ad-hoc track reconstruction algorithms developed are presented. Their performance is tested against muon events of known direction such as those from the CNGS neutrino beam, test tracks available from a dedicated External Muon Tracker and cosmic muons whose angular dis- tribution reflects the local overburden profile. The achieved angular resolution is ∼3◦-5◦ and the lateral resolution is ∼35-50 cm, depending on the impact parameter of the crossing muon. The methods implemented to efficiently tag cosmogenic neutrons are also presented.File | Dimensione | Formato | |
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