Identification of the cosmogenic 11C background in large volumes of liquid scintillators with Borexino

• Published in: The European physical journal. C, Particles and fields Particles and fields, 2021-12, Vol.81 (12)
• Main Authors: Agostini, M., Altenmüller, K., Appel, S., Atroshchenko, V., Bagdasarian, Z., Basilico, D., Bellini, G., Benziger, J., Biondi, R., Bravo, D., Caccianiga, B., Calaprice, F., Caminata, A., Cavalcante, P., Chepurnov, A., D’Angelo, D., Davini, S., Derbin, A., Di ZGiacintio, A., Di Marcello, V., Ding, X. F., Di Ludovico, A., Di Noto, L., Drachnev, I., Formozov, A., Franco, D., Galbiati, C., Ghiano, C., Giammarchi, M., Goretti, A., Göttel, A. S., Gromov, M., Guffanti, D., Ianni, Aldo, Ianni, Andrea, Jany, A., Jeschke, D., Kobychev, V., Korga, G., Kumaran, S., Laubenstein, M., Litvinovich, E., Lombardi, P., Lomskaya, I., Ludhova, L., Lukyanchenko, G., Lukyanchenko, L., Machulin, I., Martyn, J., Meroni, E., Meyer, M., Miramonti, L., Misiaszek, M., Muratova, V., Neumair, B., Nieslony, M., Nugmanov, R., Oberauer, L., Orekhov, V., Ortica, F., Pallavicini, M., Papp, L., Pelicci, L., Penek, Ö., Pietrofaccia, L., Pilipenko, N., Pocar, A., Porcelli, A., Raikov, G., Ranalli, M. T., Ranucci, G., Razeto, A., Re, A., Redchuk, M., Romani, A., Rossi, N., Schönert, S., Semenov, D., Settanta, G., Skorokhvatov, M., Singhal, A., Smirnov, O., Sotnikov, A., Suvorov, Y., Tartaglia, R., Testera, G., Thurn, J., Unzhakov, E., Vishneva, A., Vogelaar, R. B., von Feilitzsch, F., Wojcik, M., Wurm, M., Zavatarelli, S., Zuber, K., Zuzel, G.
• Format: Article
• Language: English
• Subjects: Astronomy; Astrophysics and Cosmology; Elementary Particles; Hadrons; Heavy Ions; Marking; Measurement Science and Instrumentation; Muons; Nuclear Energy; Nuclear Physics; Physics; Physics and Astronomy; Quantum Field Theories; Quantum Field Theory; Regular Article - Experimental Physics; Scintillation counters; Solar neutrinos; Spacetime; Spallation; String Theory
• ISSN: 1434-6044; 1434-6052
• DOI: 10.1140/epjc/s10052-021-09799-x

Cosmogenic radio-nuclei are an important source of background for low-energy neutrino experiments. In Borexino, cosmogenic 11 C decays outnumber solar pep and CNO neutrino events by about ten to one. In order to extract the flux of these two neutrino species, a highly efficient identification of this background is mandatory. We present here the details of the most consolidated strategy, used throughout Borexino solar neutrino measurements. It hinges upon finding the space-time correlations between 11 C decays, the preceding parent muons and the accompanying neutrons. This article describes the working principles and evaluates the performance of this Three-Fold Coincidence (TFC) technique in its two current implementations: a hard-cut and a likelihood-based approach. Both show stable performances throughout Borexino Phases II (2012–2016) and III (2016–2020) data sets, with a 11 C tagging efficiency of ∼ 90  % and ∼  63–66 % of the exposure surviving the tagging. We present also a novel technique that targets specifically 11 C produced in high-multiplicity during major spallation events. Such 11 C appear as a burst of events, whose space-time correlation can be exploited. Burst identification can be combined with the TFC to obtain about the same tagging efficiency of ∼ 90 % but with a higher fraction of the exposure surviving, in the range of ∼  66–68 %.