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

Author(s): Agostini, M; Altenmüller, K; Appel, S; Atroshchenko, V; Bagdasarian, Z; et al

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Abstract: <jats:title>Abstract</jats:title><jats:p>Cosmogenic radio-nuclei are an important source of background for low-energy neutrino experiments. In Borexino, cosmogenic <jats:inline-formula><jats:alternatives><jats:tex-math>$$^{11}$$</jats:tex-math><mml:math xmlns:mml=""> <mml:msup> <mml:mrow /> <mml:mn>11</mml:mn> </mml:msup> </mml:math></jats:alternatives></jats:inline-formula>C decays outnumber solar <jats:italic>pep</jats:italic> 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 <jats:inline-formula><jats:alternatives><jats:tex-math>$$^{11}$$</jats:tex-math><mml:math xmlns:mml=""> <mml:msup> <mml:mrow /> <mml:mn>11</mml:mn> </mml:msup> </mml:math></jats:alternatives></jats:inline-formula>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 <jats:inline-formula><jats:alternatives><jats:tex-math>$$^{11}$$</jats:tex-math><mml:math xmlns:mml=""> <mml:msup> <mml:mrow /> <mml:mn>11</mml:mn> </mml:msup> </mml:math></jats:alternatives></jats:inline-formula>C tagging efficiency of <jats:inline-formula><jats:alternatives><jats:tex-math>$$\sim 90$$</jats:tex-math><mml:math xmlns:mml=""> <mml:mrow> <mml:mo>∼</mml:mo> <mml:mn>90</mml:mn> </mml:mrow> </mml:math></jats:alternatives></jats:inline-formula> % and <jats:inline-formula><jats:alternatives><jats:tex-math>$$\sim $$</jats:tex-math><mml:math xmlns:mml=""> <mml:mo>∼</mml:mo> </mml:math></jats:alternatives></jats:inline-formula> 63–66 % of the exposure surviving the tagging. We present also a novel technique that targets specifically <jats:inline-formula><jats:alternatives><jats:tex-math>$$^{11}$$</jats:tex-math><mml:math xmlns:mml=""> <mml:msup> <mml:mrow /> <mml:mn>11</mml:mn> </mml:msup> </mml:math></jats:alternatives></jats:inline-formula>C produced in high-multiplicity during major spallation events. Such <jats:inline-formula><jats:alternatives><jats:tex-math>$$^{11}$$</jats:tex-math><mml:math xmlns:mml=""> <mml:msup> <mml:mrow /> <mml:mn>11</mml:mn> </mml:msup> </mml:math></jats:alternatives></jats:inline-formula>C appear as a <jats:italic>burst</jats:italic> 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 <jats:inline-formula><jats:alternatives><jats:tex-math>$$\sim 90\%$$</jats:tex-math><mml:math xmlns:mml=""> <mml:mrow> <mml:mo>∼</mml:mo> <mml:mn>90</mml:mn> <mml:mo>%</mml:mo> </mml:mrow> </mml:math></jats:alternatives></jats:inline-formula> but with a higher fraction of the exposure surviving, in the range of <jats:inline-formula><jats:alternatives><jats:tex-math>$$\sim $$</jats:tex-math><mml:math xmlns:mml=""> <mml:mo>∼</mml:mo> </mml:math></jats:alternatives></jats:inline-formula> 66–68 %.</jats:p>
Publication Date: 7-Dec-2021
Electronic Publication Date: 7-Dec-2021
Citation: 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, XF, Di Ludovico, A, Di Noto, L, Drachnev, I, Formozov, A, Franco, D, Galbiati, C, Ghiano, C, Giammarchi, M, Goretti, A, Göttel, AS, 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, MT, 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, RB, von Feilitzsch, F, Wojcik, M, Wurm, M, Zavatarelli, S, Zuber, K, Zuzel, G. (2021). Identification of the cosmogenic $$^{11}$$C background in large volumes of liquid scintillators with Borexino. The European Physical Journal C, 81 (12), 10.1140/epjc/s10052-021-09799-x
DOI: doi:10.1140/epjc/s10052-021-09799-x
ISSN: 1434-6044
EISSN: 1434-6052
Language: en
Type of Material: Journal Article
Journal/Proceeding Title: The European Physical Journal C
Version: Final published version. This is an open access article.

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