JUNO sensitivity to invisible decay modes of neutrons
Angel Abusleme, Thomas Adam, Kai Adamowicz, S. Ahmad, Rizwan Ahmed, S. Aiello, Fengpeng An, Qi An, Giuseppe Andronico, Н. Анфимов, V. Antonelli, Tatiana Antoshkina, J. P. A. M. de André, Didier Auguste, Weidong Bai, Nikita Balashov, W. Baldini, Andrea Barresi, D. Basilico, E. Baussan, Marco Bellato, Marco Beretta, Antonio Bergnoli, D. Bick, Lukas Bieger, S. Biktemerova, Thilo Birkenfeld, Iwan Blake, S.C. Blyth, Anastasia Bolshakova, M. Bongrand, D. Breton, A. Brigatti, R. Brugnera, Riccardo Bruno, A. Budano, José Busto, J. Busenitz, Barbara Caccianiga, Hao Cai, X. Cai, Yanke Cai, Zhiyan Cai, S. Callier, S. Calvez, Antonio Cammi, Agustín Campeny, Chuanya Cao, Guofu Cao, Jun Cao, R. Caruso, C. Cerna, Vanessa Cerrone, J. F. Chang, Yun Chang, Auttakit Chatrabhuti, Chao Chen, Guoming Chen, Pingping Chen, Shaomin Chen, Xin Chen, Yiming Chen, Yixue Chen, Yu Chen, Zelin Chen, Zhangming Chen, Zhiyuan Chen, Zikang Chen, Jie Cheng, Yaping Cheng, Yu Cheng, Alexander Chepurnov, Alexey Chetverikov, Davide Chiesa, P. Chimenti, Yen-Ting Chin, Po-Lin Chou, Ziliang Chu, A. Chukanov, Gérard Claverie, Catia Clementi, B. Clerbaux, Marta Colomer Molla, Selma Conforti Di Lorenzo, Alberto Coppi, Daniele Corti, Simon Csakli, Chenyang Cui, F. Dal Corso, Olivia Dalager, Jaydeep Datta, C. De La Taille, Zhi Deng, Ziyan Deng, Xiaoyu Ding, Xuefeng Ding, Yayun Ding, Bayu Dirgantara, Carsten Dittrich, Sergey Dmitrievsky
Abstract
Abstract We explore the decay of bound neutrons in the JUNO liquid scintillator detector into invisible particles (e.g., $$n\rightarrow 3 \nu $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>n</mml:mi> <mml:mo>→</mml:mo> <mml:mn>3</mml:mn> <mml:mi>ν</mml:mi> </mml:mrow> </mml:math> or $$nn \rightarrow 2 \nu $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>n</mml:mi> <mml:mi>n</mml:mi> <mml:mo>→</mml:mo> <mml:mn>2</mml:mn> <mml:mi>ν</mml:mi> </mml:mrow> </mml:math> ), which do not produce an observable signal. The invisible decay includes two decay modes: $$ n \rightarrow { inv} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>n</mml:mi> <mml:mo>→</mml:mo> <mml:mrow> <mml:mi>inv</mml:mi> </mml:mrow> </mml:mrow> </mml:math> and $$ nn \rightarrow { inv} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>n</mml:mi> <mml:mi>n</mml:mi> <mml:mo>→</mml:mo> <mml:mrow> <mml:mi>inv</mml:mi> </mml:mrow> </mml:mrow> </mml:math> . The invisible decays of s -shell neutrons in $$^{12}\textrm{C}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mmultiscripts> <mml:mrow/> <mml:mrow/> <mml:mn>12</mml:mn> </mml:mmultiscripts> <mml:mtext>C</mml:mtext> </mml:mrow> </mml:math> will leave a highly excited residual nucleus. Subsequently, some de-excitation modes of the excited residual nuclei can produce a time- and space-correlated triple coincidence signal in the JUNO detector. Based on a full Monte Carlo simulation informed with the latest available data, we estimate all backgrounds, including inverse beta decay events of the reactor antineutrino $${\bar{\nu }}_e$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mover> <mml:mrow> <mml:mi>ν</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>¯</mml:mo> </mml:mrow> </mml:mover> <mml:mi>e</mml:mi> </mml:msub> </mml:math> , natural radioactivity, cosmogenic isotopes and neutral current interactions of atmospheric neutrinos. Pulse shape discrimination and multivariate analysis techniques are employed to further suppress backgrounds. With two years of exposure, JUNO is expected to give an order of magnitude improvement compared to the current best limits. After 10 years of data taking, the JUNO expected sensitivities at a 90% confidence level are $$\tau /B( n \rightarrow { inv} ) > 5.0 \times 10^{31} \, \textrm{years}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>τ</mml:mi> <mml:mo>/</mml:mo> <mml:mi>B</mml:mi> <mml:mrow> <mml:mo>(</mml:mo> <mml:mi>n</mml:mi> <mml:mo>→</mml:mo> <mml:mrow> <mml:mi>inv</mml:mi> </mml:mrow> <mml:mo>)</mml:mo> </mml:mrow> <mml:mo>></mml:mo> <mml:mn>5.0</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mn>10</mml:mn> <mml:mn>31</mml:mn> </mml:msup> <mml:mspace/> <mml:mtext>years</mml:mtext> </mml:mrow> </mml:math> and $$\tau /B( nn \rightarrow { inv} ) > 1.4 \times 10^{32} \, \textrm{years}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>τ</mml:mi> <mml:mo>/</mml:mo> <mml:mi>B</mml:mi> <mml:mrow> <mml:mo>(</mml:mo> <mml:mi>n</mml:mi> <mml:mi>n</mml:mi> <mml:mo>→</mml:mo> <mml:mrow> <mml:mi>inv</mml:mi> </mml:mrow> <mml:mo>)</mml:mo> </mml:mrow> <mml:mo>></mml:mo> <mml:mn>1.4</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mn>10</mml:mn> <mml:mn>32</mml:mn> </mml:msup> <mml:mspace/> <mml:mtext>years</mml:mtext> </mml:mrow> </mml:math> .