First observation of two-neutrino double electron capture in $^{124}$Xe with XENON1T
Creators: name: Aprile, E.
name: Aalbers, J.
name: Agostini, F.
name: Alfonsi, M.
name: Althueser, L.
name: Amaro, F. D.
name: Anthony, M.
name: Antochi, V. C.
name: Arneodo, F.
name: Baudis, L.
name: Bauermeister, B.
name: Benabderrahmane, M. L.
name: Berger, T.
name: Breur, P. A.
name: Brown, A.
name: Brown, A.
name: Brown, E.
name: Bruenner, S.
name: Bruno, G.
name: Budnik, R.
name: Capelli, C.
name: Cardoso, J. M. R.
name: Cichon, D.
name: Coderre, D.
name: Colijn, A. P.
name: Conrad, J.
name: Cussonneau, J. P.
name: Decowski, M. P.
name: de Perio, P.
name: Di Gangi, P.
name: Di Giovanni, A.
name: Diglio, S.
name: Elykov, A.
name: Eurin, G.
name: Fei, J.
name: Ferella, A. D.
name: Fieguth, A.
name: Fulgione, W.
name: Rosso, A. Gallo
name: Galloway, M.
name: Gao, F.
name: Garbini, M.
name: Grandi, L.
name: Greene, Z.
name: Hasterok, C.
name: Hogenbirk, E.
name: Howlett, J.
name: Iacovacci, M.
name: Itay, R.
name: Joerg, F.
name: Kazama, S.
name: Kaminsky, B.
name: Kish, A.
name: Koltman, G.
name: Kopec, A.
name: Landsman, H.
name: Lang, R. F.
name: Levinson, L.
name: Lin, Q.
name: Lindemann, S.
name: Lindner, M.
name: Lombardi, F.
name: Lopes, J. A. M.
name: Fune, E. López
name: Macolino, C.
name: Mahlstedt, J.
name: Manfredini, A.
name: Marignetti, F.
name: Undagoitia, T. Marrodán
name: Masbou, J.
name: Masson, D.
name: Mastroianni, S.
name: Messina, M.
name: Micheneau, K.
name: Miller, K.
name: Molinario, A.
name: Morå, K.
name: Murra, M.
name: Naganoma, J.
name: Ni, K.
name: Oberlack, U.
name: Odgers, K.
name: Pelssers, B.
name: Peres, R.
name: Piastra, F.
name: Pienaar, J.
name: Pizzella, V.
name: Plante, G.
name: Podviianiuk, R.
name: Priel, N.
name: Qiu, H.
name: García, D. Ramírez
name: Reichard, S.
name: Riedel, B.
name: Rizzo, A.
name: Rocchetti, A.
name: Rupp, N.
name: Santos, J. M. F. dos
name: Sartorelli, G.
name: Šarčević, N.
name: Scheibelhut, M.
name: Schindler, S.
name: Schreiner, J.
name: Schulte, D.
name: Schumann, M.
name: Lavina, L. Scotto
name: Selvi, M.
name: Shagin, P.
name: Shockley, E.
name: Silva, M.
name: Simgen, H.
name: Therreau, C.
name: Thers, D.
name: Toschi, F.
name: Trinchero, G.
name: Tunnell, C.
name: Upole, N.
name: Vargas, M.
name: Wack, O.
name: Wang, H.
name: Wang, Z.
name: Wei, Y.
name: Weinheimer, C.
name: Wenz, D.
name: Wittweg, C.
name: Wulf, J.
name: Xu, Z.
name: Ye, J.
name: Zhang, Y.
name: Zhu, T.
name: Zopounidis, J. P.
Publisher: name: arXiv
Year: 2019
Subjects: subject: Nuclear Experiment (nucl-ex)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: Two-neutrino double electron capture ($2ν$ECEC) is a second-order Weak process with predicted half-lives that surpass the age of the Universe by many orders of magnitude. Until now, indications for $2ν$ECEC decays have only been seen for two isotopes, $^{78}$Kr and $^{130}$Ba, and instruments with very low background levels are needed to detect them directly with high statistical significance. The $2ν$ECEC half-life provides an important input for nuclear structure models and its measurement represents a first step in the search for the neutrinoless double electron capture processes ($0ν$ECEC). A detection of the latter would have implications for the nature of the neutrino and give access to the absolute neutrino mass. Here we report on the first direct observation of $2ν$ECEC in $^{124}$Xe with the XENON1T Dark Matter detector. The significance of the signal is $4.4σ$ and the corresponding half-life $T_{1/2}^{2ν\text{ECEC}} = (1.8\pm 0.5_\text{stat}\pm 0.1_\text{sys})\times 10^{22}\;\text{y}$ is the longest ever measured directly. This study demonstrates that the low background and large target mass of xenon-based Dark Matter detectors make them well suited to measuring other rare processes as well, and it highlights the broad physics reach for even larger next-generation experiments.