Probing Majorana neutrinos with double-β decay

Agostini, M.; Bakalyarov, A. M.; Balata, M.; Barabanov, I.; Baudis, L.; Bauer, C.; Bellotti, E.; Belogurov, S.; Bettini, A.; Bezrukov, L.; Borowicz, D.; Brudanin, V.; Brugnera, R.; Caldwell, A.; Cattadori, C.; Chernogorov, A.; Comellato, T.; D'Andrea, V.; Demidova, E. V.; Di Marco, N.; Domula, A.; Doroshkevich, E.; Egorov, V.; Falkenstein, R.; Fomina, M.; Gangapshev, A.; Garfagnini, A.; Giordano, M.; Grabmayr, P.; Gurentsov, V.; Gusev, K.; Hakenmuller, J.; Hegai, A.; Heisel, M.; Hemmer, S.; Hiller, R.; Hofmann, W.; Hult, M.; Inzhechik, L. V.; Csathy, J. J.; Jochum, J.; Junker, M.; Kazalov, V.; Kermaidic, Y.; Kihm, T.; Kirpichnikov, I. V.; Kirsch, A.; Kish, A.; Klimenko, A.; Kneissl, R.; Knopfle, K. T.; Kochetov, O.; Kornoukhov, V. N.; Krause, P.; Kuzminov, V. V.; Laubenstein, M.; Lazzaro, A.; Lindner, M.; Lippi, I.; Lubashevskiy, A.; Lubsandorzhiev, B.; Lutter, G.; Macolino, C.; Majorovits, B.; Maneschg, W.; Miloradovic, M.; Mingazheva, R.; Misiaszek, M.; Moseev, P.; Nemchenok, I.; Panas, K.; Pandola, L.; Pelczar, K.; Pertoldi, L.; Piseri, P.; Pullia, A.; Ransom, C.; Riboldi, S.; Rumyantseva, N.; Sada, C.; Sala, E.; Salamida, F.; Schmitt, C.; Schneider, B.; Schonert, S.; Schutz, A. -K.; Schulz, O.; Schwarz, M.; Schwingenheuer, B.; Selivanenko, O.; Shevchik, E.; Shirchenko, M.; Simgen, H.; Smolnikov, A.; Stanco, L.; Stukov, D.; Vanhoefer, L.; Vasenko, A. A.; Veresnikova, A.; Von Sturm, K.; Wagner, V.; Wegmann, A.; Wester, T.; Wiesinger, C.; Wojcik, M.; Yanovich, E.; Zhitnikov, I.; Zhukov, S. V.; Zinatulina, D.; Zschocke, A.; Zsigmond, A. J.; Zuber, K.; Zuzel, G.

doi:10.1126/science.aav8613

A discovery that neutrinos are Majorana fermions would have profound implications for particle physics and cosmology. The Majorana character of neutrinos would make possible the neutrinoless double-beta (0 nu beta beta) decay, a matter-creating process without the balancing emission of antimatter. The GERDA Collaboration searches for the 0 nu beta beta decay of Ge-76 by operating bare germanium detectors in an active liquid argon shield. With a total exposure of 82.4 kg.year, we observe no signal and derive a lower half-life limit of T-1/2 > 0.9 x 10(26) years (90% C.L.). Our T-1/2 sensitivity, assuming no signal, is 1.1 x 10(26) years. Combining the latter with those from other 0 nu beta beta decay searches yields a sensitivity to the effective Majorana neutrino mass of 0.07 to 0.16 electron volts.