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.