Neutrinoless double beta decay (0νββ) is a yet unobserved nuclear process that would demonstrate Lepton number violation, a clear evidence of beyond standard model physics. The process two neutrino double beta decay (2νββ) is allowed by the standard model and has been measured in numerous experiments. In this Letter, we report a measurement of 2νββ decay half-life of ^{100}Mo to the ground state of ^{100}Ru of [7.07±0.02(stat)±0.11(syst)]×10^{18} yr by the CUPID-Mo experiment. With a relative precision of ±1.6% this is the most precise measurement to date of a 2νββ decay rate in ^{100}Mo. In addition, we constrain higher-order corrections to the spectral shape, which provides complementary nuclear structure information. We report a novel measurement of the shape factor ξ_{3,1}=0.45±0.03(stat)±0.05(syst) based on a constraint on the ratio of higher-order terms from theory, which can be reliably calculated. This is compared to theoretical predictions for different nuclear models. We also extract the first value for the effective axial vector coupling constant obtained from a spectral shape study of 2νββ decay.

Center for Theoretical Physics Sloane Physics Laboratory Yale University New Haven Connecticut 06520 8120 USA

Department of Modern Physics University of Science and Technology of China Hefei 230027 People's Republic of China

Department of Physics University of Jyväskylä P O Box 35 FI 40014 Jyväskylä Finland

Dipartimento di Fisica Sapienza Università di Roma Piazzale Aldo Moro 2 1 00185 Rome Italy

Dipartimento di Fisica Università di Milano Bicocca 1 20126 Milano Italy

Faculty of Mathematics Physics and Informatics Comenius University in Bratislava 842 48 Bratislava Slovakia

Finnish Institute for Educational Research University of Jyväskylä P O Box 35 FI 40014 Jyvaäskylä Finland

INFN Gran Sasso Science Institute 1 67100 L'Aquila Italy

INFN Laboratori Nazionali del Gran Sasso 1 67100 Assergi Italy

INFN Sezione di Milano Bicocca 1 20126 Milano Italy

INFN Sezione di Roma P le Aldo Moro 2 1 00185 Rome Italy

INFN Sezione di Roma Tor Vergata Via della Ricerca Scientifica 1 1 00133 Rome Italy

Institute for Nuclear Research of NASU 03028 Kyiv Ukraine

Institute of Experimental and Applied Physics Czech Technical University Prague 128 00 Prague Czech Republic

IRFU CEA Université Paris Saclay F 91191 Gif sur Yvette France

John de Laeter Centre for Isotope Research GPO Box U 1987 Curtin University Bentley Western Australia Australia

Karlsruhe Institute of Technology Institute for Astroparticle Physics 76021 Karlsruhe Germany

Karlsruhe Institute of Technology Institute for Data Processing and Electronics 76021 Karlsruhe Germany

Key Laboratory of Nuclear Physics and Ion beam Application Fudan University Shanghai 200433 People's Republic of China

Laboratory of Nuclear Problems JINR 141980 Dubna Moscow region Russia

Lawrence Berkeley National Laboratory Berkeley California 94720 USA

LSM Laboratoire Souterrain de Modane 73500 Modane France

Massachusetts Institute of Technology Cambridge Massachusetts 02139 USA

National Research Centre Kurchatov Institute Institute of Theoretical and Experimental Physics 117218 Moscow Russia

National Research Centre Kurchatov Institute Kurchatov Complex of Theoretical and Experimental Physics 117218 Moscow Russia

Nikolaev Institute of Inorganic Chemistry 630090 Novosibirsk Russia

Physik Department Technische Universität München Garching D 85748 Germany

Univ Lyon Université Lyon 1 CNRS IN2P3 IP2I Lyon F 69622 Villeurbanne France

Université Grenoble Alpes CNRS Grenoble INP SIMAP 38420 Saint Martin d'Hères France

Université Paris Saclay CNRS IN2P3 IJCLab 91405 Orsay France

University of California Berkeley California 94720 USA

References provided by Crossref.org