New search for double electron capture in 106 Cd decay with the TGV-2 spectrometer
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Experiment
New Search for Double Electron Capture in with the TGV-2 Spectrometer
106
Cd Decay
Ch. Briancon ¸ 1) , V. B. Brudanin2) , V. G. Egorov2), J. M. Jose3) , A. A. Klimenko2) , A. Kovalik2), S. V. Rosov2) , E. N. Rukhadze3) , N. I. Rukhadze2)* , 2) ˇ A. V. Salamatin2), V. V. Timkin2) , L. Fajt3) , R. Hodak3) , F. Simkovic , 2) 3) 3) 2) ˇ ˇ Yu. A. Shitov , M. Spavorova , I. Stekl , and E. A. Yakushev Received January 19, 2015; in final form, April 3, 2015
Abstract—A new experiment devoted to searches for double electron capture in 106 Cd decay is being performed at the Modane underground laboratory (4800 mwe) with the 32-detector TGV-2 spectrometer. The limit T1/2 (2νEC/EC) > 2.0 × 1020 yr at a 90% confidence level (C.L.) was obtained from a preliminary analysis of data obtained over 2250 h of measurements with about 23.2 g sample enriched in the isotope 106 Cd to 99.57%. The limits T1/2 (KL, 2741 keV) > 0.9 × 1020 yr and T1/2 (KK, 2718 keV) 1.4 × 1020 yr at a 90% C.L. on the neutrinoless decay of 106 Cd were obtained from measurements performed with the Obelix low-background spectrometer from high-purity germanium (HPGe spectrometer) for a sample of mass about 23.2 g enriched in the isotope 106 Cd. DOI: 10.1134/S1063778815060058
1. INTRODUCTION Investigation of double-beta decay (β − β − , β + β + , β + EC, and EC/EC processes) is of great importance for particle and nuclear physics as a sensitive tool for studying the properties of neutrinos and weak interaction. Neutrinoless double-beta decay has not yet been detected experimentally. An observation of 0νβ − β − decay of 76 Ge was declared by some members of the Heideberg–Moscow Collaboration [1], but this result was not recognized by the scientific community and was disproved by other members of this collaboration [2]. Two-neutrino (2νβ − β − ) decay was detected in a number of experiments for 11 nuclei: 48 Ca, 76 Ge, 82 Se, 96 Zr, 100 Mo, 116 Cd, 128 Te, 130 Te, 136 Xe, 150 Nd, and 238 U [3]. In recent years, there was a considerable growth of interest in other forms of double-beta decay—in particular, in EC/EC capture. Studies of 2νEC/EC capture yielded two positive results—that for 130 Ba from geochemical experiments [4] and an indication of the observation of this 1)
´ ´ ´ Centre de Spectrometrie Nucleaire et de Spectrometrie de Masse, Orsay, France. 2) Joint Institute for Nuclear Research, ul. Joliot-Curie 6, Dubna, Moscow oblast, 141980 Russia. 3) Institute of Experimental and Applied Physics, Czech Technical University in Prague (CTU), Horska 3a/22, CZ-12800 Praha 2, Czech Republic. * E-mail: [email protected]
process in 78 Kr decay [5]. The TGV-2 Collaboration is one of the leaders in studying the EC/EC-capture process [6–8]. The TGV-2 experiment studies 106 Cd decay (QEC/EC = 2775.39 ± 0.10 keV), which is one of the most promising candidates for the discovery of twoneutrino double electron capture. According to theoretical estimations, the half-life with respect to this process ranges between 1 × 1020 and 5 × 1021 yr [9]. The best experimental
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