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Register a new userNeutrino-less Double Beta Decay of 48Ca studied by CaF2(Eu) Scintillators
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We searched for the neutrino-less double beta decay(0nbb) of 48Ca by using CaF2(Eu) scintillators. Analysis of their pulse shapes was effective to reduce backgrounds. No events are observed in the Q-value region for the data of 3394 kg days. It gives a lower limit (90% confidence level) of T > 2.7 x 10^22 year for the half life of 0nbb of 48Ca. Combined with our previous data for 1553 kg days, we obtained more stringent limit of T > 5.8 x 10^22 year.
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Large-scale shell model calculations including two major shells are carried out, and the ingredients of nuclear matrix element for two-neutrino double beta decay are investigated. Based on the comparison between the shell model calculations accounting only for one major shell ($pf$-shell) and those for two major shells ($sdpf$-shell), the effect due to the excitation across the two major shells is quantitatively evaluated.
A new phase of 116Cd double beta decay experiment is in progress in the Solotvina Underground Laboratory. Four enriched 116CdWO4 scintillators with total mass 339 g are used in a set up, whose active shield is made of 15 natural CdWO4 crystals (20.6 kg). The background rate in the energy interval 2.5-3.2 MeV is 0.03 counts/y*kg*keV. The half-life for 2-neutrino 2-beta decay of 116Cd is measured as T{1/2}(2-neutrino) = [2.6+-0.1(stat)-0.4+0.7}(syst)]*10**19 y. The T{1/2} limits for neutrinoless 2-beta decay of 116Cd are set as T{1/2} >= 0.7(2.5)*10**23 y at 90%(68%) C.L. for transition to ground state of 116Sn, while for decays to the first 2+ and second 0+ excited levels of 116Sn as T{1/2}>=1.3(4.8)*10**22 y and >=0.7(2.4)*10**22 y with 90%(68%) C.L., respectively. For 0-neutrino 2-beta decay with emission of one or two Majorons, the limits are T{1/2}(0-neutrino M1) >=3.7(5.8)*10**21 y and T{1/2}(0-neutrino M2)>=5.9(9.4)*10**20 y at 90%(68%) C.L. Restrictions on the value of the neutrino mass, right-handed admixtures in the weak interaction, and the neutrino-Majoron coupling constant are derived as: m(neutrino)<=2.6(1.4) eV, eta <=3.9*10**-8, lambda <=3.4*10**-6, and g{M}<= 12(9.5)*10**-5 at 90%(68%) C.L., respectively.
CUPID-0 is the first pilot experiment of CUPID, a next-generation project searching for neutrino-less double beta decay. In its first scientific run, CUPID-0 operated 26 ZnSe cryogenic calorimeters coupled to light detectors in the underground Laboratori Nazionali del Gran Sasso. In this work, we analyzed a ZnSe exposure of 11.34 kg$times$yr to search for the neutrino-less double beta decay of $^{70}$Zn and for the neutrino-less positron-emitting electron capture of $^{64}$Zn. We found no evidence for these decays and set 90$%$ credible interval limits of ${rm T}_{1/2}^{0 ubetabeta}(^{70}{rm Zn}) > 1.6 times 10^{21}$ yr and ${rm T}_{1/2}^{0 u EC beta+}(^{64}{rm Zn}) > 1.2 times 10^{22}$ yr, surpassing by almost two orders of magnitude the previous experimental results
Energy resolution, alpha/beta ratio, pulse-shape discrimination for gamma rays and alpha particles, temperature dependence of scintillation properties, and radioactive contamination were studied with CaMoO4 crystal scintillators. A high sensitivity experiment to search for neutrinoless double beta decay of 100-Mo by using CaMoO4 scintillators is discussed.
PbWO4 crystal scintillators are discussed as an active shield and light-guides in 116Cd double beta decay experiment with CdWO4 scintillators. Scintillation properties and radioactive contamination of PbWO4 scintillators were investigated. Energy resolution of CdWO4 detector, coupled to PbWO4 crystal as a light-guide, was tested. Efficiency of PbWO4-based active shield to suppress background from the internal contamination of PbWO4 crystals was calculated. Using of lead tungstate crystal scintillators as high efficiency 4-pi active shield could allow to build sensitive double beta experiment with 116CdWO4 crystal scintillators.
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