K. Fushimi

Double beta decays of 100Mo

Abstract Double beta (ββ) decays of 100Mo were studied by means of ELEGANTS V. A finite half-life of T 2v 1 2 =(1.15 +0.30 −0.20 )×10 19 yr (68% CL ) for 2νββ decay and the most stringent lower limit of T 0v 1 2 > 4.7 × 10 21 yr (68% CL ) on the half-life for the 0vββ decay were obtained. The observed T 2ν 1 2 indicates very severe cancellation of the components of the relevant nuclear matrix element.

Double Beta Decays of 116Cd

Double beta decays (ββ) from the 0 + ground state in 116 Cd to the 0 + ground state in 116 Sn were studied by means of ELEGANT V. A finite half-life for the two-neutrino ββ(2νββ) and an upper limit on the neutrinoless one (0νββ) were obtained as T 2ν 1/2 =2.6 +0.9 -0.5 ×10 19 y and T 0ν 1/2 >6.3×10 21 y (68% C.L.), respectively. The nuclear matrix element M 2ν ββ was deduced as 0.069±0.009 in units of ( m e c 2 ) -1 . This supports the universal quenching of the 2νββ rates in this mass region, which is consistent with that previously measured in 100 Mo.

Limits on neutrino-less double beta decay of 100Mo

Abstract Exclusive measurements of neutrino-less double beta decays (0νββ) of 100Mo were made by means of ELEGANT V. Most stringent lower limits on the half-lives for the ground-state transition were obtained for the 0νββ processes as T 1 2 0ν (m ν ) > 5.2 × 10 22 y , T 1 2 0ν (λ) > 3.9 × 10 22 y and T 1 2 0ν (η) > 5.1 × 10 22 y , for the mass term 〈mν〉, for the right-handed current terms of 〈λ〉 and 〈η〉, respectively, and as T 1 2 0νB > 5.4 × 10 21 y for the process (0νββB) followed by a Majoron (B). These limits lead to the upper limits of 〈mν〉

Limits on the annual modulation of WIMPs-nucleus scattering with large-volume NaI(Tl) scintillators

Abstract A search for cold dark matters has been carried out with the 662 kg NaI scintillator array of ELEGANT V at the Kamioka underground laboratory. The annual modulation of weakly interacting massive particles (WIMPs) energy spectra has been investigated. No significant modulations beyond statistical fluctuations were found. Stringent limits were obtained on masses and cross sections for both axial-vector coupled and vector coupled WIMPs.

Search for spin-coupled dark matter by studying the axial-vector excitation of nuclei

Abstract Axial-vector (spin) excitation of 127 I by inelastic scattering of dark matter (DM) was studied to search for spin-coupled DM. The inelastic process from 127 I has the advantages of a large cross-section, a large scintillation output and of a known nuclear matrix element. Stringent limits by direct measurements were obtained on the purely spin-coupled DM candidates.

Results from KamLAND-Zen

KamLAND-Zen reports on a preliminary search for neutrinoless double-beta decay with 136Xe based on 114.8 live-days after the purification of the xenon loaded liquid scintillator. In this data, the problematic 110mAg background peak identified in previous searches is reduced by more than a factor of 10. By combining the KamLAND-Zen pre- and post-purification data, we obtain a preliminary lower limit on the 0νββ decay half-life of T1/20ν>2.6×1025 yr at 90% C.L. The search sensitivity will be enhanced with additional low background data after the purification. Prospects for further improvements with future KamLAND-Zen upgrades are also presented.

Multilayer Scintillator Responses for Mo Observatory of Neutrino Experiment Studied Using a Prototype Detector MOON-1

An ensemble of multilayer scintillators is discussed as an option of the high-sensitivity detector MOON (Mo Observatory of Neutrinos) for spectroscopic measurements of neutrinoless double beta decays. A prototype detector MOON-1, which consists of 6-layer plastic scintillator plates, was built to study the photon responses of the MOON-type detector. The photon responses, i.e., the number of scintillation photons collected and the energy resolution, which are key elements for high-sensitivity experiments, are found to be 1835 � 30 photoelectrons for 976 keV electrons and � ¼ 2:9 � 0:1% (� E=E ¼ 6:8 � 0:3% in FWHM) at the Q�� � 3 MeV region, respectively. The multilayer plastic scintillator structure with high energy resolution as well as a good signal for the background suppression of � –� rays is crucial for the MOON-type detector to achieve inverted-hierarchy neutrino-mass sensitivity. It will also be useful for medical and other rare-decay experiments as well.

Search for double-beta decay of

Abstract A search for double-beta decays of 136Xe to excited states of 136Ba has been performed with the first phase data set of the KamLAND-Zen experiment. The 0 1 + , 2 1 + and 2 2 + transitions of 0 ν β β decay were evaluated in an exposure of 89.5 kg ⋅ yr of 136Xe, while the same transitions of 2 ν β β decay were evaluated in an exposure of 61.8 kg ⋅ yr . No excess over background was found for all decay modes. The lower half-life limits of the 2 1 + state transitions of 0 ν β β and 2 ν β β decay were improved to T 1 / 2 0 ν ( 0 + → 2 1 + ) > 2.6 × 10 25 yr and T 1 / 2 2 ν ( 0 + → 2 1 + ) > 4.6 × 10 23 yr (90% C.L.), respectively. We report on the first experimental lower half-life limits for the transitions to the 0 1 + state of 136Xe for 0 ν β β and 2 ν β β decay. They are T 1 / 2 0 ν ( 0 + → 0 1 + ) > 2.4 × 10 25 yr and T 1 / 2 2 ν ( 0 + → 0 1 + ) > 8.3 × 10 23 yr (90% C.L.). The transitions to the 2 2 + states are also evaluated for the first time to be T 1 / 2 0 ν ( 0 + → 2 2 + ) > 2.6 × 10 25 yr and T 1 / 2 2 ν ( 0 + → 2 2 + ) > 9.0 × 10 23 yr (90% C.L.). These results are compared to recent theoretical predictions.

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In the late stages of nuclear burning for massive stars (

Xe to excited states of

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