H. Miyawaki

Scintillation efficiency of nuclear recoils in a CaF2(Eu) crystal for Dark Matter search

Abstract The scintillation efficiency (quenching factor) of fluorine and calcium nuclei recoiling in a CaF 2 (Eu) crystal was measured in an energy region relevant to Dark Matter searches. The recoiling nuclei were obtained via the 19 F(n,n′) and 40 Ca(n,n′) reactions, where the neutron beam was provided via the d(d,n) 3 He reaction. The quenching factor of F and Ca nuclei in the CaF 2 (Eu) crystal was found to be 11–20%, and 9–23% relative to the electron equivalent energy for 53–192xa0keV and 25–91xa0keV recoil energies, respectively, and the energy dependence was observed. The quenching factor we measured here is a little larger than that of previous studies, which may depend on the Eu doping concentration of the crystal.

Neutrino-less double-β decay of 48Ca studied by CaF2(Eu) scintillators

We searched for the neutrino-less double-β decay(0νββ) of 48 Ca by using CaF 2 (Eu) scintillators. Analysis of their pulse shapes was effective to reduce backgrounds. No events are observed in the Q ββ value region for the data of 3394 kg day. It gives a lower limit (90% confidence level) of T 0νββ ½ > 2.7 x 10 22 year for the half-life of 0νββ of 48 Ca. Combined with our previous data for 1553 kg day [I. Ogawa et al., Nucl. Phys. A730, 215 (2004)], we obtained a more stringent limit of T 0νββ ½ > 5.8 × 10 22 year.

Double beta decay study of 48Ca by CaF2 scintillator

Abstract A CaF 2 scintillation detector system (ELEGANT VI) is developed to search for neutrinoless double beta decay (0νDBD) of 48 Ca. No events were observed around the Q -value energy region after the analysis of 4.23 kg yr data. To derive the lower limit for the half-life, the expected number of background events was estimated by a Monte Carlo simulation using the measured activities of 214 Bi and 220 Rn inside CaF 2 crystals. A new lower limit is obtained to be 1.8 × 10 22 yr at the 90% C.L.

Double beta decays and ELEGANT V and VI at Oto Cosmo Observatory

Abstract Exclusive measurements of neutrino-less double beta decays(0νββ) of 100 Mo were made by means of ELEGANT V at Kamioka Underground Laboratory. Oto Cosmo Observatory has been constructed for underground laboratory for ELEGANT V and VI for the study of 0νββ of 100 Mo and 48 Ca, search for dark matters and so on.

Neutrino-less double-beta decay of Ca-48 studied by Ca F(2)(Eu) scintillators

We searched for the neutrino-less double-β decay(0νββ) of 48 Ca by using CaF 2 (Eu) scintillators. Analysis of their pulse shapes was effective to reduce backgrounds. No events are observed in the Q ββ value region for the data of 3394 kg day. It gives a lower limit (90% confidence level) of T 0νββ ½ > 2.7 x 10 22 year for the half-life of 0νββ of 48 Ca. Combined with our previous data for 1553 kg day [I. Ogawa et al., Nucl. Phys. A730, 215 (2004)], we obtained a more stringent limit of T 0νββ ½ > 5.8 × 10 22 year.

Neutrino-less double-βdecay ofCa48studied byCaF2(Eu) scintillators

We searched for the neutrino-less double-β decay(0νββ) of 48 Ca by using CaF 2 (Eu) scintillators. Analysis of their pulse shapes was effective to reduce backgrounds. No events are observed in the Q ββ value region for the data of 3394 kg day. It gives a lower limit (90% confidence level) of T 0νββ ½ > 2.7 x 10 22 year for the half-life of 0νββ of 48 Ca. Combined with our previous data for 1553 kg day [I. Ogawa et al., Nucl. Phys. A730, 215 (2004)], we obtained a more stringent limit of T 0νββ ½ > 5.8 × 10 22 year.

Neutrino-less double-{beta} decay of {sup 48}Ca studied by CaF{sub 2}(Eu) scintillators

We searched for the neutrino-less double-β decay(0νββ) of 48 Ca by using CaF 2 (Eu) scintillators. Analysis of their pulse shapes was effective to reduce backgrounds. No events are observed in the Q ββ value region for the data of 3394 kg day. It gives a lower limit (90% confidence level) of T 0νββ ½ > 2.7 x 10 22 year for the half-life of 0νββ of 48 Ca. Combined with our previous data for 1553 kg day [I. Ogawa et al., Nucl. Phys. A730, 215 (2004)], we obtained a more stringent limit of T 0νββ ½ > 5.8 × 10 22 year.

Double beta decay of 48Ca studied by CaF2(Eu) scintillators

We report the new limit on the half-life of neutrino-less double beta decay(0νββ) of 48Ca. In order to achieve the background free measurement, measurement of pulse shape was essential. We have observed no event in the Qββ-value region. We set the new limit on 0νββ half-life as T0νββ1/2 > 40 × 1022 year.