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Author

Ken-Ichi Fushimi

Other affiliations: Osaka University
Bio: Ken-Ichi Fushimi is an academic researcher from University of Tokushima. The author has contributed to research in topics: Neutrino & Double beta decay. The author has an hindex of 24, co-authored 158 publications receiving 2776 citations. Previous affiliations of Ken-Ichi Fushimi include Osaka University.


Papers
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Journal ArticleDOI
TL;DR: An improved search for neutrinoless double-beta (0νββ) decay of ^{136}Xe in the KamLAND-Zen experiment is presented and a significant reduction of the xenon-loaded liquid scintillator contaminant identified in previous searches is achieved.
Abstract: We present an improved search for neutrinoless double-beta (0νββ) decay of ^{136}Xe in the KamLAND-Zen experiment. Owing to purification of the xenon-loaded liquid scintillator, we achieved a significant reduction of the ^{110m}Ag contaminant identified in previous searches. Combining the results from the first and second phase, we obtain a lower limit for the 0νββ decay half-life of T_{1/2}^{0ν}>1.07×10^{26} yr at 90% C.L., an almost sixfold improvement over previous limits. Using commonly adopted nuclear matrix element calculations, the corresponding upper limits on the effective Majorana neutrino mass are in the range 61-165 meV. For the most optimistic nuclear matrix elements, this limit reaches the bottom of the quasidegenerate neutrino mass region.

1,055 citations

Journal ArticleDOI
TL;DR: This corrects the article DOI: 10.1103/PhysRevLett.117.082503 to reflect that the paper was originally published in Physical Review Letters, not RevLett, rather than Science.
Abstract: Author(s): Gando, A; Gando, Y; Hachiya, T; Hayashi, A; Hayashida, S; Ikeda, H; Inoue, K; Ishidoshiro, K; Karino, Y; Koga, M; Matsuda, S; Mitsui, T; Nakamura, K; Obara, S; Oura, T; Ozaki, H; Shimizu, I; Shirahata, Y; Shirai, J; Suzuki, A; Takai, T; Tamae, K; Teraoka, Y; Ueshima, K; Watanabe, H; Kozlov, A; Takemoto, Y; Yoshida, S; Fushimi, K; Banks, TI; Berger, BE; Fujikawa, BK; O'Donnell, T; Winslow, LA; Efremenko, Y; Karwowski, HJ; Markoff, DM; Tornow, W; Detwiler, JA; Enomoto, S; Decowski, MP; KamLAND-Zen Collaboration | Abstract: This corrects the article DOI: 10.1103/PhysRevLett.117.082503.

192 citations

Journal ArticleDOI
TL;DR: In this paper, 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 ), for the 0v ββ decay were obtained.

102 citations

Journal ArticleDOI
TL;DR: In this paper, a lower limit for the half-life of the neutrino-less double beta decay of 48 Ca was derived by a Monte Carlo simulation using the measured activities of 214 Bi and 220 Rn inside CaF 2 crystals.

67 citations

Journal ArticleDOI
TL;DR: The present Rapid Communication reports the first application of a huge scintillation detector to search for the nonbaryonic dark matter (DM) by investigating directly the elastic scattering of DM by ' I and Na nuclei in the NaI detector.
Abstract: Application of a large-volume NaI scintillator to search for the cold dark matter (DM) in the Universe is discussed A low-noise (-5 keV) and low-background { — 5/keVkg day) were achieved even with a large (365 kg) NaI scintillator Light output efFiciencies for 'Na and ' I were measured as 04+02 and 005+002, in the recoil energy range of 5— 100 keV and 40— 300 keV, respectively NaI is shown to have merits of a large volume, large scattering cross sections for dark matter, and of 100% abundance of finite-spin nucleus, but to have the demerits of a small form factor due to the finite-size effect of ' 'I at the presently measured energy region PACS number(s): 2940Mc, 9535+ d, 3450Bw, 1480Ly The present Rapid Communication reports the first application of a huge scintillation detector to search for the nonbaryonic dark matter (DM) by investigating directly the elastic scattering of DM by ' I and Na nuclei in the NaI detector Experimentally, DM candidates like heavy neutrino or neutral supersymmetric particles are able to be directly investigated by recoil nuclei scattered off in a detector [1] The expected density of these candidates near the Earth is as much as 03 GeV/crn, assuming that they are the major component of DM As their average velocity relative to the motion of the Earth is as slow as v/c — 10, the expected recoil energy (Ett ) of the nucleus which is scattered off by DM is of the order of a few keV to 100 keV, depending on the scattering angle and the DM mass The cross section of DM-nucleus scattering, if we assume DM to be neutrinos, is given in terms of the vector (g~) and the axial vector coupling (g„) constants, and it is proportional to the square of gv and/or g~ g~ and g„ are written as

59 citations


Cited by
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Journal Article
TL;DR: The first direct detection of gravitational waves and the first observation of a binary black hole merger were reported in this paper, with a false alarm rate estimated to be less than 1 event per 203,000 years, equivalent to a significance greater than 5.1σ.
Abstract: On September 14, 2015 at 09:50:45 UTC the two detectors of the Laser Interferometer Gravitational-Wave Observatory simultaneously observed a transient gravitational-wave signal. The signal sweeps upwards in frequency from 35 to 250 Hz with a peak gravitational-wave strain of 1.0×10(-21). It matches the waveform predicted by general relativity for the inspiral and merger of a pair of black holes and the ringdown of the resulting single black hole. The signal was observed with a matched-filter signal-to-noise ratio of 24 and a false alarm rate estimated to be less than 1 event per 203,000 years, equivalent to a significance greater than 5.1σ. The source lies at a luminosity distance of 410(-180)(+160) Mpc corresponding to a redshift z=0.09(-0.04)(+0.03). In the source frame, the initial black hole masses are 36(-4)(+5)M⊙ and 29(-4)(+4)M⊙, and the final black hole mass is 62(-4)(+4)M⊙, with 3.0(-0.5)(+0.5)M⊙c(2) radiated in gravitational waves. All uncertainties define 90% credible intervals. These observations demonstrate the existence of binary stellar-mass black hole systems. This is the first direct detection of gravitational waves and the first observation of a binary black hole merger.

4,375 citations

Journal ArticleDOI
TL;DR: In this article, the neutralino is considered as a superpartner in many supersymmetric theories, and the cosmological abundance of neutralino and the event rates for both direct and indirect detection schemes are discussed.
Abstract: There is almost universal agreement among astronomers that most of the mass in the Universe and most of the mass in the Galactic halo is dark. Many lines of reasoning suggest that the dark matter consists of some new, as yet undiscovered, weakly-interacting massive particle (WIMP). There is now a vast experimental effort being surmounted to detect WIMPS in the halo. The most promising techniques involve direct detection in low-background laboratory detectors and indirect detection through observation of energetic neutrinos from annihilation of WIMPs that have accumulated in the Sun and/or the Earth. Of the many WIMP candidates, perhaps the best motivated and certainly the most theoretically developed is the neutralino, the lightest superpartner in many supersymmetric theories. We review the minimal supersymmetric extension of the Standard Model and discuss prospects for detection of neutralino dark matter. We review in detail how to calculate the cosmological abundance of the neutralino and the event rates for both direct- and indirect-detection schemes, and we discuss astrophysical and laboratory constraints on supersymmetric models. We isolate and clarify the uncertainties from particle physics, nuclear physics, and astrophysics that enter at each step in the calculation. We briefly review other related dark-matter candidates and detection techniques.

2,047 citations

Journal ArticleDOI
TL;DR: In this article, the neutralino is proposed as the lightest superpartner in many supersymmetric theories, and it is shown how to calculate the cosmological abundance of neutralino and event rates for both direct and indirect detection schemes.

1,670 citations

01 Apr 2003
TL;DR: In this paper, the authors measured the flux of neutrino from distant nuclear reactors and found fewer nu;(e) events than expected from standard assumptions about nu; (e) propagation at the 99.95% C.L.yr exposure.
Abstract: KamLAND has measured the flux of nu;(e)'s from distant nuclear reactors. We find fewer nu;(e) events than expected from standard assumptions about nu;(e) propagation at the 99.95% C.L. In a 162 ton.yr exposure the ratio of the observed inverse beta-decay events to the expected number without nu;(e) disappearance is 0.611+/-0.085(stat)+/-0.041(syst) for nu;(e) energies >3.4 MeV. In the context of two-flavor neutrino oscillations with CPT invariance, all solutions to the solar neutrino problem except for the "large mixing angle" region are excluded.

1,659 citations