Showing papers by "Ken-Ichi Fushimi published in 2022"
TL;DR: The KamLAND-Zen experiment has provided stringent constraints on the neutrinoless double-beta (0νββ) decay half-life in this paper using a xenonloaded liquid scintillator.
Abstract: The KamLAND-Zen experiment has provided stringent constraints on the neutrinoless double-beta (0νββ) decay half-life in ^{136}Xe using a xenon-loaded liquid scintillator. We report an improved search using an upgraded detector with almost double the amount of xenon and an ultralow radioactivity container, corresponding to an exposure of 970 kg yr of ^{136}Xe. These new data provide valuable insight into backgrounds, especially from cosmic muon spallation of xenon, and have required the use of novel background rejection techniques. We obtain a lower limit for the 0νββ decay half-life of T_{1/2}^{0ν}>2.3×10^{26} yr at 90% C.L., corresponding to upper limits on the effective Majorana neutrino mass of 36-156 meV using commonly adopted nuclear matrix element calculations.
52 citations
DOI•
TL;DR: In this article , the Kamioka Liquid-Scintillator Antineutrino Detector (KamLAND) was used to detect the geoneutrinos produced by the radioactive decays of uranium and thorium.
Abstract: The decay of the primordial isotopes 238U, 235U, 232Th, and 40K has contributed to the terrestrial heat budget throughout the Earth's history. Hence, the individual abundance of those isotopes are key parameters in reconstructing contemporary Earth models. The geoneutrinos produced by the radioactive decays of uranium and thorium have been observed with the Kamioka Liquid‐Scintillator Antineutrino Detector (KamLAND). Those measurements have been improved with more than 18‐year observation time, and improvement in detector background levels mainly with an 8‐year nearly reactor‐free period, which now permit spectroscopy with geoneutrinos. Our results yield the first constraint on both uranium and thorium heat contributions. The KamLAND result is consistent with geochemical estimations based on elemental abundances of chondritic meteorites and mantle peridotites. The High‐Q model is disfavored at 99.76% C.L. and a fully radiogenic model is excluded at 5.2σ assuming a homogeneous heat producing element distribution in the mantle.
4 citations
TL;DR: In this paper , the results of a time-coincident event search for low-energy electron antineutrinos in the KamLAND detector with gamma-ray bursts (GRBs) from the Gamma-ray Coordinates Network and Fermi Gamma-Ray Burst Monitor are presented.
Abstract: We present the results of a time-coincident event search for low-energy electron antineutrinos in the KamLAND detector with gamma-ray bursts ( GRBs ) from the Gamma-ray Coordinates Network and Fermi Gamma-ray Burst Monitor. Using a variable coincidence time window of ± 500 s plus the duration of each GRB, no statistically signi fi cant excess above the background is observed. We place the world ’ s most stringent 90% con fi dence level upper limit on the electron antineutrino fl uence below 17.5 MeV. Assuming a Fermi – Dirac neutrino energy spectrum from the GRB source, we use the available redshift data to constrain the electron antineutrino luminosity and effective temperature
TL;DR: In this paper , a search for core-collapse supernova neutrinos was conducted using long-term KamLAND data from 2002 March 9 to 2020 April 25, with an energy range of 1.8-111 MeV.
Abstract: We present the results of a search for core-collapse supernova neutrinos, using long-term KamLAND data from 2002 March 9 to 2020 April 25. We focus on the electron antineutrinos emitted from supernovae in the energy range of 1.8–111 MeV. Supernovae will make a neutrino event cluster with the duration of ∼10 s in the KamLAND data. We find no neutrino clusters and give the upper limit on the supernova rate to be 0.15 yr−1 with a 90% confidence level. The detectable range, which corresponds to a >95% detection probability, is 40–59 kpc and 65–81 kpc for core-collapse supernovae and failed core-collapse supernovae, respectively. This paper proposes to convert the supernova rate obtained by the neutrino observation to the Galactic star formation rate. Assuming a modified Salpeter-type initial mass function, the upper limit on the Galactic star formation rate is <(17.5–22.7) M ⊙ yr−1 with a 90% confidence level.
TL;DR: In this paper , the results of a search for MeV-scale astrophysical neutrinos in KamLAND were presented as an excess in the number of coincident neutrino interactions associated with the publicly available high-energy neutrini datasets from the IceCube Neutrino Observatory.
28 Mar 2022
TL;DR: In this paper , the neutrino-less double beta decay (0$
u\beta\beta$) of $^{48}$Ca with the CANDLES III system, which consists of CaF$2}$(pure) scintillators.
Abstract: We have studied the neutrino-less double beta decay(0$
u\beta\beta$) of $^{48}$Ca with the CANDLES III system, which consists of CaF$_{2}$(pure) scintillators. The first result of $^{48}$Ca double beta decay with the CANDLES III system was obtained by using 130.4 days of data. In this measurement, we achieved a background free measurement and a low background condition of 10$^{-3}$ events/keV/yr/(kg of $^{\rm nat.}$Ca). The sensitivity of this measurement, however, was limited by the small amount of $^{48}$Ca. For a more sensitive measurement of $^{48}$Ca 0$
u\beta\beta$, we have developed new techniques for $^{48}$Ca enrichment and CaF$_{2}$ scintillating bolometer. In this paper, we will also show the current status of these techniques.
25 Nov 2022
TL;DR: In this article , the axial coupling constant of the neutral-current quasielastic (NCQE) interaction was measured using atmospheric neutrino data at KamLAND.
Abstract: We report a measurement of the strange axial coupling constant $g_A^s$ using atmospheric neutrino data at KamLAND. This constant is a component of the axial form factor of the neutral-current quasielastic (NCQE) interaction. The value of $g_A^s$ significantly changes the ratio of proton and neutron NCQE cross sections. KamLAND is suitable for measuring NCQE interactions as it can detect nucleon recoils with low-energy thresholds and measure neutron multiplicity with high efficiency. KamLAND data, including the information on neutron multiplicity associated with the NCQE interactions, makes it possible to measure $g_A^s$ with a suppressed dependence on the axial mass $M_A$, which has not yet been determined. For a comprehensive prediction of the neutron emission associated with neutrino interactions, we establish a simulation of particle emission via nuclear deexcitation of $^{12}$C, a process not considered in existing neutrino Monte Carlo event generators. Energy spectrum fitting for each neutron multiplicity gives $g_A^s =-0.14^{+0.25}_{-0.26}$, which is the most stringent limit obtained using NCQE interactions without $M_A$ constraints. The two-body current contribution considered in this analysis relies on a theoretically effective model and electron scattering experiments and requires future verification by direct measurements and future model improvement.