arXiv subjects

K. Hata

Publications and source records attributed to K. Hata.

22 records · Page 2Linked to original sources

arXiv2021

The nylon balloon for xenon loaded liquid scintillator in KamLAND-Zen 800 neutrinoless double-beta decay search experiment

The KamLAND-Zen 800 experiment is searching for the neutrinoless double-beta decay of $^{136}$Xe by using $^{136}$Xe-loaded liquid scintillator. The liquid scintillator is enclosed inside a balloon made of thin, transparent, low-radioactivity film that we call Inner Balloon (IB). The IB, apart from guaranteeing the liquid containment, also allows to minimize the background from cosmogenic muon-spallation products and $^{8}$B solar neutrinos. Indeed these events could contribute to the total counts in the region of interest around the Q-value of the double-beta decay of $^{136}$Xe. In this paper, we present an overview of the IB and describe the various steps of its commissioning minimizing the radioactive contaminations, from the material selection, to the fabrication of the balloon and its installation inside the KamLAND detector. Finally, we show the impact of the IB on the KamLAND background as measured by the KamLAND detector itself.

physics.ins-det↗

arXiv2021

Development of highly radiopure NaI(Tl) scintillator for PICOLON dark matter search project

The highly radiopure NaI(Tl) was developed to search for particle candidates of dark matter. The optimized methods were combined to reduce various radioactive impurities. The $^{40}$K was effectively reduced by the re-crystallization method. The progenies of the decay chains of uranium and thorium were reduced by appropriate resins. The concentration of natural potassium in NaI(Tl) crystal was reduced down to 20 ppb. Concentrations of alpha-ray emitters were successfully reduced by appropriate selection of resin. The present concentration of thorium series and 226Ra were $1.2 \pm1.4$ $μ$Bq/kg and $13\pm4$ $μ$Bq/kg, respectively. No significant excess in the concentration of $^{210}$Pb was obtained, and the upper limit was 5.7 $μ$Bq/kg at 90% C. L. The achieved level of radiopurity of NaI(Tl) crystals makes construction of a dark matter detector possible.

physics.ins-det↗

arXiv2021

A Search for Charged Excitation of Dark Matter with the KamLAND-Zen Detector

There are many theories where a dark matter particle is part of a multiplet with an electrically charged state. If WIMP dark matter ($χ^{0}$) is accompanied by a charged excited state ($χ^{-}$) separated by a small mass difference, it can form a stable bound state with a nucleus. In supersymmetric models, the $χ^{0}$ and the $χ^{-}$ could be the neutralino and a charged slepton, such as the neutralino-stau degenerate model. The formation binding process is expected to result in an energy deposition of {\it O}(1--10 MeV), making it suitable for detection in large liquid scintillator detectors. We describe new constraints on the bound state formation with a xenon nucleus using the KamLAND-Zen 400 Phase-II dataset. In order to enlarge the searchable parameter space, all xenon isotopes in the detector were used. For a benchmark parameter set of $m_{χ^{0}} = 100$ GeV and $Δm = 10$ MeV, this study sets the most stringent upper limits on the recombination cross section $\langleσv\rangle$ and the decay-width of $χ^{-}$ of $2.0 \times 10^{-31}$ ${\rm cm^3/s}$ and $1.1 \times 10^{-18}$ GeV, respectively (90\% confidence level).

hep-ex↗

arXiv2020

Search for Low-energy Electron Antineutrinos in KamLAND Associated with Gravitational Wave Events

We present the results of a search for MeV-scale electron antineutrino events in KamLAND in coincident with the 60 gravitational wave events/candidates reported by the LIGO/Virgo collaboration during their second and third observing runs. We find no significant coincident signals within a $\pm$ 500 s timing window from each gravitational wave and present 90% C.L. upper limits on the electron antineutrino fluence between $10^{8}$-$10^{13}\,{\mathrm cm^2}$ for neutrino energies in the energy range of 1.8-111 MeV.

astro-ph.HE↗