arXiv subjects

K. Ueshima

Publications and source records attributed to K. Ueshima.

At least 19 recordsLinked to original sources

arXiv2022

Search for the Majorana Nature of Neutrinos in the Inverted Mass Ordering Region with KamLAND-Zen

The KamLAND-Zen experiment has provided stringent constraints on the neutrinoless double-beta ($0\nu\beta\beta$) 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 $0\nu\beta\beta$ decay half-life of $T_{1/2}^{0\nu} > 2.3 \times 10^{26}$ 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.

hep-ex↗

arXiv2021

Limits on astrophysical antineutrinos with the KamLAND experiment

We report on a search for electron antineutrinos ($\bar{\nu}_e$) from astrophysical sources in the neutrino energy range 8.3 to 30.8 MeV with the KamLAND detector. In an exposure of 6.72 kton-year of the liquid scintillator, we observe 18 candidate events via the inverse beta decay reaction. Although there is a large background uncertainty from neutral current atmospheric neutrino interactions, we find no significant excess over background model predictions. Assuming several supernova relic neutrino spectra, we give upper flux limits of 60--110 cm$^{-2}$ s$^{-1}$ (90% CL) in the analysis range and present a model-independent flux. We also set limits on the annihilation rates for light dark matter pairs to neutrino pairs. These data improves on the upper probability limit of $^{8}$B solar neutrinos converting into $\bar{\nu}_e$'s, $P_{\nu_e \rightarrow \bar{\nu}_e} < 3.5\times10^{-5}$ (90% CL) assuming an undistorted $\bar{\nu}_e$ shape. This corresponds to a solar $\bar{\nu}_e$ flux of 60 cm$^{-2}$ s$^{-1}$ (90% CL) in the analysis energy range.

astro-ph.HE↗

arXiv2021

Search for Solar Flare Neutrinos with the KamLAND detector

We report the result of a search for neutrinos in coincidence with solar flares from the GOES flare database. The search was performed on a 10.8 kton-year exposure of KamLAND collected from 2002 to 2019. This large exposure allows us to explore previously unconstrained parameter space for solar flare neutrinos. We found no statistical excess of neutrinos and established 90% confidence level upper limits of $8.4 \times 10^7$ cm$^{-2}$ ($3.0 \times 10^{9}$ cm$^{-2}$) on electron anti-neutrino (electron neutrino) fluence at 20 MeV normalized to the X12 flare, assuming that the neutrino fluence is proportional to the X-ray intensity.

astro-ph.SR↗

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

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 ($\chi^{0}$) is accompanied by a charged excited state ($\chi^{-}$) separated by a small mass difference, it can form a stable bound state with a nucleus. In supersymmetric models, the $\chi^{0}$ and the $\chi^{-}$ 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 $m_{\chi^{0}} = 100$ GeV and $\Delta m = 10$ MeV, this study sets the most stringent upper limits on the recombination cross section $\langle\sigma v\rangle$ and the decay-width of $\chi^{-}$ 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↗

arXiv2020

Design and performance of a high-pressure xenon gas TPC as a prototype for a large-scale neutrinoless double-beta decay search

A high-pressure xenon gas time projection chamber, with a unique cellular readout structure based on electroluminescence, has been developed for a large-scale neutrinoless double-beta decay search. In order to evaluate the detector performance and validate its design, a 180~L size prototype is being constructed and its commissioning with partial detector has been performed. The obtained energy resolution at 4.0~bar is 1.73 $\pm$ 0.07% (FWHM) at 511 keV. The energy resolution at the $^{136}$Xe neutrinoless double-beta decay Q-value is estimated to be between 0.79 and 1.52% (FWHM) by extrapolation. Reconstructed event topologies show patterns peculiar to track end-point which can be used to distinguish $0\nu\beta\beta$ signals from gamma-ray backgrounds.

physics.ins-det↗

arXiv2019

AXEL: High-pressure Xe gas TPC for BG-free $0\nu2\beta$ decay search

AXEL is a high-pressure xenon gas time projection chamber for neutrinoless double-beta decay (0n2b) search. The AXEL has a unique readout system called ELCC which has a cellular structure and photosensors to detect electroluminescence light produced by ionization electrons. We demonstrated the performance of the ELCC with a small prototype detector (AXEL-HP10L). The obtained energy resolution corresponds to 0.82 -- 1.74% (FWHM) at the 0n2b Q-value. We are constructing a new prototype (AXEL-HP180L) in order to study the energy resolution at the Q-value of 0n2b with a new design of ELCC with unit structure, newly developed electronics board, field-shaping electrodes, and Cockcroft-Walton-type high voltage power supply. For a future 1-ton scale large AXEL detector, we are developing new background-reduction techniques; topology identification with machine learning, positive-ion detection, and active-shield options.

physics.ins-det↗

arXiv2018

Angular dependence of columnar recombination in high pressure xenon gas using time profile of scintillation emission

The angular dependence of the columnar recombination in xenon gas, if observed for low energy nuclear tracks, can be used for a direction-sensitive dark matter search. We measured both scintillation and ionization to study columnar recombination for 5.4 MeV alpha particles in a high pressure gas detector filled with 8 atm xenon. Since the recombination photons are emitted several~$\mu$s after de-excitation emission, scintillation photons are separated to the fast and slow components. The fast component does not show dependence on the track angle relative to the drift electric field, on the other hand, the slow component increases when the track is aligned with the electric field. The result indicates that the track angle relative to the electric field can be reconstructed from the scintillation time profile.

astro-ph.IM↗

arXiv2017

Electroluminescence collection cell as a readout for a high energy resolution Xenon gas TPC

AXEL is a high pressure xenon gas TPC detector being developed for neutrinoless double-beta decay search. We use the proportional scintillation mode with a new electroluminescence light detection system to achieve high energy resolution in a large detector. The detector also has tracking capabilities, which enable significant background rejection. To demonstrate our detection technique, we constructed a 10L prototype detector filled with up to 10bar xenon gas. The FWHM energy resolution obtained by the prototype detector is 4.0 $\pm$ 0.30 $\%$ at 122 keV, which corresponds to 0.9 ~ 2.0 % when extrapolated to the Q value of the $0\nu\beta\beta$ decay of $^{136}$Xe.

physics.ins-det↗

arXiv2016

Search for electron antineutrinos associated with gravitational wave events GW150914 and GW151226 using KamLAND

We present a search for low energy antineutrino events coincident with the gravitational wave events GW150914 and GW151226, and the candidate event LVT151012 using KamLAND, a kiloton-scale antineutrino detector. We find no inverse beta-decay neutrino events within $\pm 500$ seconds of either gravitational wave signal. This non-detection is used to constrain the electron antineutrino fluence and the luminosity of the astrophysical sources.

astro-ph.HE↗

arXiv2015

Search for double-beta decay of 136Xe to excited states of 136Ba with the KamLAND-Zen experiment

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{\nu}\{beta}\{beta} decay were evaluated in an exposure of 89.5kg-yr of 136Xe, while the same transitions of 2{\nu}\{beta}\{beta} decay were evaluated in an exposure of 61.8kg-yr. No excess over background was found for all decay modes. The lower half-life limits of the 2+1 state transitions of 0{\nu}\{beta}\{beta} and 2{\nu}\{beta}\{beta} decay were improved to T(0{\nu}, 0+ \rightarrow 2+) > 2.6\times10^25 yr and T(2{\nu}, 0+ \rightarrow 2+) > 4.6\times10^23 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{\nu}\{beta}\{beta} and 2{\nu}\{beta}\{beta} decay. They are T (0{\nu}, 0+ \rightarrow 0+) > 2.4\times10^25 yr and T(2{\nu}, 0+ \rightarrow 0+) > 8.3\times10^23 yr (90% C.L.). The transitions to the 2+2 states are also evaluated for the first time to be T(0{\nu}, 0+ \rightarrow 2+) > 2.6\times10^25 yr and T(2{\nu}, 0+ \rightarrow 2+) > 9.0\times10^23 yr (90% C.L.). These results are compared to recent theoretical predictions.

hep-ex↗

arXiv2015

KamLAND Sensitivity to Neutrinos from Pre-Supernova Stars

In the late stages of nuclear burning for massive stars ($M>8~M_{\sun}$), the production of neutrino-antineutrino pairs through various processes becomes the dominant stellar cooling mechanism. As the star evolves, the energy of these neutrinos increases and in the days preceding the supernova a significant fraction of emitted electron anti-neutrinos exceeds the energy threshold for inverse beta decay on free hydrogen. This is the golden channel for liquid scintillator detectors because the coincidence signature allows for significant reductions in background signals. We find that the kiloton-scale liquid scintillator detector KamLAND can detect these pre-supernova neutrinos from a star with a mass of $25~M_{\sun}$ at a distance less than 690~pc with 3$\sigma$ significance before the supernova. This limit is dependent on the neutrino mass ordering and background levels. KamLAND takes data continuously and can provide a supernova alert to the community.

astro-ph.HE↗

arXiv2015

Study of electron anti-neutrinos associated with gamma-ray bursts using KamLAND

We search for electron anti-neutrinos ($\overline{\nu}_e$) from long and short-duration gamma-ray bursts~(GRBs) using data taken by the KamLAND detector from August 2002 to June 2013. No statistically significant excess over the background level is found. We place the tightest upper limits on $\overline{\nu}_e$ fluence from GRBs below 7 MeV and place first constraints on the relation between $\overline{\nu}_e$ luminosity and effective temperature.

astro-ph.HE↗

arXiv2014

A compact ultra-clean system for deploying radioactive sources inside the KamLAND detector

We describe a compact, ultra-clean device used to deploy radioactive sources along the vertical axis of the KamLAND liquid-scintillator neutrino detector for purposes of calibration. The device worked by paying out and reeling in precise lengths of a hanging, small-gauge wire rope (cable); an assortment of interchangeable radioactive sources could be attached to a weight at the end of the cable. All components exposed to the radiopure liquid scintillator were made of chemically compatible UHV-cleaned materials, primarily stainless steel, in order to avoid contaminating or degrading the scintillator. To prevent radon intrusion, the apparatus was enclosed in a hermetically sealed housing inside a glove box, and both volumes were regularly flushed with purified nitrogen gas. An infrared camera attached to the side of the housing permitted real-time visual monitoring of the cable's motion, and the system was controlled via a graphical user interface.

physics.ins-det↗

arXiv2014

7Be Solar Neutrino Measurement with KamLAND

We report a measurement of the neutrino-electron elastic scattering rate of 862 keV 7Be solar neutrinos based on a 165.4 kton-day exposure of KamLAND. The observed rate is 582 +/- 90 (kton-day)^-1, which corresponds to a 862 keV 7Be solar neutrino flux of (3.26 +/- 0.50) x 10^9 cm^-2s^-1, assuming a pure electron flavor flux. Comparing this flux with the standard solar model prediction and further assuming three flavor mixing, a nu_e survival probability of 0.66 +/- 0.14 is determined from the KamLAND data. Utilizing a global three flavor oscillation analysis, we obtain a total 7Be solar neutrino flux of (5.82 +/- 0.98) x 10^9 cm^-2s^-1, which is consistent with the standard solar model predictions.

hep-ex↗

arXiv2014

CeLAND: search for a 4th light neutrino state with a 3 PBq 144Ce-144Pr electron antineutrino generator in KamLAND

The reactor neutrino and gallium anomalies can be tested with a 3-4 PBq (75-100 kCi scale) 144Ce-144Pr antineutrino beta-source deployed at the center or next to a large low-background liquid scintillator detector. The antineutrino generator will be produced by the Russian reprocessing plant PA Mayak as early as 2014, transported to Japan, and deployed in the Kamioka Liquid Scintillator Anti-Neutrino Detector (KamLAND) as early as 2015. KamLAND's 13 m diameter target volume provides a suitable environment to measure the energy and position dependence of the detected neutrino flux. A characteristic oscillation pattern would be visible for a baseline of about 10 m or less, providing a very clean signal of neutrino disappearance into a yet-unknown, sterile neutrino state. This will provide a comprehensive test of the electron dissaperance neutrino anomalies and could lead to the discovery of a 4th neutrino state for Delta_m^2 > 0.1 eV^2 and sin^2(2theta) > 0.05.

physics.ins-det↗

arXiv2013

White paper: CeLAND - Investigation of the reactor antineutrino anomaly with an intense 144Ce-144Pr antineutrino source in KamLAND

We propose to test for short baseline neutrino oscillations, implied by the recent reevaluation of the reactor antineutrino flux and by anomalous results from the gallium solar neutrino detectors. The test will consist of producing a 75 kCi 144Ce - 144Pr antineutrino source to be deployed in the Kamioka Liquid Scintillator Anti-Neutrino Detector (KamLAND). KamLAND's 13m diameter target volume provides a suitable environment to measure energy and position dependence of the detected neutrino flux. A characteristic oscillation pattern would be visible for a baseline of about 10 m or less, providing a very clean signal of neutrino disappearance into a yet-unknown, "sterile" state. Such a measurement will be free of any reactor-related uncertainties. After 1.5 years of data taking the Reactor Antineutrino Anomaly parameter space will be tested at > 95% C.L.

hep-ex↗