Showing papers by "Tsuyoshi Nakaya published in 2018"
Journal Article•
TL;DR: Hyper-Kamiokande as mentioned in this paper is the third generation water Cherenkov detector, which is being developed by an international collaboration as a leading worldwide experiment based in Japan and will be hosted in the Tochibora mine, about 295 km away from the J-PARC proton accelerator in Tokai, Japan.
Abstract: On the strength of a double Nobel prize winning experiment (Super)Kamiokande and an extremely successful long baseline neutrino programme, the third generation Water Cherenkov detector, Hyper-Kamiokande, is being developed by an international collaboration as a leading worldwide experiment based in Japan. The Hyper-Kamiokande detector will be hosted in the Tochibora mine, about 295 km away from the J-PARC proton accelerator research complex in Tokai, Japan. The currently existing accelerator will be steadily upgraded to reach a MW beam by the start of the experiment. A suite of near detectors will be vital to constrain the beam for neutrino oscillation measurements. A new cavern will be excavated at the Tochibora mine to host the detector. The experiment will be the largest underground water Cherenkov detector in the world and will be instrumented with new technology photosensors, faster and with higher quantum efficiency than the ones in Super-Kamiokande. The science that will be developed will be able to shape the future theoretical framework and generations of experiments. Hyper-Kamiokande will be able to measure with the highest precision the leptonic CP violation that could explain the baryon asymmetry in the Universe. The experiment also has a demonstrated excellent capability to search for proton decay, providing a significant improvement in discovery sensitivity over current searches for the proton lifetime. The atmospheric neutrinos will allow to determine the neutrino mass ordering and, together with the beam, able to precisely test the three-flavour neutrino oscillation paradigm and search for new phenomena. A strong astrophysical programme will be carried out at the experiment that will also allow to measure precisely solar neutrino oscillation.
274 citations
TL;DR: In this article, an analysis of atmospheric neutrino data from all four run periods of Super-Kamiokande optimized for the sensitivity of neutrinos to the mass hierarchy is presented.
Abstract: An analysis of atmospheric neutrino data from all four run periods of Super-Kamiokande optimized for
sensitivity to the neutrino mass hierarchy is presented. Confidence intervals for Δm2
32, sin2 θ23, sin2 θ13 and
δCP are presented for normal neutrino mass hierarchy and inverted neutrino mass hierarchy hypotheses,
based on atmospheric neutrino data alone. Additional constraints from reactor data on θ13 and from
published binned T2K data on muon neutrino disappearance and electron neutrino appearance are added to
the atmospheric neutrino fit to give enhanced constraints on the above parameters. Over the range of
parameters allowed at 90% confidence level, the normal mass hierarchy is favored by between 91.9% and
94.5% based on the combined Super-Kamiokande plus T2K result.
199 citations
TL;DR: The T2K experiment measures muon neutrino disappearance and electron neutRino appearance in accelerator-produced neutrinos and antineutrino beams and obtained 2σ confidence interval for the CP-violating phase, δ_{CP, does not include the CP -conserving cases (δ_{ CP}=0, π).
Abstract: The T2K experiment measures muon neutrino disappearance and electron neutrino appearance in accelerator-produced neutrino and antineutrino beams. With an exposure of $14.7(7.6)\times 10^{20}$ protons on target in neutrino (antineutrino) mode, 89 $
u_e$ candidates and 7 anti-$
u_e$ candidates were observed while 67.5 and 9.0 are expected for $\delta_{CP}=0$ and normal mass ordering. The obtained $2\sigma$ confidence interval for the $CP$ violating phase, $\delta_{CP}$, does not include the $CP$-conserving cases ($\delta_{CP}=0,\pi$). The best-fit values of other parameters are $\sin^2\theta_{23} = 0.526^{+0.032}_{-0.036}$ and $\Delta m^2_{32}=2.463\pm0.065\times10^{-3} \mathrm{eV}^2/c^4$.
196 citations
TL;DR: In this article, the authors conducted sensitivity studies on an alternative configuration of the Hyper-Kamiokande experiment by locating the 2nd HK detector in Korea at $\sim$1100$-\ $1300 km baseline.
Abstract: We have conducted sensitivity studies on an alternative configuration of the Hyper-Kamiokande experiment by locating the 2nd Hyper-Kamiokande detector in Korea at $\sim$1100$-\ $1300 km baseline. Having two detectors at different baselines improves sensitivity to leptonic CP violation, neutrino mass ordering as well as nonstandard neutrino interactions. There are several candidate sites in Korea with greater than 1 km high mountains ranged at an 1$-$3 degree off-axis angle. Thanks to larger overburden of the candidate sites in Korea, low energy physics, such as solar and supernova neutrino physics as well as dark matter search, is expected to be improved. In this paper sensitivity studies on the CP violation phase and neutrino mass ordering are performed using current T2K systematic uncertainties in most cases. We plan to improve our sensitivity studies in the near future with better estimation of our systematic uncertainties.
95 citations
TL;DR: In this article, measurements of final-state proton multiplicity, muon and proton kinematics, and their correlations in charged-current pionless neutrino interactions, measured by the T2K ND280 near detector in its plastic scintillator (C8H8) target.
Abstract: This paper reports measurements of final-state proton multiplicity, muon and proton kinematics, and their correlations in charged-current pionless neutrino interactions, measured by the T2K ND280 near detector in its plastic scintillator (C8H8) target. The data were taken between years 2010 and 2013, corresponding to approximately 6×1020 protons on target. Thanks to their exploration of the proton kinematics and of imbalances between the proton and muon kinematics, the results offer a novel probe of the nuclear-medium effects most pertinent to the (sub-)GeV neutrino-nucleus interactions that are used in accelerator-based long-baseline neutrino oscillation measurements. These results are compared to many neutrino-nucleus interaction models which all fail to describe at least part of the observed phase space. In case of events without a proton above a detection threshold in the final state, a fully consistent implementation of the local Fermi gas model with multinucleon interactions gives the best description of the data. In the case of at least one proton in the final state, the spectral function model agrees well with the data, most notably when measuring the kinematic imbalance between the muon and the proton in the plane transverse to the incoming neutrino. Within the models considered, only the existence of multinucleon interactions are able to describe the extracted cross section within regions of high transverse kinematic imbalance. The effect of final-state interactions is also discussed.
81 citations
TL;DR: This is the first experimental search for boosted dark matter from the Galactic center or the Sun interacting in a terrestrial detector, and limits on boosted dark Matter event rates in multiple angular cones around the Galactic Center and Sun are calculated.
Abstract: A search for boosted dark matter using 161.9 kt yr of Super-Kamiokande IV data is presented. We search for an excess of elastically scattered electrons above the atmospheric neutrino background, with a visible energy between 100 MeV and 1 TeV, pointing back to the Galactic center or the Sun. No such excess is observed. Limits on boosted dark matter event rates in multiple angular cones around the Galactic center and Sun are calculated. Limits are also calculated for a baseline model of boosted dark matter produced from cold dark matter annihilation or decay. This is the first experimental search for boosted dark matter from the Galactic center or the Sun interacting in a terrestrial detector.
62 citations
TL;DR: In this article, a search for atmospheric tau neutrino appearance has been performed in the Super-Kamiokande experiment, and the result is consistent with the Standard Model prediction, agreeing to within 1.5σ.
Abstract: Using 5326 days of atmospheric neutrino data, a search for atmospheric tau neutrino appearance has been performed in the Super-Kamiokande experiment. Super-Kamiokande measures the tau normalization to be 1.47±0.32 under the assumption of normal neutrino hierarchy, relative to the expectation of unity with neutrino oscillation. The result excludes the hypothesis of no-tau appearance with a significance level of 4.6σ. The inclusive charged-current tau neutrino cross section averaged by the tau neutrino flux at Super-Kamiokande is measured to be (0.94±0.20)×10-38 cm2. The measurement is consistent with the Standard Model prediction, agreeing to within 1.5σ.
51 citations
TL;DR: In this article, the first differential measurement of the charged-current interaction cross section of νμ on water with no pions in the final state was made using the T2K experiment's off-axis near detector, and reported in doubly differential bins of muon momentum and angle.
Abstract: This paper reports the first differential measurement of the charged-current interaction cross section of νμ on water with no pions in the final state. This flux-averaged measurement has been made using the T2K experiment’s off-axis near detector, and is reported in doubly differential bins of muon momentum and angle. The flux-averaged total cross section in a restricted region of phase space was found to be σ=(0.95±0.08(stat)±0.06(det syst)±0.04(model syst)±0.08(flux))×10−38 cm2/n.
31 citations
TL;DR: In this article, the authors acknowledge the support of MEXT, Japan;============NSERC (Grant No. SAPPJ-2014-00031), NRC and CFI,======Canada; CEA and CNRS/IN2P3, France; DFG, Germany;======INFN, Italy; National Science Centre (NCN) and Ministry of Science and Higher Education, Poland; RSF, RFBR, and======Ministry of Education and Science, Russia; SNSF and======SERI, Switzerland; STFC, UK; and
Abstract: We thank the J-PARC staff for superb accelerator
performance. We thank the CERN NA61/SHINE
Collaboration for providing valuable particle production
data. We acknowledge the support of MEXT, Japan;
NSERC (Grant No. SAPPJ-2014-00031), NRC and CFI,
Canada; CEA and CNRS/IN2P3, France; DFG, Germany;
INFN, Italy; National Science Centre (NCN) and Ministry
of Science and Higher Education, Poland; RSF, RFBR, and
Ministry of Education and Science, Russia; MINECO and
European Regional Development Fund, Spain; SNSF and
SERI, Switzerland; STFC, UK; and DOE, U.S. We also
thank CERN for the UA1/NOMAD magnet, DESY for the
HERA-B magnet mover system, NII for SINET4, the
WestGrid and SciNet consortia in Compute Canada, and
GridPP in the United Kingdom. In addition, participation of
individual researchers and institutions has been further
supported by funds from ERC (FP7), H2020 Grant
No. RISE-GA644294-JENNIFER, European Union;
JSPS, Japan; Royal Society, United Kingdom; and the
Alfred P. Sloan Foundation and the DOE Early Career
program, U.S.
22 citations
TL;DR: In this paper, the results of a neutrino search in Super-Kamiokande (SK) for coincident signals with the first detected gravitational wave (GW) produced by a binary neutron-star merger, GW170817, which was followed by a short gamma-ray burst and a kilonova/macronova, were reported.
Abstract: We report the results of a neutrino search in Super-Kamiokande (SK) for coincident signals with the first detected gravitational wave (GW) produced by a binary neutron-star merger, GW170817, which was followed by a short gamma-ray burst, GRB170817A, and a kilonova/macronova. We searched for coincident neutrino events in the range from 3.5 MeV to ~100 PeV, in a time window ±500 s around the gravitational wave detection time, as well as during a 14-day period after the detection. No significant neutrino signal was observed for either time window. We calculated 90% confidence level upper limits on the neutrino fluence for GW170817. From the upward-going-muon events in the energy region above 1.6 GeV, the neutrino fluence limit is ${16.0}_{-0.6}^{+0.7}$ (${21.3}_{-0.8}^{+1.1}$) cm−2 for muon neutrinos (muon antineutrinos), with an error range of ±5° around the zenith angle of NGC4993, and the energy spectrum is under the assumption of an index of −2. The fluence limit for neutrino energies less than 100 MeV, for which the emission mechanism would be different than for higher-energy neutrinos, is also calculated. It is 6.6 × 107 cm−2 for anti-electron neutrinos under the assumption of a Fermi–Dirac spectrum with average energy of 20 MeV.
21 citations
TL;DR: In this article, the results of a neutrino search in Super-Kamiokande for coincident signals with the first detected gravitational wave produced by a binary neutron star merger, GW170817, was reported.
Abstract: We report the results of a neutrino search in Super-Kamiokande for coincident signals with the first detected gravitational wave produced by a binary neutron star merger, GW170817, which was followed by a short gamma-ray burst, GRB170817A, and a kilonova/macronova. We searched for coincident neutrino events in the range from 3.5 MeV to $\sim$100 PeV, in a time window $\pm$500 seconds around the gravitational wave detection time, as well as during a 14-day period after the detection. No significant neutrino signal was observed for either time window. We calculated 90% confidence level upper limits on the neutrino fluence for GW170817. From the upward-going-muon events in the energy region above 1.6 GeV, the neutrino fluence limit is $16.0^{+0.7}_{-0.6}$ ($21.3^{+1.1}_{-0.8}$) cm$^{-2}$ for muon neutrinos (muon antineutrinos), with an error range of $\pm5^{\circ}$ around the zenith angle of NGC4993, and the energy spectrum is under the assumption of an index of $-2$. The fluence limit for neutrino energies less than 100 MeV, for which the emission mechanism would be different than for higher-energy neutrinos, is also calculated. It is $6.6 \times 10^7$ cm$^{-2}$ for anti-electron neutrinos under the assumption of a Fermi-Dirac spectrum with average energy of 20 MeV.
Posted Content•
TL;DR: In this paper, the Super-Kamiokande detector was used to search for 10 dinucleon and nucleon decay modes that have a two-body final state with no hadrons.
Abstract: Using 0.37 megaton$\cdot$years of exposure from the Super-Kamiokande detector, we search for 10 dinucleon and nucleon decay modes that have a two-body final state with no hadrons. These baryon and lepton number violating modes have the potential to probe theories of unification and baryogenesis. For five of these modes the searches are novel, and for the other five modes we improve the limits by more than one order of magnitude. No significant evidence for dinucleon or nucleon decay is observed and we set lower limits on the partial lifetime of oxygen nuclei and on the nucleon partial lifetime that are above $4\times 10^{33}$ years for oxygen via the dinucleon decay modes and up to about $4 \times 10^{34}$ years for nucleons via the single nucleon decay modes.
TL;DR: In this article, the single π 0 production rate in neutral current neutrino interactions on water was measured using the POD, one of the subdetectors of the T2K near detector.
Abstract: The single π0 production rate in neutral current neutrino interactions on water in a neutrino beam with a peak neutrino energy of 0.6 GeV has been measured using the POD, one of the subdetectors of the T2K near detector. The production rate was measured for data taking periods when the POD contained water (2.64×1020 protons-on-target) and also periods without water (3.49×1020 protons-on-target). A measurement of the neutral current single π0 production rate on water is made using appropriate subtraction of the production rate with water in from the rate with water out of the target region. The subtraction analysis yields 106±41±69 signal events where the uncertainties are statistical (stat.) and systematic (sys.) respectively. This is consistent with the prediction of 157 events from the nominal simulation. The measured to expected ratio is 0.68±0.26(stat)±0.44(sys)±0.12(flux). The nominal simulation uses a flux integrated cross section of 7.63×10−39 cm2 per nucleon with an average neutrino interaction energy of 1.3 GeV.
TL;DR: The angular dependence of columnar recombination in xenon (Xe) gas, if observed for low energy nuclear tracks, can be used for a direction-sensitive dark matter search as mentioned in this paper.
Abstract: The angular dependence of columnar recombination in xenon (Xe) gas, if observed for low energy nuclear tracks, can be used for a direction-sensitive dark matter search. We measured both scintillation and ionization yields to study columnar recombination for 5.4 MeV alpha particles in a high pressure gas detector filled with Xe gas at a pressure of 8 atm. Because the recombination photons are emitted several microseconds after de-excitation, the scintillation photons are separated into fast and slow components. While the fast component is not dependent on the track angle relative to the drift electric field, the slow component increases when the track is aligned with the electric field. This result indicates that the track angle relative to the electric field can be reconstructed from the scintillation time profile.
TL;DR: In this paper, the angular dependence of columnar recombination in xenon gas, if observed for low energy nuclear tracks, can be used for a direction-sensitive dark matter search.
Abstract: 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.
TL;DR: In this article, the authors describe the separation of gamma-rays from neutrons with the pulse shape information of the CsI(Tl) scintillator, using a fast neutron beam and several gamma-ray sources.
Abstract: Fast neutrons are a large background to measurements of gamma-rays emitted from excited nuclei, such that detectors which can efficiently distinguish between the two are essential. In this paper we describe the separation of gamma-rays from neutrons with the pulse shape information of the CsI(Tl) scintillator, using a fast neutron beam and several gamma-ray sources. We find that a figure of merit optimized for this separation takes on large and stable values (nearly 4) between 5 and 10 MeV of electron equivalent deposited energy, the region of most interest to the study of nuclear de-excitation gamma-rays. Accordingly this work demonstrates the ability of CsI(Tl) scintillators to reject neutron backgrounds to gamma-ray measurements at these energies.
17 Dec 2018
TL;DR: In this paper, the authors summarized the conclusions of the Neutrino Town Meeting held at CERN in October 2018 to review the neutrino field at large with the aim of defining a strategy for accelerator-based neutrinos physics in Europe.
Abstract: This document summarizes the conclusions of the Neutrino Town Meeting held at CERN in October 2018 to review the neutrino field at large with the aim of defining a strategy for accelerator-based neutrino physics in Europe. The importance of the field across its many complementary components is stressed. Recommendations are presented regarding the accelerator based neutrino physics, pertinent to the European Strategy for Particle Physics. We address in particular i) the role of CERN and its neutrino platform, ii) the importance of ancillary neutrino cross-section experiments, and iii) the capability of fixed target experiments as well as present and future high energy colliders to search for the possible manifestations of neutrino mass generation mechanisms.
Posted Content•
TL;DR: In this paper, the authors summarized the conclusions of the Neutrino Town Meeting held at CERN in October 2018 to review the neutrino field at large with the aim of defining a strategy for accelerator-based neutrinos physics in Europe.
Abstract: This document summarizes the conclusions of the Neutrino Town Meeting held at CERN in October 2018 to review the neutrino field at large with the aim of defining a strategy for accelerator-based neutrino physics in Europe. The importance of the field across its many complementary components is stressed. Recommendations are presented regarding the accelerator based neutrino physics, pertinent to the European Strategy for Particle Physics. We address in particular i) the role of CERN and its neutrino platform, ii) the importance of ancillary neutrino cross-section experiments, and iii) the capability of fixed target experiments as well as present and future high energy colliders to search for the possible manifestations of neutrino mass generation mechanisms.
TL;DR: In this article, the authors describe the separation of gamma-rays from neutrons with the pulse shape information of the CsI(Tl) scintillator, using a fast neutron beam and several gamma-ray sources.
Abstract: Fast neutrons are a large background to measurements of gamma-rays emitted from excited nuclei, such that detectors which can efficiently distinguish between the two are essential. In this paper we describe the separation of gamma-rays from neutrons with the pulse shape information of the CsI(Tl) scintillator, using a fast neutron beam and several gamma-ray sources. We find that a figure of merit optimized for this separation takes on large and stable values (nearly 4) between 5 and 10 MeV of electron equivalent deposited energy, the region of most interest to the study of nuclear de-excitation gamma-rays. Accordingly this work demonstrates the ability of CsI(Tl) scintillators to reject neutron backgrounds to gamma-ray measurements at these energies.