Showing papers by "K. Nishikawa published in 2011"
TL;DR: The T2K experiment observes indications of ν (μ) → ν(e) appearance in data accumulated with 1.43×10(20) protons on target, and under this hypothesis, the probability to observe six or more candidate events is 7×10(-3), equivalent to 2.5σ significance.
Abstract: The T2K experiment observes indications of nu(mu) -> nu(mu) e appearance in data accumulated with 1.43 x 10(20) protons on target. Six events pass all selection criteria at the far detector. In a three-flavor neutrino oscillation scenario with |Delta m(23)(2)| = 2.4 x 10(-3) eV(2), sin(2)2 theta(23) = 1 and sin(2)2 theta(13) = 0, the expected number of such events is 1.5 +/- 0.3(syst). Under this hypothesis, the probability to observe six or more candidate events is 7 x 10(-3), equivalent to 2.5 sigma significance. At 90% C.L., the data are consistent with 0.03(0.04) < sin(2)2 theta(13) < 0.28(0.34) for delta(CP) = 0 and a normal (inverted) hierarchy.
1,361 citations
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11 Dec 2011-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: The T2K experiment as discussed by the authors is a long-baseline neutrino oscillation experiment whose main goal is to measure the last unknown lepton sector mixing angle by observing its appearance in a particle beam generated by the J-PARC accelerator.
Abstract: The T2K experiment is a long-baseline neutrino oscillation experiment Its main goal is to measure the last unknown lepton sector mixing angle {\theta}_{13} by observing {
u}_e appearance in a {
u}_{\mu} beam It also aims to make a precision measurement of the known oscillation parameters, {\Delta}m^{2}_{23} and sin^{2} 2{\theta}_{23}, via {
u}_{\mu} disappearance studies Other goals of the experiment include various neutrino cross section measurements and sterile neutrino searches The experiment uses an intense proton beam generated by the J-PARC accelerator in Tokai, Japan, and is composed of a neutrino beamline, a near detector complex (ND280), and a far detector (Super-Kamiokande) located 295 km away from J-PARC This paper provides a comprehensive review of the instrumentation aspect of the T2K experiment and a summary of the vital information for each subsystem
714 citations
University of Tokyo1, Kyoto University2, University of California, Irvine3, Autonomous University of Madrid4, Boston University5, University of Wisconsin-Madison6, Brookhaven National Laboratory7, California State University, Dominguez Hills8, Chonnam National University9, Duke University10, Fukuoka Institute of Technology11, Gifu University12, Kanagawa University13, Kobe University14, Miyagi University of Education15, Nagoya University16, Stony Brook University17, Niigata University18, Okayama University19, Osaka University20, Seoul National University21, Shizuoka University22, Sungkyunkwan University23, Tokai University24, Tsinghua University25, University of Warsaw26, University of Washington27, University of Minnesota28
TL;DR: The results of the third phase of the Super-Kamiokande solar neutrino measurement are presented and compared to the first and second phase results in this article, where improved detector calibrations, a full detector simulation, and improved analysis methods are estimated to be approximately 2.1%, which is about two thirds of the systematic uncertainty for the first phase.
Abstract: The results of the third phase of the Super-Kamiokande solar neutrino measurement are presented and compared to the first and second phase results. With improved detector calibrations, a full detector simulation, and improved analysis methods, the systematic uncertainty on the total neutrino flux is estimated to be $\ifmmode\pm\else\textpm\fi{}2.1%$, which is about two thirds of the systematic uncertainty for the first phase of Super-Kamiokande. The observed $^{8}\mathrm{B}$ solar flux in the 5.0 to 20 MeV total electron energy region is $2.32\ifmmode\pm\else\textpm\fi{}0.04(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.05(\mathrm{sys})\ifmmode\times\else\texttimes\fi{}{10}^{6}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}2}\text{ }{\mathrm{sec}}^{\ensuremath{-}1}$ under the assumption of pure electron-flavor content, in agreement with previous measurements. A combined oscillation analysis is carried out using SK-I, II, and III data, and the results are also combined with the results of other solar neutrino experiments. The best-fit oscillation parameters are obtained to be ${sin }^{2}{\ensuremath{\theta}}_{12}={0.30}_{\ensuremath{-}0.01}^{+0.02}({tan }^{2}{\ensuremath{\theta}}_{12}={0.42}_{\ensuremath{-}0.02}^{+0.04})$ and $\ensuremath{\Delta}{m}_{21}^{2}={6.2}_{\ensuremath{-}1.9}^{+1.1}\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}\text{ }\text{ }{\mathrm{eV}}^{2}$. Combined with KamLAND results, the best-fit oscillation parameters are found to be ${sin }^{2}{\ensuremath{\theta}}_{12}=0.31\ifmmode\pm\else\textpm\fi{}0.01({tan }^{2}{\ensuremath{\theta}}_{12}=0.44\ifmmode\pm\else\textpm\fi{}0.03)$ and $\ensuremath{\Delta}{m}_{21}^{2}=7.6\ifmmode\pm\else\textpm\fi{}0.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}\text{ }\text{ }{\mathrm{eV}}^{2}$. The $^{8}\mathrm{B}$ neutrino flux obtained from global solar neutrino experiments is $5.3\ifmmode\pm\else\textpm\fi{}0.2(\mathrm{stat}+\mathrm{sys})\ifmmode\times\else\texttimes\fi{}{10}^{6}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}2}\text{ }{\mathrm{s}}^{\ensuremath{-}1}$, while the $^{8}\mathrm{B}$ flux becomes $5.1\ifmmode\pm\else\textpm\fi{}0.1(\mathrm{stat}+\mathrm{sys})\ifmmode\times\else\texttimes\fi{}{10}^{6}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}2}\text{ }{\mathrm{s}}^{\ensuremath{-}1}$ by adding KamLAND results. In a three-flavor analysis combining all solar neutrino experiments, the upper limit of ${sin }^{2}{\ensuremath{\theta}}_{13}$ is 0.060 at 95% C.L.. After combination with KamLAND results, the upper limit of ${sin }^{2}{\ensuremath{\theta}}_{13}$ is found to be 0.059 at 95% C.L.
404 citations
Nagoya University1, University of Tokyo2, Institute for the Physics and Mathematics of the Universe3, Boston University4, University of California, Irvine5, California State University, Dominguez Hills6, Chonnam National University7, Duke University8, Fukuoka Institute of Technology9, Gifu University10, University of Hawaii11, KEK12, Kobe University13, Kyoto University14, Miyagi University of Education15, State University of New York System16, Niigata University17, Okayama University18, Osaka University19, Seoul National University20, Shizuoka University21, Sungkyunkwan University22, Tokai University23, Tsinghua University24, University of Warsaw25, University of Washington26, University of Minnesota27
TL;DR: In this article, an indirect search for high energy neutrinos from Weakly Interacting Massive Particle (WIMP) annihilation in the Sun using upward-going muon (upmu) events at Super-Kamiokande was performed.
Abstract: We present the result of an indirect search for high energy neutrinos from Weakly Interacting Massive Particle (WIMP) annihilation in the Sun using upward-going muon (upmu) events at Super-Kamiokande. Data sets from SKI-SKIII (3109.6 days) were used for the analysis. We looked for an excess of neutrino signal from the Sun as compared with the expected atmospheric neutrino background in three upmu categories: stopping, non-showering, and showering. No significant excess was observed. The 90% C.L. upper limits of upmu flux induced by WIMPs of 100 GeV c-2 were 6.4 × 10–15 cm–2 s–1 and 4.0 × 10–15 cm–2 s–1 for the soft and hard annihilation channels, respectively. These limits correspond to upper limits of 4.5 × 10–39 cm–2 and 2.7 × 10–40 cm–2 for spin-dependent WIMP-nucleon scattering cross sections in the soft and hard annihilation channels, respectively.
189 citations
TL;DR: In this paper, an indirect search for high energy neutrinos from WIMP annihilation in the Sun using upward-going muon (upmu) events at Super-Kamiokande was performed.
Abstract: We present the result of an indirect search for high energy neutrinos from WIMP annihilation in the Sun using upward-going muon (upmu) events at Super-Kamiokande. Datasets from SKI-SKIII (3109.6 days) were used for the analysis. We looked for an excess of neutrino signal from the Sun as compared with the expected atmospheric neutrino background in three upmu categories: stopping, non-showering, and showering. No significant excess was observed. The 90% C.L. upper limits of upward-going muon flux induced by WIMPs of 100 GeV/c$^2$ were 6.4$\times10^{-15}$ cm$^{-2}$ sec$^{-1}$ and 4.0$\times10^{-15}$ cm$^{-2}$ sec$^{-1}$ for the soft and hard annihilation channels, respectively. These limits correspond to upper limits of 4.5$\times10^{-39}$ cm$^{-2}$ and 2.7$\times10^{-40}$ cm$^{-2}$ for spin-dependent WIMP-nucleon scattering cross sections in the soft and hard annihilation channels, respectively.
176 citations
University of Geneva1, University of Warsaw2, National and Kapodistrian University of Athens3, Saint Petersburg State University4, Joint Institute for Nuclear Research5, Karlsruhe Institute of Technology6, Warsaw University of Technology7, Hungarian Academy of Sciences8, Federico Santa María Technical University9, Jagiellonian University10, University of Silesia in Katowice11, Pusan National University12, Stony Brook University13, ETH Zurich14, University of Bern15, Eötvös Loránd University16, Jan Kochanowski University17, Frankfurt University of Applied Sciences18, University of Wrocław19, Sofia University20, Goethe University Frankfurt21, University of Bergen22
TL;DR: In this article, the neutrino interaction cross sections and charged pion spectra were measured with the large-acceptance NA61/SHINE spectrometer at the CERN SPS.
Abstract: Interaction cross sections and charged pion spectra in p+C interactions at 31 GeV/c were measured with the large-acceptance NA61/SHINE spectrometer at the CERN SPS. These data are required to improve predictions of the neutrino flux for the T2K long-baseline neutrino oscillation experiment in Japan. A set of data collected during the first NA61/SHINE run in 2007 with an isotropic graphite target with a thickness of 4% of a nuclear interaction length was used for the analysis. The measured p+C inelastic and production cross sections are 257.2 {+-} 1.9 {+-} 8.9 and 229.3 {+-} 1.9 {+-} 9.0 mb, respectively. Inclusive production cross sections for negatively and positively charged pions are presented as functions of laboratory momentum in ten intervals of the laboratory polar angle covering the range from 0 up to 420 mrad. The spectra are compared with predictions of several hadron production models.
135 citations
University of Tokyo1, Boston University2, Brookhaven National Laboratory3, University of California, Irvine4, California State University, Dominguez Hills5, Chonnam National University6, Duke University7, Fukuoka Institute of Technology8, Gifu University9, Kanagawa University10, Kobe University11, Kyoto University12, Miyagi University of Education13, Nagoya University14, Stony Brook University15, Niigata University16, Okayama University17, Osaka University18, Seoul National University19, Shizuoka University20, Sungkyunkwan University21, Tokai University22, Tsinghua University23, University of Warsaw24, University of Washington25
TL;DR: In this paper, the authors study nonstandard neutrino interactions as an example of physics beyond the standard model using atmospheric neutrinos data collected during the Super-Kamiokande I (1996--2001) and II (2003--2005) periods.
Abstract: In this paper we study nonstandard neutrino interactions as an example of physics beyond the standard model using atmospheric neutrino data collected during the Super-Kamiokande I (1996--2001) and II (2003--2005) periods. We focus on flavor-changing-neutral-currents (FCNC), which allow neutrino flavor transitions via neutral current interactions, and effects which violate lepton nonuniversality and give rise to different neutral-current interaction-amplitudes for different neutrino flavors. We obtain a limit on the FCNC coupling parameter, ${\ensuremath{\epsilon}}_{\ensuremath{\mu}\ensuremath{\tau}}$, $|{\ensuremath{\epsilon}}_{\ensuremath{\mu}\ensuremath{\tau}}|l1.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}$ at 90% C.L. and various constraints on other FCNC parameters as a function of the nonuniversality coupling, ${\ensuremath{\epsilon}}_{ee}$. We find no evidence of nonstandard neutrino interactions in the Super-Kamiokande atmospheric data.
109 citations
University of Tokyo1, Kobe University2, University of California, Irvine3, Autonomous University of Madrid4, Boston University5, Brookhaven National Laboratory6, California State University, Dominguez Hills7, Chonnam National University8, Duke University9, Gifu University10, Kyoto University11, Miyagi University of Education12, Nagoya University13, Stony Brook University14, Okayama University15, Osaka University16, Seoul National University17, Shizuoka University18, Sungkyunkwan University19, Tokai University20, Tsinghua University21, University of Warsaw22, University of Washington23
TL;DR: Best-fit antineutrino mixing is found to be at (Δm2,sin2 2θ)=(2.0×10(-3) eV2, 1.0) and is consistent with the overall Super-K measurement.
Abstract: We present a search for differences in the oscillations of antineutrinos and neutrinos in the Super-Kamiokande-I, -II, and -III atmospheric neutrino sample. Under a two-flavor disappearance model with separate mixing parameters between neutrinos and antineutrinos, we find no evidence for a difference in oscillation parameters. Best-fit antineutrino mixing is found to be at ({Delta}m{sup 2},sin{sup 2}2{theta})= (2.0x10{sup -3} eV{sup 2},1.0) and is consistent with the overall Super-K measurement.
83 citations
Posted Content•
20 Sep 2011
TL;DR: In this article, a search for neutron-antineutron ($n-bar{n}$) oscillation was undertaken in Super-Kamiokande using the 1489 live-day or $2.45 \times 10^{34}$ neutron-year exposure data.
Abstract: A search for neutron-antineutron ($n-\bar{n}$) oscillation was undertaken in Super-Kamiokande using the 1489 live-day or $2.45 \times 10^{34}$ neutron-year exposure data. This process violates both baryon and baryon minus lepton numbers by an absolute value of two units and is predicted by a large class of hypothetical models where the seesaw mechanism is incorporated to explain the observed tiny neutrino masses and the matter-antimatter asymmetry in the Universe. No evidence for $n-\bar{n}$ oscillation was found, the lower limit of the lifetime for neutrons bound in ${}^{16}$O, in an analysis that included all of the significant sources of experimental uncertainties, was determined to be $1.9 \times 10^{32}$~years at the 90\% confidence level. The corresponding lower limit for the oscillation time of free neutrons was calculated to be $2.7 \times 10^8$~s using a theoretical value of the nuclear suppression factor of $0.517 \times 10^{23}$~s$^{-1}$ and its uncertainty.
16 citations
Posted Content•
TL;DR: In this paper, the authors proposed a test experiment to identify and measure charged kaons, including their decays, in liquid argon TPCs, in a momentum range of 540-800 MeV/c, in the K1.1BR beamline of the J-PARC slow extraction facility.
Abstract: At the beginning of 2010, we presented at the J-PARC PAC an R$&$D program towards large (100 kton scale) liquid argon TPCs, suitable to investigate, in conjunction with the J-PARC neutrino beam, the possibility of CP violation in the neutrino sector and to search for nucleon decay. As a first step we proposed a test experiment to identify and measure charged kaons, including their decays, in liquid argon. The detector, a 250L LAr TPC, is exposed to charged kaons, in a momentum range of 540-800 MeV/c, in the K1.1BR beamline of the J-PARC slow extraction facility. This is especially important to estimate efficiency and background for nucleon decay searches in the charged kaon mode ($p \rightarrow \bar{
u} K^+$, etc.), where the kaon momentum is expected to be in the few hundred MeV/c range. A prototype setup has been exposed in the K1.1BR beamline in the fall of 2010. This paper describes the capabilities of the beamline, the construction and setting up of the detector prototype, along with some preliminary results.
10 citations
25 Jul 2011
TL;DR: In this article, the authors investigated the possibility of building a large underground cavern there to install a 100 kton class Giant Liquid Argon Time Projection Chamber (TPC) detector for a neutrino oscillation and proton decay experiment and found that the Okinoshima Island site is a good candidate site for such an observatory.
Abstract: The Okinoshima Islands are located on an off-axis of 0.76 degree (almost on-axis) with the same neutrino beam setting as T2K (2.5 degree off- axis to Kamioka). The distance of Okinoshima from the neutrino source, KEK/J-PARC, is 658 km. This configuration enables to conduct precision measurement of the 1st and 2nd neutrino oscillation maxima of the appearance electron neutrino energy spectrum. We have made studies of the Okinoshima Island site from the geological, geographic and infrastructure points of view to investigate the possibility of building a large underground cavern there to install a 100 kton class Giant Liquid Argon Time Projection Chamber (TPC) detector for a neutrino oscillation and proton decay experiment. We have found that the Okinoshima Island site is a good candidate site for such an observatory.