T. Iida

Bio: T. Iida is an academic researcher from University of Tokyo. The author has contributed to research in topics: Super-Kamiokande & Neutrino. The author has an hindex of 5, co-authored 5 publications receiving 710 citations.

Solar neutrino measurements in Super-Kamiokande-II

Abstract: The results of the second phase of the Super-Kamiokande solar neutrino measurement are presented and compared to the first phase. The solar neutrino flux spectrum and time variation as well as oscillation results are statistically consistent with the first phase and do not show spectral distortion. The time-dependent flux measurement of the combined first and second phases coincides with the full period of solar cycle 23 and shows no correlation with solar activity. The measured {sup 8}B total flux is (2.38{+-}0.05(stat.){sub -0.15}{sup +0.16}(sys.))x10{sup 6} cm{sup -2} s{sup -1} and the day-night difference is found to be (-6.3{+-}4.2(stat.){+-}3.7(sys.))%. There is no evidence of systematic tendencies between the first and second phases.

Search for Supernova Neutrino Bursts at Super-Kamiokande

Abstract: We report the results of a search for neutrino bursts from supernova explosions using the Super-Kamiokande detector. Super-Kamiokande is sensitive to core-collapse supernova explosions via observation of their neutrino emissions. The expected number of events comprising such a burst is ~104, and the average energy of the neutrinos is in the range of a few tens of MeV for a core-collapse supernova explosion at a typical distance in our galaxy (10 kpc); this strong signal means that the detection efficiency anywhere within our galaxy and well past the Magellanic Clouds should be 100%. We examined a data set taken from 1996 May to 2001 July, and from 2002 December to 2005 October, corresponding to 2589.2 live days. However, there is no evidence of such a supernova explosion during the data-taking period. The 90% C.L. upper limit on the rate of core-collapse supernova explosions out to distances of 100 kpc is found to be 0.32 SN yr-1.

Measurement of Atmospheric Neutrino Flux Consistent with Tau Neutrino Appearance

Abstract: A search for the appearance of tau neutrinos from ${\ensuremath{ u}}_{\ensuremath{\mu}}\ensuremath{\leftrightarrow}{\ensuremath{ u}}_{\ensuremath{\tau}}$ oscillations in the atmospheric neutrinos has been performed using 1489.2 days of atmospheric neutrino data from the Super-Kamiokande-I experiment. A best fit tau neutrino appearance signal of $138\ifmmode\pm\else\textpm\fi{}48(\mathrm{stat}{)}_{\ensuremath{-}32}^{+15}(\mathrm{syst})$ events is obtained with an expectation of $78\ifmmode\pm\else\textpm\fi{}26(\mathrm{syst})$. The hypothesis of no tau neutrino appearance is disfavored by 2.4 sigma.

High-energy neutrino astronomy using upward-going muons in super-kamiokande I

Abstract: We present the results from several studies used to search for astrophysical sources of high-energy neutrinos using the Super-Kamiokande I (1996 April-2001 July) neutrino-induced upward-going muon data. The data set consists of 2359 events with minimum energy 1.6 GeV, of which 1892 are through-going and 467 stop within the detector. The results of several independent analyses are presented, including searches for point sources using directional and temporal information and a search for signatures of cosmic-ray interactions with the interstellar medium in the upward-going muons. No statistically significant evidence for point sources or any diffuse flux from the plane of the Galaxy was found, so specific limits on fluxes from likely point sources are calculated. The 90% confidence level (CL) upper limits on upward-going muon flux from astronomical sources that are located in the southern hemisphere and always under the horizon for Super-Kamiokande are ~ × 10-15 cm-2 s-1.

Search for Diffuse Astrophysical Neutrino Flux Using Ultra-High-Energy Upward-going Muons in Super-Kamiokande I

Abstract: Many astrophysical models predict a diffuse flux of high-energy neutrinos from active galactic nuclei and other extragalactic sources. At muon energies above 1 TeV, the upward-going muon flux induced by neutrinos from active galactic nuclei is expected to exceed the flux due to atmospheric neutrinos. We have performed a search for this astrophysical neutrino flux by looking for upward-going muons in the highest energy data sample from the Super-Kamiokande detector using 1679.6 live days of data. We found one extremely high energy upward-going muon event, compared with an expected atmospheric neutrino background of 0.46 ± 0.23 events. Using this result, we set an upper limit on the diffuse flux of upward-going muons due to neutrinos from astrophysical sources in the muon energy range 3.16-100 TeV.

Updated fit to three neutrino mixing: exploring the accelerator-reactor complementarity

Abstract: We perform a combined fit to global neutrino oscillation data available as of fall 2016 in the scenario of three-neutrino oscillations and present updated allowed ranges of the six oscillation parameters. We discuss the differences arising between the consistent combination of the data samples from accelerator and reactor experiments compared to partial combinations. We quantify the confidence in the determination of the less precisely known parameters θ 23, δ CP, and the neutrino mass ordering by performing a Monte Carlo study of the long baseline accelerator and reactor data. We find that the sensitivity to the mass ordering and the θ 23 octant is below 1σ. Maximal θ 23 mixing is allowed at slightly more than 90% CL. The best fit for the CP violating phase is around 270°, CP conservation is allowed at slightly above 1σ, and values of δ CP ≃ 90° are disfavored at around 99% CL for normal ordering and higher CL for inverted ordering.

The fate of hints: updated global analysis of three-flavor neutrino oscillations

Abstract: Our herein described combined analysis of the latest neutrino oscillation data presented at the Neutrino2020 conference shows that previous hints for the neutrino mass ordering have significantly decreased, and normal ordering (NO) is favored only at the 1.6σ level. Combined with the χ2 map provided by Super-Kamiokande for their atmospheric neutrino data analysis the hint for NO is at 2.7σ. The CP conserving value δCP = 180° is within 0.6σ of the global best fit point. Only if we restrict to inverted mass ordering, CP violation is favored at the ∼ 3σ level. We discuss the origin of these results — which are driven by the new data from the T2K and NOvA long-baseline experiments —, and the relevance of the LBL-reactor oscillation frequency complementarity. The previous 2.2σ tension in ∆m221 preferred by KamLAND and solar experiments is also reduced to the 1.1σ level after the inclusion of the latest Super-Kamiokande solar neutrino results. Finally we present updated allowed ranges for the oscillation parameters and for the leptonic Jarlskog determinant from the global analysis.

Updated fit to three neutrino mixing: status of leptonic CP violation

Abstract: We present a global analysis of solar, atmospheric, reactor and accelerator neutrino data in the framework of three-neutrino oscillations based on data available in summer 2014. We provide the allowed ranges of the six oscillation parameters and show that their determination is stable with respect to uncertainties related to reactor neutrino and solar neutrino flux predictions. We find that the maximal possible value of the Jarlskog invariant in the lepton sector is 0.033 ±0.010 (±0.027) at the 1σ (3σ) level and we use leptonic unitarity triangles to illustrate the ability of global oscillation data to obtain information on CP violation. We discuss “tendencies and tensions” of the global fit related to the octant of θ 23 as well as the CP violating phase δ CP. The favored values of δ CP are around 3π/2 while values around π/2 are disfavored at about Δχ2 ≃6. We comment on the non-trivial task to assign a confidence level to this Δχ 2 value by performing a Monte Carlo study of T2K data.

Global fit to three neutrino mixing: critical look at present precision

Abstract: We present an up-to-date global analysis of solar, atmospheric, reactor, and accelerator neutrino data in the framework of three-neutrino oscillations. We provide results on the determination of θ 13 from global data and discuss the dependence on the choice of reactor fluxes. We study in detail the statistical significance of a possible deviation of θ 23 from maximal mixing, the determination of its octant, the ordering of the mass states, and the sensitivity to the CP violating phase, and discuss the role of various complementary data sets in those respects.