arXiv subjects

Y. Fukuda

Publications and source records attributed to Y. Fukuda.

At least 181 records · Page 10Linked to original sources

arXiv2012

Search for GUT Monopoles at Super-Kamiokande

GUT monopoles captured by the Sun's gravitation are expected to catalyze proton decays via the Callan-Rubakov process. In this scenario, protons, which initially decay into pions, will ultimately produce ν_{e}, ν_μ and \barν_μ. After undergoing neutrino oscillation, all neutrino species appear when they arrive at the Earth, and can be detected by a 50,000 metric ton water Cherenkov detector, Super-Kamiokande (SK). A search for low energy neutrinos in the electron total energy range from 19 to 55 MeV was carried out with SK and gives a monopole flux limit of F_M(σ_0/1 mb) < 6.3 \times 10^{-24} (β_M/10^{-3})^2 cm^{-2} s^{-1} sr^{-1} at 90% C.L., where β_M is the monopole velocity in units of the speed of light and σ_0 is the catalysis cross section at β_M=1. The obtained limit is more than eight orders of magnitude more stringent than the current best cosmic-ray supermassive monopole flux limit, F_M < 1 \times 10^{-15} cm^{-2} s^{-1} sr^{-1} for β_M < 10^{-3} and also two orders of magnitude lower than the result of the Kamiokande experiment, which used a similar detection method.

hep-ex↗

arXiv2012

First Muon-Neutrino Disappearance Study with an Off-Axis Beam

We report a measurement of muon-neutrino disappearance in the T2K experiment. The 295-km muon-neutrino beam from Tokai to Kamioka is the first implementation of the off-axis technique in a long-baseline neutrino oscillation experiment. With data corresponding to 1.43 10**20 protons on target, we observe 31 fully-contained single muon-like ring events in Super-Kamiokande, compared with an expectation of 104 +- 14 (syst) events without neutrino oscillations. The best-fit point for two-flavor nu_mu -> nu_tau oscillations is sin**2(2 theta_23) = 0.98 and |Δm**2_32| = 2.65 10**-3 eV**2. The boundary of the 90 % confidence region includes the points (sin**2(2 theta_23),|Δm**2_32|) = (1.0, 3.1 10**-3 eV**2), (0.84, 2.65 10**-3 eV**2) and (1.0, 2.2 10**-3 eV**2).

hep-ex↗

arXiv2012

Soft X-ray harmonic comb from relativistic electron spikes

We demonstrate a new high-order harmonic generation mechanism reaching the `water window' spectral region in experiments with multi-terawatt femtosecond lasers irradiating gas jets. A few hundred harmonic orders are resolved, giving uJ/sr pulses. Harmonics are collectively emitted by an oscillating electron spike formed at the joint of the boundaries of a cavity and bow wave created by a relativistically self-focusing laser in underdense plasma. The spike sharpness and stability are explained by catastrophe theory. The mechanism is corroborated by particle-in-cell simulations.

physics.plasm-ph↗

arXiv2011

Identification of high energy ions using backscattered particles in laser-driven ion acceleration with cluster-gas targets

A new diagnosis method for high energy ions utilizing a single CR-39 detector mounted on plastic plates is demonstrated to identify the presence of the high energy component beyond the CR-39's detection threshold limit. On irradiation of the CR-39 detector unit with a 25 MeV per nucleon He ion beam from conventional rf-accelerators, a large number of etch pits having elliptical opening shapes are observed on the rear surface of the CR-39. Detailed investigations reveal that these etch pits are created by heavy ions inelastically backscattered from the plastic plates. This ion detection method is applied to laser-driven ion acceleration experiments using cluster-gas targets, and ion signals with energies up to 50 MeV per nucleon are identified.

physics.plasm-ph↗

arXiv2011

Supernova Relic Neutrino Search at Super-Kamiokande

A new Super-Kamiokande (SK) search for Supernova Relic Neutrinos (SRNs) was conducted using 2853 live days of data. Sensitivity is now greatly improved compared to the 2003 SK result, which placed a flux limit near many theoretical predictions. This more detailed analysis includes a variety of improvements such as increased efficiency, a lower energy threshold, and an expanded data set. New combined upper limits on SRN flux are between 2.8 and 3.0 nu_e cm^-2 s^-1 > 16 MeV total positron energy (17.3 MeV E_nu).

hep-ex↗

arXiv2011

Measurements of the T2K neutrino beam properties using the INGRID on-axis near detector

Precise measurement of neutrino beam direction and intensity was achieved based on a new concept with modularized neutrino detectors. INGRID (Interactive Neutrino GRID) is an on-axis near detector for the T2K long baseline neutrino oscillation experiment. INGRID consists of 16 identical modules arranged in horizontal and vertical arrays around the beam center. The module has a sandwich structure of iron target plates and scintillator trackers. INGRID directly monitors the muon neutrino beam profile center and intensity using the number of observed neutrino events in each module. The neutrino beam direction is measured with accuracy better than 0.4 mrad from the measured profile center. The normalized event rate is measured with 4% precision.

physics.ins-det↗

arXiv2011

Search for Differences in Oscillation Parameters for Atmospheric Neutrinos and Antineutrinos at Super-Kamiokande

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 (dm2bar, sin2 2 thetabar) = (2.0x10^-3 eV^2, 1.0) and is consistent with the overall Super-K measurement.

hep-ex↗

arXiv2011

Letter of Intent: The Hyper-Kamiokande Experiment --- Detector Design and Physics Potential ---

We propose the Hyper-Kamiokande (Hyper-K) detector as a next generation underground water Cherenkov detector. It will serve as a far detector of a long baseline neutrino oscillation experiment envisioned for the upgraded J-PARC, and as a detector capable of observing -- far beyond the sensitivity of the Super-Kamiokande (Super-K) detector -- proton decays, atmospheric neutrinos, and neutrinos from astronomical origins. The baseline design of Hyper-K is based on the highly successful Super-K, taking full advantage of a well-proven technology. (to be continued)

hep-ex↗

arXiv2011

Study of Non-Standard Neutrino Interactions with Atmospheric Neutrino Data in Super-Kamiokande I and II

In this paper we study non-standard 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 non-universality (NU) and give rise to different neutral-current interaction-amplitudes for different neutrino flavors. We obtain a limit on the FCNC coupling parameter, varepsilon_{mu tau}, |varepsilon_{mu tau}|<1.1 x 10^{-2} at 90%C.L. and various constraints on other FCNC parameters as a function of the NU coupling, varepsilon_{e e}. We find no evidence of non-standard neutrino interactions in the Super-Kamiokande atmospheric data.

hep-ex↗

arXiv2011

A Study of Reactor Neutrino Monitoring at Experimental Fast Reactor JOYO

We carried out a study of neutrino detection at the experimental fast reactor JOYO using a 0.76 tons gadolinium loaded liquid scintillator detector. The detector was set up on the ground level at 24.3m from the JOYO reactor core of 140MW thermal power. The measured neutrino event rate from reactor on-off comparison was 1.11\pm1.24(stat.)\pm0.46(syst.)events/day. Although the statistical significance of the measurement was not enough, the background in such a compact detector at the ground level was studied in detail and MC simulation was found to describe the data well. A study for improvement of the detector for future such experiments is also shown.

hep-ex↗

arXiv2011

Indication of Electron Neutrino Appearance from an Accelerator-produced Off-axis Muon Neutrino Beam

The T2K experiment observes indications of $ν_μ\rightarrow ν_e$ appearance in data accumulated with $1.43\times10^{20}$ protons on target. Six events pass all selection criteria at the far detector. In a three-flavor neutrino oscillation scenario with $|Δm_{23}^2|=2.4\times10^{-3}$ eV$^2$, $\sin^2 2θ_{23}=1$ and $\sin^2 2θ_{13}=0$, the expected number of such events is 1.5$\pm$0.3(syst.). Under this hypothesis, the probability to observe six or more candidate events is 7$\times10^{-3}$, equivalent to 2.5$σ$ significance. At 90% C.L., the data are consistent with 0.03(0.04)$<\sin^2 2θ_{13}<$ 0.28(0.34) for $δ_{\rm CP}=0$ and a normal (inverted) hierarchy.

hep-ex↗

arXiv2011

Scintillation-only Based Pulse Shape Discrimination for Nuclear and Electron Recoils in Liquid Xenon

In a dedicated test setup at the Kamioka Observatory we studied pulse shape discrimination (PSD) in liquid xenon (LXe) for dark matter searches. PSD in LXe was based on the observation that scintillation light from electron events was emitted over a longer period of time than that of nuclear recoil events, and our method used a simple ratio of early to total scintillation light emission in a single scintillation event. Requiring an efficiency of 50% for nuclear recoil retention we reduced the electron background to 7.7\pm1.1(stat)\pm1.2 0.6(sys)\times10-2 at energies between 4.8 and 7.2 keVee and to 7.7\pm2.8(stat)\pm2.5 2.8(sys)\times10-3 at energies between 9.6 and 12 keVee for a scintillation light yield of 20.9 p.e./keV. Further study was done by masking some of that light to reduce this yield to 4.6 p.e./keV, the same method results in an electron event reduction of 2.4\pm0.2(stat)\pm0.3 0.2(sys)\times10-1 for the lower of the energy regions above. We also observe that in contrast to nuclear recoils the fluctuations in our early to total ratio for electron events are larger than expected from statistical fluctuations.

physics.ins-det↗

arXiv2010

Three- and four-nucleon absorption processes observed in the $K^-$-$^4$He reaction at rest

Correlations of back-to-back coincident $Λd$ and $Λt$ pairs from the stopped $K^-$ reaction on $^4$He had been investigated, thereby $Λd$ and $Λt$ branches of non-mesonic three- and four-nucleon absorption processes of antikaon at rest were identified as well-separable processes, respectively. The branching ratio of the three-nucleon process, ($^4$He-$K^-$)$_{atomic} \rightarrow Λd "n"$, is estimated to be $(0.9 \pm 0.1 (stat) \pm 0.2 (syst)) \times 10^{-3}$ from the normalized $Λd$ spectrum in a $Λd n$ final state, while the fraction of the four-nucleon process, ($^4$He-$K^-$)$_{atomic} \rightarrow Λt$, is obtained to be $(3.1 \pm 0.4 (stat) \pm 0.5 (syst)) \times 10^{-4}$ per stopped $K^-$.

nucl-ex↗

arXiv2010

Atmospheric neutrino oscillation analysis with sub-leading effects in Super-Kamiokande I, II, and III

We present a search for non-zero theta_{13} and deviations of sin^2 theta_{23} from 0.5 in the oscillations of atmospheric neutrino data from Super-Kamiokande -I, -II, and -III. No distortions of the neutrino flux consistent with non-zero theta_{13} are found and both neutrino mass hierarchy hypotheses are in agreement with the data. The data are best fit at Delta m^2 = 2.1 x 10^-3 eV^2, sin^2 theta_{13} = 0.0, and sin^2 theta_{23} =0.5. In the normal (inverted) hierarchy theta_{13} and Delta m^2 are constrained at the one-dimensional 90% C.L. to sin^2 theta_{13} < 0.04 (0.09) and 1.9 (1.7) x 10^-3 < Delta m^2 < 2.6 (2.7) x 10^-3 eV^2. The atmospheric mixing angle is within 0.407 <= sin^2 theta_{23} <= 0.583 at 90% C.L.

hep-ex↗

arXiv2009

Spallative ablation of dielectrics by X-ray laser

Short laser pulse in wide range of wavelengths, from infrared to X-ray, disturbs electron-ion equilibrium and rises pressure in a heated layer. The case where pulse duration $τ_L$ is shorter than acoustic relaxation time $t_s$ is considered in the paper. It is shown that this short pulse may cause thermomechanical phenomena such as spallative ablation regardless to wavelength. While the physics of electron-ion relaxation on wavelength and various electron spectra of substances: there are spectra with an energy gap in semiconductors and dielectrics opposed to gapless continuous spectra in metals. The paper describes entire sequence of thermomechanical processes from expansion, nucleation, foaming, and nanostructuring to spallation with particular attention to spallation by X-ray pulse.

physics.optics↗

arXiv2009

Self-shielding effect of a single phase liquid xenon detector for direct dark matter search

Liquid xenon is a suitable material for a dark matter search. For future large scale experiments, single phase detectors are attractive due to their simple configuration and scalability. However, in order to reduce backgrounds, they need to fully rely on liquid xenon's self-shielding property. A prototype detector was developed at Kamioka Observatory to establish vertex and energy reconstruction methods and to demonstrate the self-shielding power against gamma rays from outside of the detector. Sufficient self-shielding power for future experiments was obtained.

astro-ph.CO↗

arXiv2009

Novel path towards compact laser ion accelerators for hadron therapy: Tenfold energy increase in laser-driven multi-MeV ion generation using a gas target mixed with submicron clusters

We demonstrate generation of 10-20 MeV/u ions with a compact 4 TW laser using a gas target mixed with submicron clusters, corresponding to tenfold increase in the ion energies compared to previous experiments with solid targets. It is inferred that the high energy ions are generated due to formation of a strong dipole vortex structure. The demonstrated method has a potential to construct compact and high repetition rate ion sources for hadron therapy and other applications.

physics.plasm-ph↗

arXiv2009

Distillation of Liquid Xenon to Remove Krypton

A high performance distillation system to remove krypton from xenon was constructed, and a purity level of Kr/Xe = $\sim 3 \times 10^{-12}$ was achieved. This development is crucial in facilitating high sensitivity low background experiments such as the search for dark matter in the universe.

physics.ins-det↗