M. Shiozawa

Indications of neutrino oscillation in a 250 km long-baseline experiment.

The K2K experiment observes indications of neutrino oscillation: a reduction of nu(mu) flux together with a distortion of the energy spectrum. Fifty-six beam neutrino events are observed in Super-Kamiokande (SK), 250 km from the neutrino production point, with an expectation of 80.1(+6.2)(-5.4). Twenty-nine one ring mu-like events are used to reconstruct the neutrino energy spectrum, which is better matched to the expected spectrum with neutrino oscillation than without. The probability that the observed flux at SK is explained by statistical fluctuation without neutrino oscillation is less than 1%.

Atmospheric muon-neutrino / electron-neutrino ratio in the multiGeV energy range

Abstract Data from the Kamiokande detector were used to study the atmospheric (v μ + v μ ) (v e + v e ) ratio in the multi-GeV energy range. The observed ratio of μ-like to e-like events relative to the calculated ratio, ( μ /e) data /( μ /e) MC = 0.57 -0.07 +0.08 ± 0.07, suggests that the atmospheric (v μ + v μ ) (v e + v e ) ratio is smaller than expected for these neutrino energies. Also studied was the zenith-angle dependence of the above ratio. Results of an analysis of neutrino oscillations are presented.

Measurement of the flux and zenith angle distribution of upward through going muons in Kamiokande II + III

The flux of upward through-going muons of minimum (mean) threshold energy > 1.6 (3.0) GeV is measured, based on a total of 372 events observed by the Kamiokande II+III detector during 2456 detector live days. The observed muon flux was (1.94+-0.10(stat.)+0.07-0.06(sys.))*10^-13 /cm^2/s/sr, which is compared to an expected value of (2.46+-0.54(theo.))*10^-13/cm^2/s/sr. The observation is in agreement with the prediction within the errors. The zenith angle dependence of the observed upward through-going muons supports the previous indication of neutrino oscillations made by Kamiokande using sub- and multi-GeV atmospheric neutrino events.

Distillation of Liquid Xenon to Remove Krypton

A high performance distillation system to remove krypton from xenon was constructed, and a purity level

A study on the eμ identification capability of a water Čerenkov detector and the atmospheric neutrino problem

Abstract We carried out an experimental test of various characteristics of a water Cerenkov detector, especially the particle identification capability, using the 12-GeV proton synchrotron at KEK, Japan. The detector characteristics so far studied are well reproduced by the Monte Carlo simulation. Especially it is able to identify electrons and muons with mis-identification probabilities less than a few percent in the momentum range of 250–1000 MeV/c except the particle positions in the extreme edge of the detector volume. Based on the present results, the deficiency of μ-neutrinos in the atmospheric neutrinos is not an artifact caused by some peculiar detector characteristics.

Search for Proton Decay via

We have searched for proton decay via p→νK+ using Super-Kamiokande data from April 1996 to February 2013, 260 kiloton•year exposure in total. No evidence for this proton decay mode is found. A lower limit of the proton lifetime is set to τ/B(p→νK+)>5.9×1033 years at 90% confidence level.

p \rightarrow \nu K^{+}

Abstract The Super-Kamiokande experiment, using a large underground water Cherenkov detector, has started its operation since first April, 1996. One of the main physics goals of this experiment is to measure the atmospheric neutrinos. Proton decay search is also an important topic. For these analyses, all measurement of physical quantities of an event such as vertex position, the number of Cherenkov rings, momentum, particle type and the number of decay electrons, is automatically performed by reconstruction algorithms. We attain enough quality of the analyses using these algorithms and several impressive results have been addressed.

using 260 kiloton

The Super-Kamiokande (SK) detector is a ring imaging Cherenkov detector for neutrino physics and proton-decay search and consists of 50000 tons of pure water equipped with about 13000 photo-multipliers (PMTs). The old front-end electronics and online system running for more than one decade were all upgraded in September, 2008 and the data acquisition was started successfully. The new front-end electronics is based on a charge to time converter (QTC) and a multi-hit TDC. TCP/IP based readout channel is implemented to handle large amounts of data. In the new data acquisition (DAQ) scheme, the hardware event-trigger for the data reduction is replaced by processing all the hits in the online farm, so that we are able to lower the threshold of the detection energy for solar neutrino and analyze consecutive events whose time interval is too long to detect in the previous system. To make the new online system to be capable of processing larger dataflow of up to 470MB/s, we utilize Gigabit and 10Gigabit Ethernet techniques and distribute the load over Linux PCs to handle a large amount of data. In this paper, we will describe the design and performance of the new system in the commissioning.

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Abstract Neutron background in the atmospheric neutrino sample was studied based on the vertex position distribution of the fully contained π 0 events. No evidence for the background contamination was observed. The neutron contamination in the sub-GeV e-like sample was less than 1.2% at 90% C.L.

year data of Super-Kamiokande

Super-Kamiokande is a ring imaging water Cherenkov detector for astro-particle physics that consists of 50 kton pure water and about 13000 photomultiplier tubes (PMTs). We are planning to upgrade all the front-end electronics in next year. By high speed signal processing electronics, we will record all the hits of all the PMTs without any hardware filtering, aiming observations of much fainter signals of the supernova relic neutrinos, lower energy (~3 MeV) solar neutrinos, neutrino burst from nearby galactic supernova, and so on. The energy resolutions of multi-GeV atmospheric neutrino events will also be improved by the electronics. The new front-end electronics is based on a charge to time converter (QTC) and a multi-hit TDC. TCP/IP based readout channel is implemented to handle large amounts of data. We have developed a custom ASIC QTC and evaluated the characteristics of the chip and the prototypical board; high-speed (1 MHz cycle), high sensitivity for single photo-electron signal, good charge (0.1 pC RMS) and timing (0.3 ns RMS) responses, and wide charge dynamic range (2500 pC). In this paper, the design and the performance of the front-end board are discribed.