The Super-Kamiokande detector is a ring imaging Cherenkov detector for neutrino physics and proton-decay search and consists of 50 000 tons of pure water equipped with about 13 000 photo-multipliers. ...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 and a multi-hit Time to Digital converter. TCP/IP based readout channel is implemented to handle large amounts of data. In the new data acquisition 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 470 MB/s, we utilize Gigabit and 10-Gigabit Ethernet technologies 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.
A high performance distillation system to remove krypton from xenon was constructed, and a purity level of Kr/Xe
=
∼3
×
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.
We have searched for proton decay via p→e+π0 and p→μ+π0 using Super-Kamiokande data from April 1996 to March 2015, 0.306 megaton·years exposure in total. The atmospheric neutrino background rate in ...Super-Kamiokande IV is reduced to almost half that of phase I-III by tagging neutrons associated with neutrino interactions. The reach of the proton lifetime is further enhanced by introducing new signal criteria that select the decay of a proton in a hydrogen atom. No candidates were seen in the p→e+π0 search. Two candidates that passed all of the selection criteria for p→μ+π0 have been observed, but these are consistent with the expected number of background events of 0.87. Lower limits on the proton lifetime are set at τ/B(p→e+π0)>1.6×1034 years and τ/B(p→μ+π0)>7.7×1033 years at 90% confidence level.
Super-Kamiokande (SK) can search for weakly interacting massive particles (WIMPs) by detecting neutrinos produced from WIMP annihilations occurring inside the Sun. In this analysis, we include ...neutrino events with interaction vertices in the detector in addition to upward-going muons produced in the surrounding rock. Compared to the previous result, which used the upward-going muons only, the signal acceptances for light (few-GeV/c^{2}-200-GeV/c^{2}) WIMPs are significantly increased. We fit 3903 days of SK data to search for the contribution of neutrinos from WIMP annihilation in the Sun. We found no significant excess over expected atmospheric-neutrino background and the result is interpreted in terms of upper limits on WIMP-nucleon elastic scattering cross sections under different assumptions about the annihilation channel. We set the current best limits on the spin-dependent WIMP-proton cross section for WIMP masses below 200 GeV/c^{2} (at 10 GeV/c^{2}, 1.49×10^{-39} cm^{2} for χχ→bbover ¯ and 1.31×10^{-40} cm^{2} for χχ→τ^{+}τ^{-} annihilation channels), also ruling out some fraction of WIMP candidates with spin-independent coupling in the few-GeV/c^{2} mass range.
A comprehensive study of the atmospheric neutrino flux in the energy region from sub-GeV up to several TeV using the Super-Kamiokande (SK) water Cherenkov detector is presented in this paper. The ...energy and azimuthal spectra, and variation over time, of the atmospheric νe+ν¯e and νμ+ν¯μ fluxes are measured. The energy spectra are obtained using an iterative unfolding method by combining various event topologies with differing energy responses. The azimuthal spectra depending on energy and zenith angle, and their modulation by geomagnetic effects, are also studied. A predicted east-west asymmetry is observed in both the νe and νμ samples at 8.0σ and 6.0σ significance, respectively, and an indication that the asymmetry dipole angle changes depending on the zenith angle was seen at the 2.2σ level. The measured energy and azimuthal spectra are consistent with the current flux models within the estimated systematic uncertainties. A study of the long-term correlation between the atmospheric neutrino flux and the solar magnetic activity cycle is performed, and a weak preference for a correlation was seen at the 1.1σ level, using SK-I–SK-IV data spanning a 20-year period. For several particularly strong solar activity periods, corresponding to Forbush decrease events, no theoretical prediction is available but a deviation below the typical neutrino event rate is seen at the 2.4σ level. The seasonal modulation of the neutrino flux is also examined, but the change in flux at the SK site is predicted to be negligible, and, as expected, no evidence for a seasonal correlation is seen.
A search for Supernova Relic Neutrinos ν¯e’s is first conducted via inverse-beta-decay by tagging neutron capture on hydrogen at Super-Kamiokande-IV. The neutron tagging efficiency is determined to ...be (17.74±0.04stat.±1.05sys.)%, while the corresponding accidental background probability is (1.06±0.01stat.±0.18sys.)%. Using 960days of data, we obtain 13 inverse-beta-decay candidates in the range of Eν¯e between 13.3MeV and 31.3MeV. All of the observed candidates are attributed to background. Upper limits at 90% C.L. are calculated in the absence of a signal.
We present a real-time supernova neutrino burst monitor at Super-Kamiokande (SK). Detecting supernova explosions by neutrinos in real time is crucial for giving a clear picture of the explosion ...mechanism. Since the neutrinos are expected to come earlier than light, a fast broadcasting of the detection may give astronomers a chance to make electromagnetic radiation observations of the explosions right at the onset. The role of the monitor includes a fast announcement of the neutrino burst detection to the world and a determination of the supernova direction. We present the online neutrino burst detection system and studies of the direction determination accuracy based on simulations at SK.
Calibration of the Super-Kamiokande detector Abe, K.; Iyogi, K.; Kameda, J. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
02/2014, Letnik:
737
Journal Article
Recenzirano
Odprti dostop
Procedures and results on hardware-level detector calibration in Super-Kamiokande (SK) are presented in this paper. In particular, we report improvements made in our calibration methods for the ...experimental phase IV in which new readout electronics have been operating since 2008.
The topics are separated into two parts. The first part describes the determination of constants needed to interpret the digitized output of our electronics so that we can obtain physical numbers such as photon counts and their arrival times for each photomultiplier tube (PMT). In this context, we developed an in situ procedure to determine high-voltage settings for PMTs in large detectors like SK, as well as a new method for measuring PMT quantum efficiency and gain in such a detector.
The second part describes modeling of the detector in Monte Carlo simulations, including, in particular, the optical properties of the water target and their variability over time. Detailed studies on water quality are also presented.
As a result of this work, we have achieved a precision sufficient for physics analyses over a wide energy range (from a few MeV to above 1TeV). For example, charge determination was at the level of 1%, and the timing resolution was 2.1ns at the one-photoelectron charge level and 0.5ns at the 100-photoelectron charge level.
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