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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).
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We calculate the Supernova Relic Neutrino (SRN) background flux for the KamLAND and Super-Kamiokande (SK) detectors, motivated by the reduction in background at SK and new results for the star formation history (e.g., from the Sloan Digital Sky Survey (SDSS)). Our best estimate for the flux at SK is slightly below, but very close to the current SK upper limit. The SK upper limit is already inconsistent with a range of star formation histories allowed by the SDSS data. We estimate that the SRN background should be detected (at 1-sigma) at SK with a total of about 9 years (including the existing 4 years) of data. While KamLAND is a much smaller detector compared to SK, it profits from being practically background-free and from its sensitivity to the lower energy supernova neutrinos. KamLAND could make a 1-sigma detection of the SRN with a total of about 5 years of data. Given the small expected SRN event rate, we also consider the detection of the SRN in a modified SK detector with a lower threshold and reduced background where the time to detection can be reduced by a factor of 10 relative to the existing SK estimate.
The result of a search for neutrino bursts from supernova explosions using the Super-Kamiokande detector is reported. 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 ~10^4 and the average energy of the neutrinos is in few tens of MeV range in the case of a core-collapse supernova explosion at the typical distance in our galaxy (10 kiloparsecs); this large signal means that the detection efficiency anywhere within our galaxy and well past the Magellanic Clouds is 100%. We examined a data set which was taken from May, 1996 to July, 2001 and from December, 2002 to October, 2005 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 kiloparsecs is found to be 0.32 SN/year.
GUT monopoles captured by the Suns gravitation are expected to catalyze proton decays via the Callan-Rubakov process. In this scenario, protons, which initially decay into pions, will ultimately produce u_{e}, u_{mu} and bar{ u}_{mu}. 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(sigma_0/1 mb) < 6.3 times 10^{-24} (beta_M/10^{-3})^2 cm^{-2} s^{-1} sr^{-1} at 90% C.L., where beta_M is the monopole velocity in units of the speed of light and sigma_0 is the catalysis cross section at beta_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 beta_M < 10^{-3} and also two orders of magnitude lower than the result of the Kamiokande experiment, which used a similar detection method.
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.
A search for dinucleon decay into pions with the Super-Kamiokande detector has been performed with an exposure of 282.1 kiloton-years. Dinucleon decay is a process that violates baryon number by two units. We present the first search for dinucleon decay to pions in a large water Cherenkov detector. The modes $^{16}$O$(pp) rightarrow$ $^{14}$C$pi^{+}pi^{+}$, $^{16}$O$(pn) rightarrow$ $^{14}$N$pi^{+}pi^{0}$, and $^{16}$O$(nn) rightarrow$ $^{14}$O$pi^{0}pi^{0}$ are investigated. No significant excess in the Super-Kamiokande data has been found, so a lower limit on the lifetime of the process per oxygen nucleus is determined. These limits are: $tau_{pprightarrowpi^{+}pi^{+}} > 7.22 times 10^{31}$ years, $tau_{pnrightarrowpi^{+}pi^{0}} > 1.70 times 10^{32}$ years, and $tau_{nnrightarrowpi^{0}pi^{0}} > 4.04 times 10^{32}$ years. The lower limits on each mode are about two orders of magnitude better than previous limits from searches for dinucleon decay in iron.
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