A Direct Search For Weakly Interacting Massive Particles In The Super-kamiokande Experiment

Weakly Interacting Massive Particle (WIMP) is believed to be a major constituentof cold dark matter―the main component of the matter composition in the universe.This study is an attempt to search for decay of charged excited WIMPs in the world'slargest water Cherenkov detector―the Super-Kamiokande Detector in Japan. The dataacquisition system in the Super-Kamiokande Experiment was upgraded in September,2008 and since then the Super-Kamiokande Experiment has been in Phase IV. Thiswork consists of three parts, which are the time calibration study, the particle identifi-cation study and a direct search for decay of charged excited WIMPs.To begin with, this work studies the time calibration of the photo-multiplier tubes(PMTs) in Super-Kamiokande IV within the dynamic range of 0?1000 p.e.. On the onehand, the study provides precise time calibration constants for relative time responses,which are utilized to reduce relative time responses from a maximum of about 25 ns towithin 0.52 ns. On the other hand, the relation between the time resolution and thecharge is also studied. The result is used by Monte Carlo simulation as input. A checkof the time resolution shows that Monte Carlo simulation is in good agreement withreal data.Moreover, this work studies the particle identification in Super-Kamiokande IV.Mis-identification probabilities of particle types are estimated using the cosmic stopmuon sample. For real data, the probability for showering particles (e.g. electrons,gamma) to be mis-identified as non-showering particles (e.g. muons, charged pi-ons) is 1.25±0.04%, and the probability for non-showering particles to be mis-identified as showering particles is 0.032±0.006%. Within statistical uncertainties,mis-identification probabilities almost remain stable over the running period.Finally, utilizing the events that only cause hits in the inner detector with alltheir final state charged particles contained in the inner detector (FC events) takenin 289.092 live-days from October, 2008 to October, 2009 in Super-Kamiokande IV, a direct search for decay of charged excited WIMPs into three charged leptons or threecharged leptons plus light neutral particles is performed. Within the above FC sample,no signal event is found. An estimation shows that the -ux of the particles with theabove signature is below 3×10^-15 cm^-2s^-1 (90% CL).