New TDC modules were arranged by the US group. Responding to the proposed detector improvement, a US group (mostly from University of Pennsylvania) joined and the new Collaboration, Kamiokande-II, was formed. It was called Super-Kamiokande (Super-K) soon after their initial naming. In 1984, at ICOBAN84 held in Park City, Utah, the Kamiokande collaboration made two presentations, one was the report on their latest physics results and a possible detector improvement aiming at observing solar neutrinos and another one was a proposal to construct a 22.5 kton water Cherenkov detector called JACK (Japan America Collaboration at Kamioka). Solar neutrinos became an important subject for Kamiokande. ![]() However, Kamiokande was expected to achieve higher energy resolution and lower energy threshold, since 20% of the inner surface was covered by light sensitive photo-cathode, while IMB PMTs covered 2%.Ī few months after the start of Kamiokande, they had realized that they could observe electrons from muon decay down to 15 MeV and recognized that further efforts to lower the detectable energy down to 10 MeV would make it possible to measure solar neutrinos. The target mass of IMB exceeded significantly the one of Kamiokande. In July, 1983, the Kamiokande experiment started to take data while the competitor, the IMB experiment, using \(\sim 8000\) tons of water with \(\sim 5000\) PMTs of 20 cm in diameter had already started 1 year before. Although the primary aim was to conduct an extensive search for proton decay, possibilities to make a study on neutrino oscillations through atmospheric neutrinos and to detect neutrino bursts from supernovae were mentioned in their proposal, however a possible observation of solar neutrinos was not explicitly referred. In 1982, the project called KamiokaNDE (Kamioka Nucleon Decay Experiment) was funded. Koshiba and his colleagues conceived to build a detector of about 2000 tons of water (inner volume) surrounded by \(\sim 1000\) PMTs (photo-multiplier tubes) of 50 cm in diameter to look for proton decay to test grand unified theories. ![]() Nevertheless, we now know that the estimated lifetime was considerably underestimated. They said in the paper that “It makes just one easily testable prediction, \(\hbox \) nucleons and a race with underground experiments started. In 1974, Georgi and Glashow presented a first realistic model of the grand unification based upon SU(5). The beginning of the story goes back to the middle of 70’s when particle physicists had started to discuss their dream to unify the weak, electromagnetic and strong interactions, the gauge group of SU(2) \(\times \) U(1) \(\times \) SU(3), by a single larger gauge group. Much of the historical information written here about Kamiokande comes from the recollections of the Kamiokande collaborators and references. We first refer to “Kamiokande” briefly, the predecessor of Super-K, as a prehistory. This report describes the history and the physics results of the Super-K experiment. Super-Kamiokande (Super-K, hereafter), the world largest imaging water Cherenkov detector, has been operated for more than 20 years since 1996, performed detailed studies on neutrino properties, and eventually led to the discovery of neutrino oscillations opening up a new field of research. The prospects for the future of Super-K are also described. In this article, we report mostly on the studies of the neutrino oscillations by Super-K in a historical context. ![]() The Super-K detector has also been used as a far detector of the long baseline neutrino oscillation experiments, K2K and T2K. Following those historical discoveries, numerous intriguing results have been obtained by Super-K, like the discovery of oscillatory behavior, tau appearance in the atmospheric neutrinos, the matter effect of the solar neutrinos through the earth. In 2001 SNO in Canada together with the Super-K data established that solar neutrinos are also oscillating. Super-K started data taking on 1st of April in 1996 after 5 years construction period and obtained compelling evidence of atmospheric neutrino oscillations in 1998, shortly after the beginning of the experiment. Super-Kamiokande is a gigantic and versatile detector able to detect neutrinos with energies between a few MeV and a few hundred GeV.
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