Disclaimer: machine translated by DeepL which may contain errors.
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Memories of Dr. Masatoshi Koshiba
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Dr. Masatoshi Koshiba, who invented the Kamiokande experiment and founded neutrino astronomy, passed away on November 12, 2020. As one of the students who participated in the Kamiokande experiment under Dr. Koshiba and learned many things from him, I would like to write about my memories of Dr. Koshiba.
Dr. Koshiba at the time of construction of Kamiokande (in the water tank of Kamiokande in 1983)I heard that it was in the late 1970s that Dr. Koshiba came up with the idea of the Kamiokande for the purpose of searching for proton decay. I became a member of his laboratory as a Master's student in the spring of 1981, just as the 50 cm diameter photomultiplier tubes for the Kamiokande were beginning to be manufactured. This 50 cm diameter photomultiplier tube was the key to the success of Kamiokande. At the time, the IMB, an instrument similar in concept to Kamiokande but about three times the size, was being tested in the United States about a year earlier than Kamiokande. In the end, when the experiment was over, I think it can be said that Kamiokande produced far more results thanks to the 50 cm diameter photomultiplier tube.
Dr. Koshiba always said two things to the graduate students in his laboratory. One was, "We are allowed to conduct experiments with the public's blood money. Therefore, do not waste even a single yen of research funds. When you buy something from a vendor, never buy it at the asking price. He also told me to always keep two or three research eggs in my basket so that I would be able to work as an independent researcher in the future, and to be ready to conduct experiments when the time came. I believe that these teachings have been passed on to many people from Koshiba's laboratory.
Kamiokande was started with the aim of observing proton decay, but when the experiment started, no proton decay was observed. On the other hand, after several months of data showed that the spectrum of electrons emitted from cosmic-ray muons that had stopped and decayed in water was clear above about 10 MeV, Dr. Koshiba proposed to modify Kamiokande to observe solar neutrinos whose spectrum extended to 14 MeV. At the time, Dr. Koshiba said, "We can't just end the experiment with the result that no proton decay signal was observed in the Kamiokande, which we spent so much money to build. Dr. Koshiba was putting into practice exactly what he had said to the students in his laboratory. It was surprising to see such a major change of policy just a few months after the start of the experiment, but the timing of the decision eventually led to the supernova neutrino observation in 1987.
Once the Kamiokande experiment began, Dr. Koshiba made it a daily routine to sit in front of the display every morning and scan the Kamiokande data, and he continued to do so. I think he wanted to be the first to confirm with his own eyes the proton decay or any other interesting event. I feel that his attitude taught me something that we, as researchers, must never forget. We pray that Dr. Masatoshi Koshiba may rest in peace.
Faculty of Science News, January 2021