"Some as-yet-unaccounted-for physics might be necessary to explain the result."
This was written by Professor Takaaki Kajita and his colleagues in 1988 after they had seen puzzling results from the Kamiokande neutrino detector in Japan. There was a discrepancy in how many neutrinos of a certain type they observed, and it seemed to depend on how far away the subatomic particle was from the detector when it was created.
The Kamiokande experiment at the time was an ambitious attempt to detect elusive neutrinos. It comprised a tank containing 3,000 tons of pure water buried a kilometre underground in the Kamioka mine. It needed to be isolated enough to be shielded from cosmic rays, and large enough to detect the very rare occasions when a passing neutrino interacts with a water molecule.
The initial results did not agree with the theoretical predictions. "I thought it was a mistake in the data analysis”, remembers Prof Kajita, “Or could it be a hint at an unexpected phenomenon?". He would later declare this period as the most exciting time in his life as a physicist.
It would take another ten years before he had the answer. Prof Kajita presented his findings at the 1998 International Conference on Neutrino Physics and Astrophysics, saying he had found enough compelling evidence to show that neutrinos could transform themselves over time. Neutrinos that travel further have more time to turn into different types, lowering the apparent count.
His announcement was lauded by a standing ovation, and seventeen years later, in 2015, he received an even greater accolade, winning the Nobel Prize in Physics.
Today, Proj Kajita has changed his research focus from studying neutrinos to gravity waves, saying “I wanted to do something new and exciting.” He is currently developing the Hyper-Kamiokande, which will be nearly 90 times bigger than the original Kamioka mine. Experiments are expected to start at the new facility in 2027, which has been built at a cost of US$600 million. More than 400 scientists from 19 countries have shown interest in research collaborations at the new facility.
Prof Kajita is currently a Distinguished Professor at the University of Tokyo, a Member of the prestigious Japan Academy and also the Director of the Next-generation Neutrino Science Organisation.
Nobel Prize in Physics