For the second time in a little over a decade, the Nobel prize in physics has been awarded to scientists working on neutrinos. Calling these elusive particles “the most abundant inhabitants of the world,” the committee announced that the >physics prize this year would go to Takaaki Kajita of the Super Kamiokande detector, Tokyo, and Arthur Mc Donald of the Sudbury Neutrino Observatory, Canada, for their work in detecting neutrino oscillations – a process by which neutrinos transform from one type to another.
Earlier, in 2002, Raymond Davis and Masatoshi Koshiba were awarded the Nobel prize for detection of cosmic neutrinos.
Asked how he felt on receiving the prize, “It is a very daunting experience” said Prof. Mc Donald whom the Nobel committee connected to the assembled members of the press by telephone after the announcement of the prize. He also recalled the efforts of his numerous colleagues and the friendly collaboration with other experimental groups. About other important questions in neutrino physics, Prof. Mc Donald said, “We know the differences in mass but not the absolute mass of the neutrinos. We do not know what the mass of the lightest among the three of them is.” He referred to the neutrinoless double beta decay experiment as an important means of understanding this.
Neutrinos are chargeless and nearly massless particles that come in three types, or flavours — electron neutrinos, muon neutrinos and tau neutrinos. These are incident on the earth in millions and come from all directions. They originate from various sources, some originating from the sun and others coming from the atmosphere and so on. Initially thought to be massless, they are now believed to have a small mass, which differs from one flavour to another. Neutrino oscillations, in fact, would not be possible if they had no mass.
Reiterating the importance of neutrino research, Prof Naba Mondal of Tata Institute of Fundamental Research, director of the India-based Neutrino Observatory, said “We knew that they [Kajita and Mc Donald] would get the prize, it was only a question of when. It is time for celebrations in the neutrino community worldwide.”
According to Dr Mondal, there are several important questions about the neutrino which need to be investigated. One, the determination of absolute mass which Dr Mc Donald has alluded to; then, there is the sorting of the mass hierarchy among the three flavours, which the INO plans to work on, and the determination of whether neutrinos and antineutrinos behave in the same way, a clue for determining what is called CP violation.
The success of the experimental groups led by Dr. Kajita and Dr. Mc Donald in establishing through their experimental observations that on their way from the sun or the atmosphere to the earth, the neutrinos undergo a change from one flavour to another is what has fetched them the Nobel prize.
