Kajita, McDonald win Nobel physics prize

The Nobel Prize in Physics 2015 recognised Takaaki Kajita in Japan and Arthur McDonald in Canada for their contributions to experiments which demonstrated that neutrinos change identities.

In 1998, working at the Super-Kamiokande detector, a 50,000-tonne tank of highly purified water built at the bottom of an old zinc mine in central Japan, Kajita discovered that neutrinos seemed to change identities on their way from the Sun to Earth. Measurements conducted on Earth revealed that almost two thirds of the neutrinos that had to exist according to theoretical calculations were missing.

Takaaki Kajita and Arthur McDonald’s breakthrough was the discovery of a phenomenon called neutrino oscillation that has upended scientific thinking and promises to change understanding about the history and future fate of the cosmos.

“It is a discovery that will change the books in physics, so it is really major discovery”, Barbro Asman, a Nobel committee member and Professor of physics at Stockholm University, said.

The standard model had resisted all experimental challenges for two decades. In 2001, McDonald found that neutrinos coming from the sun also switched identities. But the numbers say that if they oscillate, they have mass. So something in the model is off. Although his favourite particles are neutral, his home province can’t be as we take pride and pleasure in the Nobel committee’s recognition of his work. After the photons, which make up light, they are the most abundant particle in the known universe.

McDonald told reporters winning the Nobel Prize was “a daunting experience”.

In 1988, Kajita announced the probability that neutrinos have mass, based on the data of “atmospheric neutrinos”, which emerge when cosmic rays from space collide with the Earth’s atmosphere. After getting his composure back, he stressed that many people had contributed to his work, and that there was much work still to do.”The universe where we live in is still full of unknowns”.

Neutrinos were a mystery since they were proposed by Wolfgang Pauli in 1930.

The revelation that neutrinos – the subatomic particles that are more numerous than any other in the universe except for particles of light – undergo a metamorphosis led to a second and shocking conclusion: that they have mass. Neutrinos are so small that about a billion neutrinos pass through a human thumb every second.

The winners will split the 8 million Swedish kronor (about United States dollars 960,000) prize money. And experiments are looking at whether there are other types of neutrinos beyond the three clearly observed.

The remaining four categories still to be awarded are Chemistry (Wednesday, 7 October), Peace (Friday, 9 October), Economics (Monday, 12 October) and Literature (date to be set later).