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Kajita and McDonald win Nobel physics prize for work on neutrinos

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Takaaki Kajita of Japan and Arthur McDonald of Canada have won the Nobel Prize in Physics for the discovery of neutrino oscillations.

The Royal Swedish Academy of Sciences said the two researchers had made key contributions to experiments showing that neutrinos change identities.  Kajita is director of the Institute for Cosmic Ray Research and professor at the University of Tokyo. McDonald is a professor emeritus at Queen’s University in Kingston, Canada.

“The discovery has changed our understanding of the innermost workings of matter and can prove crucial to our view of the universe,” the academy said.

The two physicists, conducting their experiments in two laboratories built inside disused mines lying deep underground in Japan and Canada, worked on two types of subatomic particles solar neutrinos and atmospheric neutrinos.

Neutrinos, the second most common subatomic particles in the entire cosmos after photons, were poorly understood by particle physicists. The inhabitants of “a hidden world”, they constantly bombard the Earth.

“Many neutrinos are created in reactions between cosmic radiation and the Earth’s atmosphere. Others are produced in nuclear reactions inside the Sun. Thousands of billions of neutrinos are streaming through our bodies each second. Hardly anything can stop them passing; neutrinos are nature’s most elusive elementary particles,” the Nobel committee said.

Research on Neutrinos :-

  • Physicists had for long considered neutrinos to be mass-less since compared to calculations made underground, up to two-thirds of neutrinos were found missing in measurements performed on the Earth’s surface.
  • But in 1998, Kajita was part of a team that announced the discovery that neutrinos have mass, using the Super-Kamiokande detector, located 1km underground in Japan. The scientists found that when they counted the relative number of the neutrinos in terms of distance and time, certain neutrinos called muon neutrinos were changing back and forth as they travelled through space or matter.
  • Just a year later, the research group in Canada led by McDonald showed that the neutrinos from the Sun were not disappearing on their way to Earth. Rather, they had been captured with a different identity when arriving to the Sudbury Neutrino Observatory, located 2.1km underground in Canada.
  • These two observations came to one conclusion—neutrinos change “flavours” (species in particle physics language) while travelling through space. And according to quantum theory, this is only possible if the particle in question has mass.
  • “A neutrino puzzle that physicists had wrestled with for decades had been resolved,” said the Nobel committee. McDonald stressed that the prize belonged to all the scientists who collaborated in this experiment.
  • Neutrinos are among the few fundamental particles that make up matter and have no electric charge. It is the global quest of scientists to understand more properties of neutrinos created in reactions between cosmic radiation and the Earth’s atmosphere and by nuclear reactions in the Sun.
  • The discovery of neutrinos having mass has far-reaching implications on the Standard Model of particle physics, which seeks to present an understanding of the building blocks of the universe and how they interact. “However, as it requires neutrinos to be mass-less, the new observations had clearly showed that the Standard Model cannot be the complete theory of the fundamental constituents of the universe,” said the Royal Swedish Academy for Sciences.
  • “We are all celebrating here as this is great news for the ‘neutrino community’. Neutrino oscillation discovery is now more than 16 years old and has had profound implications for particle physics,” said Naba K. Mondal, project director at India-based Neutrino Observatory (INO), which this year got approval from the Prime Minister’s Office. “The discovery that neutrinos have mass was the first indicator that there is physics beyond the Standard Model, and now there are so many revelations waiting to be discovered,” Mondal added.
  • Plans to build the INO 1.5km underground in Pottipuram in Bodi West hills, Tamil Nadu have faced protests from surrounding villages and activists who fear it will have an environmental impact. The Rs.1,500 crore project, cleared in January by the Prime Minister’s Office, is currently awaiting clearance from the Tamil Nadu Pollution Control Board.

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prize ceremony

prize ceremony

The winners will split the 8 million Swedish kronor (about $960,000) prize money. Each winner also gets a diploma and a gold medal at the prize ceremony on Dec. 10.

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