The amazing disappearing antineutrino

[n2doc]

A revised calculation suggests that around 3% of particles have gone missing from nuclear reactor experiments.

Eugenie Samuel Reich


Measurements from the Sudbury Neutrino Observatory in Canada were thought to have settled the mysteries of neutrinos - but new calculations have raised new questions.Roy Kaltschmidt / Lawrence Berkeley Nat'l Lab

Neutrinos have long perplexed physicists with their uncanny ability to evade detection, with as many as two-thirds of the ghostly particles apparently going missing en route from the Sun to Earth. Now a refined version of an old calculation is causing a stir by suggesting that researchers have also systematically underestimated the number of the particles' antimatter partners — antineutrinos — produced by nuclear reactor experiments.

The deficit could be caused by the antineutrinos turning into so-called 'sterile antineutrinos', which can't be directly detected, and which would be clear evidence for effects beyond the standard model of particle physics.

In the 1960s, physicist Ray Davis, working deep underground in the Homestake gold mine in South Dakota, found that the flux of solar neutrinos hitting Earth was a third of that predicted by calculations of the nuclear reactions in the Sun by theorist John Bahcall. Davis later received a Nobel prize for his contributions to neutrino astrophysics. That puzzle was considered solved in 2001, when the Sudbury Neutrino Observatory (SNO) in Canada found the missing two-thirds through an alternative means of detection. The SNO's results were taken as evidence that neutrinos have a mass, which allows them to oscillate between three flavours: electron, muon and tau. Davis had only detected the electron neutrinos.

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http://www.nature.com/news/2011/110401/full/news.2011.202.html