document: The Amazing Disappearing Neutrino By Eugenie Samuel Reich of Nature magazine 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 ca n'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 -LRB- SNO -RRB- 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 flavors : electron , muon and tau . Davis had only detected the electron neutrinos . Experiments that measure the rate of antineutrino production from the decay of uranium and plutonium isotopes have so far produced results roughly consistent with this theory . But the revised calculation accepted this week by Physical Review D suggests that it 's not the whole story . While waiting for the Double Chooz neutrino experiment in France to become fully operational , Thierry Lasserre and his colleagues at the French atomic energy commission -LRB- CEA -RRB- in Saclay set out to check predictions of the rate of antineutrino production by nuclear reactors . They repeated a calculation first done in the 1980s by Klaus Schreckenbach at the Technical University of Munich , using more modern techniques that allowed them to be much more precise . Their new estimate of the rate of production is around 3 % more than previously predicted . This means that several generations of neutrino and antineutrino experiments have unknowingly missed a small fraction of the particles . '' `` It was completely a surprise for us , '' '' says Lasserre . Double Chooz consists of two detectors measuring the flux of antineutrinos produced by the Chooz nuclear power plant in the French Ardennes , one detector about 400 meters away from the plant and the other 1 kilometer away . The far detector became operational this year . Stefan Schönert , a neutrino physicist at the Technical University of Munich , says the calculation is solid , and has been checked with Schreckenbach . '' `` They can reproduce each other 's results . There 's no way around this result . It 's very solid . '' '' Art McDonald of Queen 's University in Kingston , Canada and the SNO says that people have to look carefully at the calculation , which may itself have a systematic error . But , he adds , '' `` there 's no doubt it would have significance as a physics result if it can be shown with more accuracy . '' '' The result may be pointing to evidence of neutrinos and antineutrinos oscillating into a fourth kind of neutrino or antineutrino , a so-called ` sterile ' version that does n't interact with ordinary matter , says Carlo Giunti , a physicist at the University of Turin in Italy . Other experiments have previously seen evidence for sterile particles , including the Liquid Scintillator Neutrino Detector at Los Alamos National Laboratory in New Mexico and the Mini Booster Neutrino Experiment , or MiniBooNE , at Fermilab in Batavia , Illinois , and the search to confirm their existence is a hot area of physics . Giunti says that the magnitude of the anomaly uncovered by Lasserre is not statistically significant on its own , but that it points promisingly in the same direction as another anomaly found by the SAGE collaboration , which studied neutrinos from a radioactive source at the Baksan Neutrino Observatory in the Caucasus in 2005 . '' `` Before this , there used to be a contradiction between -LSB- reactor and radioactive source -RSB- experiments but now they are in agreement , '' '' says Giunti . Schönert says that one key experiment everyone is waiting for is a measurement showing that the rate of disappearance of antineutrinos from a source increases with the distance from it . '' `` This would be the smoking gun , '' '' he says . This article is reproduced with permission from the magazine Nature . The article was first published on April 1 , 2011 .
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