More superluminal neutrinos

20 November 2011
Posted by Dave Ansell.

In September results indicating that neutrinos travel faster than the speed of light were released, this week the same group has released further data.

The experiment is spread out between CERN near Geneva and a neutrino detector near Rome called OPERA over 700km away. In CERN groups of protons flying around the LHC ring are redirected down an alternative route and crash into a lump of graphite. This produces a variety of particles but includes a large number of particles called mesons, which have a very short lifetime, they fly down a kilometre long tube where some of them decay to form an electron and a neutrino.        

These neutrinos hardly interact with matter, so they easily pass through the 700km of solid rock, and then a tiny proportion of them interact with plates of lead in the OPERA detector inside a mountain in Italy, producing a signal which can be detected.

The experiment was designed to investigate whether neutrinos change over time, and to measure how much slower than the speed of light they travel, which would give information about their mass and behaviour.

The very surprising result was that they appeared to be travelling the distance about 60ns faster than the speed of light, travelling about 2.5 parts in 100 000 faster. This would indicate fundamentally new physics and extraordinary claims require extraordinary evidence, and they have had a variety of suggestions from the community on how they could improve their results.

So they have gone away and tried to improve the resolution of their results. They have tried to get a more accurate measurement of the relative positions of the two facilities as the time difference could be explained by an error of position of about 180m. They have also made the bunches of protons that create the neutrinos shorter which makes it easier to measure the exact time they arrive. And seem to give the same result.

This is interesting but there is still a lot of evidence to overcome, for example in 1987 there was a supernova in the large magellanic cloud which produced both light and neutrinos and they both arrived here a few hours apart where as with the difference of speeds they were finding at CERN you would expect a difference of a couple of years. These neutrinos were lower energy than the ones produced in this experiment so it is possible they behave differently, but without independent confirmation I wouldn't start ordering your faster than light spacedrives yet.

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