Neutrino experiment repeat at Cern finds same result
Neutrinos travel through 700km of rock before reaching Gran Sasso's underground laboratories The collaboration behind the finding in September that neutrinos may travel faster than light has carried out an improved version of their experiment - and found the same result.
If confirmed by other experiments, the find could undermine one of the basic principles of modern physics.Critics of the first report had said that the long bunches of neutrinos used could introduce an error into the test.
The new work, posted to the Arxiv repository, used much shorter bunches.
It has been submitted to the Journal of High Energy Physics, but has not yet been reviewed by the scientific community.
The experiments have been carried out by the Opera collaboration - short for Oscillation Project with Emulsion-tRacking Apparatus.
It hinges on sending bunches of neutrinos created at the Cern facility (actually produced as decays within a long bunch of protons produced at Cern) through 730km of rock to a giant detector at the Gran Sasso laboratory in Italy.
The initial series of experiments, comprising 16,000 separate measurements spread out over three years, found that the neutrinos arrives 60 billionths of a second faster than light would have, travelling unimpeded over the same distance.
The idea that nothing can exceed the speed of light in a vacuum forms a cornerstone in physics - first laid out by James Clerk Maxwell and later incorporated into Albert Einstein's theory of special relativity.
Initial analysis of the work by the wider scientific community argued that the relatively long bunches of neutrinos could introduce a significant error into the measurement.
Those bunches lasted 10 millionths of a second - 160 times longer than the discrepancy the team initially reported in the neutrinos' travel time.
To address that, scientists at Cern adjusted the way in which the proton beams were produced, resulting in bunches just three billionths of a second long, so the Opera collaboration could repeat the measurements.
'Profound implication' The first announcement of evidently faster-than-light neutrinos caused a stir world-wide; the Opera collaboration is very aware of its implications if eventually proved correct.
Evidence of neutrinos shows up in "bubble chambers", a now outdated particle physics tool
The error in the length of the bunches, however, is just the largest among many potential sources of uncertainty in the measurement, all of which must now be addressed in turn."A measurement so delicate and carrying a profound implication on physics requires an extraordinary level of scrutiny," said Fernando Ferroni, president of Italian Institute for Nuclear Physics in a statement.
"The experiment Opera, thanks to a specially adapted Cern beam, has made an important test of consistency of its result. The positive outcome of the test makes us more confident in the result, although a final word can only be said by analogous measurements performed elsewhere in the world."
Those measurements may be much longer in coming, as only a few facilities worldwide have the detectors needed to catch the notoriously flighty neutrinos - which interact with matter so rarely as to have earned the nickname "ghost particles".
Next year, teams working on two other experiments at Gran Sasso experiments - Borexino and Icarus - will begin independent cross-checks of Opera's results.
The US Minos experiment and Japan's T2K experiment will also test the observations. It is likely to be several months before they report back.
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