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European physicists have new evidence to support their claim that subatomic particles travelled faster than light, in violation of a scientific dogma that has stood since Einstein published his theory of relativity.
Their original publication in September provoked scepticism. So researchers carried out new experiments to rule out possible sources of error – shooting beams of neutrinos 730km (454 miles) from Cern, the European nuclear physics centre near Geneva, to a detector in the Gran Sasso underground laboratory in central Italy.
Dario Autiero, a leader of the Opera project at Gran Sasso, said results being presented on Friday, and reanalysis of earlier data, eliminated several possible sources of error.
The researchers changed their procedure to send neutrinos in extremely short bursts, lasting just three nanoseconds, instead of the longer pulses transmitted previously. This has enabled them to pin down the neutrinos’ time of flight more accurately than before.
“Many people were having doubts about our statistical analysis,” said Dr Autiero. “Now the statistical analysis is trivial.”
The neutrinos arrived at Gran Sasso 60 nanoseconds sooner than they would at the speed of light (almost 300,000km/s). Although the particles were exceeding the speed of light by just 20 parts per million, even such a small excess would destroy the theoretical foundations of physics.
More experiments will take place next year to improve further the precision of the measurements. But Dr Autiero and his 160 colleagues from around the world taking part in the Opera project accept that the result must be confirmed independently by experiments elsewhere, if it is to win scientific acceptance.
The main cross-checking is taking place at Fermilab near Chicago, where an experiment called Minos is shooting neutrinos a similar distance to an underground detector in Minnesota.
Minos scientists found a hint in 2007 that the particles might be travelling faster than light but were not convinced that it was statistically significant.
“We are going back to our own original data and improving our systems, for example by upgrading our atomic clocks to give better time measurements,” said Joe Walding, a Minos researcher. “In four or five months, Minos should be able to say whether Opera was on the right path and within a year say whether the [faster than light] result was valid.”
Meanwhile, theoreticians are having a field day thinking of explanations for neutrinos breaking the light speed limit, for example by taking short-cuts through hidden extra dimensions.
But the Opera scientists themselves are resisting such speculation for the moment. “We want to concentrate on producing good data,” said Dr Autiero.