The OPERA detector in Gran Sasso, Italy, is designed to detect neutrinos generated from protons 730 kilometres away at CERN, near the French-Swiss border. OPERA

Scientists who recently reported subatomic particles moving faster than light are testing a revised experimental procedure to see if it will generate the same astonishing result as before.

In September, scientists at the European Organization for Nuclear Research, also known as CERN, announced that an international physics collaboration called OPERA had clocked particles called neutrinos travelling faster than light —something that is impossible according to Einstein's 1905 special theory of relativity, which provides the basis for most of modern physics.

The scientists said they were very surprised by the finding, but were unable to trace it to an error, so they were asking others to scrutinize it carefully and independently verify the measurements.

The announcement was greeted by skepticism from many physicists, who said a very high standard of proof is needed for such an extraordinary result, which was more likely the result of an undiscovered error.

However, scientists from the OPERA collaboration announced at a particle physics conference last week in Nagoya that they had recently begun running the experiment slightly differently, reported Matt Strassler, a theoretical physics professor at Rutgers University in Piscataway, N.J., on his blog. Results were expected in a few weeks.

Sergio Bertolucci , director of research at CERN, confirmed that information to BBC News late last week.

Originally, the neutrinos were generated from a beam of protons in an experiment at CERN, near Geneva at the border between France and Switzerland, in a pulse lasting 10 millionths of a second — a long time on the scale of the measurements. The beam of neutrinos travelled to Gran Sasso in Italy, 730 kilometres away, where their average arrival time was measured and compared to their average departure time and the distance to calculate their average speed.

The new measurements involve the release of protons in pulses lasting just one or two nanoseconds or 5,000 to 10,000 times shorter, with a long separation between each pulse.

That would allow researchers to match each neutrino detection at Gran Sasso with a very precisely timed proton pulse from CERN instead of having to work with averages.

'Fine tuning'

"We are not really repeating the experiment in the strict sense as beams are going all the time to Gran Sasso," said the CERN press office in a statement to CBC News Monday confirming the changes to the experiment.

"It is just basically fine tuning.… There is not much more to say."

Strassler explained on his blog that the scientists had been reluctant to make the change to their experiment initially because it greatly reduces the production of neutrinos, which has a negative impact on their other experiments.

"But apparently the concerns raised by the community have been strong enough to prompt OPERA to request that the CERN neutrino beam operators send them short pulses," wrote Strassler, who himself had been a critic of the original experiment.

"This is very good news."