New Delhi, Nov. 18: An experimental observation that seems to violate a cosmic speed limit imposed by Albert Einstein’s special theory of relativity has survived a second more rigorous set of tests, two months after physicists first revealed their stunning results.

Physicists said today their new tests have confirmed their earlier observations of subatomic particles called neutrinos flitting from a laboratory in central Europe to the Gran Sasso mountain in Italy faster than the speed of light.

The neutrinos produced at the underground laboratory of the European Organisation for Nuclear Research, or CERN, near Geneva arrived at the Gran Sasso laboratory about 62 nanoseconds (billionths of a second) ahead of light.

Scientists at the Italian Institute of Nuclear Physics said the new tests seem to exclude part of the potential systematic effects that could have influenced the earlier measurements of faster-than-light neutrinos.

“A measurement so delicate and carrying a profound implication on physics requires an extraordinary level of scrutiny,” Fernando Ferroni, the president of the Italian institute, said in a statement. “The positive outcome of the test makes us more confident in the result,” he said, but cautioned that clinching evidence would emerge only when the experiment is repeated elsewhere in the world.

Einstein’s special theory of relativity, which has so far passed every experimental test since it was proposed more than a century ago, dictates that nothing can travel faster than the speed of light — 299,792km per second.

“We still have a wait ahead of us — maybe a long wait,” said Amitava Raychaudhuri, the Palit Professor of physics at the University of Calcutta, a theoretical physicist who had published a paper a decade ago suggesting that neutrinos may deviate from relativity.

“It’s still early to speculate about whether and how the special theory of relativity will need to be modified to account for these observations. We’ll need to study the neutrinos and it may take years for a theory to emerge — if at all a modified theory is required.”

But Raychaudhuri and other physicists believe the results announced today are significant because they seem to address key questions that experimental physicists had raised after the first announcement this September. One of these questions relates to the accuracy of synchronisation of clocks at the two places (Geneva and Gran Sasso) which is crucial for the accuracy of speed measurements.

The new tests have bolstered physicists’ confidence in their earlier measurements because they have used neutrinos in three nanosecond bunches spaced apart by 524 nanoseconds. This protocol permits more accurate measurements of their velocity, but at the price of a lower intensity of the beam, which translates into fewer events to observe compared to the earlier measurements.

In the results announced in September, physicists were able to study 15,000 neutrinos travelling the 730km from CERN to Gran Sasso. In the new results with higher accuracy, physicists could study “only 20 clean events”.

“The statistics thus is weaker than with the earlier observations — nevertheless this adds confidence to the results,” Raychaudhuri told The Telegraph. Physicists believe neutrinos produced in Fermilab in the US should be used to validate these observations.

Even the physicists involved in the experiments have declined to speculate on theoretical interpretation of these results, pending independent confirmation elsewhere.

“Despite the large significance of the measurement reported here... the potential great impact of the result motivates the continuation of our studies in order to investigate possible unknown systematic effects that could explain the observed anomaly,” they said in a paper.