New Delhi, Sept. 23: Physicists today announced having observed subatomic particles called neutrinos travel faster than light, a tantalising result some have dubbed unbelievable as it breaches a cosmic speed limit imposed by Albert Einstein’s relativity theory.

High-precision measurements of the speed of the neutrinos zipping 730km between two laboratories in Europe suggest that the particles travelled at a velocity 20 parts per million above the speed of light, an international team of physicists said.

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

The physicists have released the results of their experiments at a seminar in Geneva and through a web-based archive of research papers. They have said that they have deliberately not attempted any theoretical interpretation of the results.

“When an experiment finds an apparently unbelievable result and can find no artefact of (experimental) measurement(s) to account for it, it is normal procedure to invite broader scrutiny,” said Sergio Bertolucci, research director at the European Organisation for Nuclear Research, or CERN, a particle accelerator laboratory in Geneva, Switzerland.

The neutrinos were produced at CERN and observed at the underground Gran Sasso laboratory in Italy.

The results are based on the study of 15,000 neutrinos picked up at Gran Sasso during 2009, 2010 and 2011. The researchers say there is a need to further investigate the possibility that some unknown experimental effects might explain the puzzling results.

“The principle of relativity had until now never been tested on neutrinos at this precision,” said Amitava Raychaudhuri, a physicist at the University of Calcutta, who had 10 years ago published a paper suggesting neutrinos may deviate from the rules of relativity.

“This idea has been around for more than a decade,” Raychaudhuri told The Telegraph.

A leading American physicist and Nobel laureate Sheldon Glashow had proposed in the late 1990s that neutrinos violating relativity might explain another puzzling antic these tiny subatomic particles have been seen to perform. Neutrinos come in three types, and it appears they can metamorphose from one type into another, like a cricket ball changing colour as it travels from the bowler to batsman.

Any violation of relativity by neutrinos may force a rethink of a fundamental theory of physics called the Standard Model that explains all known subatomic particles.

“Relativity appears to work on all the other particles. If the neutrino behaves in such a crazy fashion, we’ll have to modify the Standard Model,” Raychaudhuri said.

The neutrinos, produced at CERN by accelerating and shooting protons at a graphite target, travelled ghost-like through the ground and reached a neutrino detector named OPERA at Gran Sasso.

OPERA scientists at Gran Sasso have described their results as a “complete surprise”.

“After many months of studies and cross-checks, we have not found any instrumental effect that could explain the result of the measurement,” said Antonio Ereditato, a physicist at the University of Bern and spokesperson for the experiment.

The new findings are likely to accelerate efforts to repeat the experiments elsewhere.

“It looks like this team has taken great care and measured the distances very carefully — but independent validation of the results at a separate site will be crucial,” said Naba Mondal, a physicist at the Tata Institute of Fundamental Research, Mumbai, who is part of a team leading an Indian proposal to build a neutrino observatory in southern India.