Superfast neutrino claim takes another beating

Superluminal neutrinos are slowing fast. Last September, a preliminary but electrifying result suggested these ghostly subatomic particles might travel faster than light. Now a second experiment, ICARUS - based in the same lab in the Gran Sasso mountain, Italy, as the original one, OPERA - has measured the particles' flight time and found that they seem to fly at light speed after all.

The neutrinos that seemed to fly faster than light travelled to Gran Sasso from a particle accelerator at CERN near Geneva, Switzerland. A re-run of the experiment with an improved neutrino beam from CERN gave the same result a few months later.

The result flew in the face of Einstein's well-tested theory of special relativity, which holds that nothing can accelerate past the speed of light. The announcement triggered a torrent of speculation about what exotic physics could account for the result: extra dimensions? Tachyons? Extra subatomic particles not yet discovered?

Most physicists remained sceptical, though. Theoretical problems with the result piled up quickly, including a suggestion from Andrew Cohen and Nobel laureate Sheldon Glashow, both at Boston University, that neutrinos flying faster than light should emit radiation analogous to an electromagnetic sonic boom.