Puzzling results from Cern, home of the Large Hadron Collider, have confounded physicists because subatomic particles seem to have beaten the speed of light.
Neutrinos sent through the ground from Cern toward the Gran Sasso laboratory 732km away in Italy seemed to show up a tiny fraction of a second early.
The results - which threaten to upend a century of physics - were put online for scrutiny by other scientists.
In the meantime, the group says it is being very cautious about its claims.
They will be discussing the result in detail in a conference at Cern on Friday afternoon, which can be viewed online.
"We tried to find all possible explanations for this," said report author Antonio Ereditato of the Opera collaboration.
"We wanted to find a mistake - trivial mistakes, more complicated mistakes, or nasty effects - and we didn't," he told BBC News.
"When you don't find anything, then you say 'Well, now I'm forced to go out and ask the community to scrutinise this.'"