Puzzling results from Cern, home of the LHC, have confounded physicists - because it appears subatomic particles have exceeded the speed of light.
Neutrinos sent through the ground from Cern toward the Gran Sasso laboratory 732km away seemed to show up a few billionths of a second early.
The results will soon be online to draw closer scrutiny to a result that, if true, would upend a century of physics.
The lab's research director called it "an apparently unbelievable result".
The speed of light is the Universe's ultimate speed limit, and the entirety of modern physics - as laid out in part by Albert Einstein in his theory of relativity - depends on the idea that nothing can exceed it.
Thousands of experiments have been undertaken to measure it ever more precisely, and no result has ever spotted a particle breaking the limit.
But Antonio Ereditato of the Opera collaboration and his colleagues have been carrying out an experiment for the last three years that seems to suggest neutrinos have done just that.
Neutrinos come in a number of types, and have recently been seen to switch spontaneously from one type to another.
Dr Ereditato and his colleagues prepare a beam of just one type, muon neutrinos, sending them from Cern to an underground laboratory at Gran Sasso in Italy to see how many show up as a different type, tau neutrinos.
In the course of doing the experiments, the researchers noticed that the particles showed up 60 billionths of a second sooner than light would over the same distance.
The team measured the travel times of neutrino bunches some 15,000 times, and have reached a level of statistical significance that in scientific circles would count as a formal discovery.
But because the result is so unexpected and would wreak such havoc with our understanding of the Universe, the group is being particularly cautious. They have opted to put a report of their measurements online to subject them to wider scrutiny, and will hold a seminar at Cern on Friday to discuss the result.