In results announced last month, neutrinos sent through the ground from Geneva, Switzerland, home of Cern and the Large Hadron Collider, toward a laboratory 455 miles away in Italy seemed to arrive a tiny fraction of a second earlier than light would have.
Scientists in charge of the so-called Opera experiment said they would repeat it with some changes to rule out any possible sources of error before submitting the result, and its astonishing implications, for publication.
Much of modern physics is founded on the foundation of an ultimate universal speed limit, that nothing can travel faster than light.
Many scientists have said they believe some "systematic" error in the experiment is giving a false and impossible result.
So the experimenters will run it again, Cern officials said.
"In the last few days we have started to send a different time structure of the beam to [Italy]," Sergio Bertolucci, the director of research at Cern, told BBC News.
"This will allow Opera to repeat the measurement, removing some of the possible systematics."