Results from the first experiment in September suggested neutrinos can exceed light speed, but the results were met with considerable skepticism as the finding, if proved, would have upended Einstein's theory of relativity, a cornerstone of modern physics theory.
A repeat run of the experiment by a different group of researchers at the same laboratory has now clocked neutrinos traveling at precisely light speed, the BBC reported Friday.
The repeat experiment used 600 tons of liquid argon to detect the arrival of neutrinos sent through 450 miles of rock from the Cern laboratory in Switzerland to the Gran Sasso underground laboratory in Italy.
The results showed neutrinos do travel at the same speed as light, researchers said.
"We are completely compatible with the speed of light that we learn at school," said Sandro Centro, a spokesman for the new experiment team.
Subsequent reviews of the initial experiment have suggested instrumentation errors may have led to the faster-than-light-speed result.
"I think they were a little bit in a hurry to publish something that was astonishing, and at the end of the day it was a wrong measurement," Centro said of the original experimenters.