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Once Again, Physicists Debunk Faster-Than-Light Neutrinos

Enough already. Five different teams of physicists have now independently verified that elusive subatomic particles called neutrinos do not travel faster than light. New results, announced today in Japan, contradict those announced last September by a 170-member crew working with the OPERA particle detector in Italy's subterranean Gran Sasso National Laboratory. The OPERA team made headlines after they suggested neutrinos traveled 0.002% faster than light, thus violating Einstein's theory of special relativity. The OPERA results were debunked months ago, however. So instead of the nail in the coffin of faster-than-light neutrinos, the new suite of results is more like the sod planted atop their grave.

The OPERA team had timed neutrinos fired through Earth from the European particle physics laboratory, CERN, near Geneva, Switzerland, and found that they made the 730-kilometer trip to Gran Sasso 60 nanosecond faster than they would traveling at light speed. But in February, the OPERA team also discovered that a loose fiber optic cable had introduced a delay in their timing system that explained the effect. A month later, researchers working with the ICARUS particle detector, also housed in Gran Sasso, measured the speed of neutrinos fired from CERN and found that they travel at light speed, as predicted. By that point, most physicists deemed faster-than-light neutrinos really most sincerely dead. Some OPERA team members thought the whole episode had besmirched the collaboration's reputation, and in March, two of the team's elected leaders lost a vote of no confidence and tendered their resignations.

Nevertheless, researchers kept at their efforts to test the result. Gran Sasso houses four particle detectors capable of timing neutrinos fired from CERN: OPERA, ICARUS, BOREXINO, and LVD. All four have now found that the neutrino's speed is consistent with the speed of light, as Sergio Bertolucci, research director at CERN, reported at the 25th International Conference on Neutrino Physics and Astrophysics in Kyoto, Japan. The speed of neutrinos was also measured by researchers working with the MINOS experiment, which shoots neutrinos 735 kilometers from Fermi National Accelerator Laboratory (Fermilab) in Batavia, Illinois, to a detector in the Soudan mine in northern Minnesota. The MINOS team has also found that neutrinos travel at light speed, as Fermilab's Phil Adamson reported at the meeting.

So the chorus has sung and the final curtain has fallen on the faster-than-light neutrino saga. "The story captured the public imagination, and has given people the opportunity to see the scientific method in action—an unexpected result was put up for scrutiny, thoroughly investigated and resolved in part thanks to collaboration between normally competing experiments," Bertolucci says in a CERN press release. "That's how science moves forward." Fair enough. But can we move on now?