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Neutrino Update: New Doubts

Research conducted during the weeks after the recent faster-than-light neutrino observation has contradicted the original finding. When neutrinos travel faster than light, there should be characteristic radiation left in their wake according to new research. Not seeing this radiation in past results from the same beam used in the original experiment, an Italian team from the same laboratory has cast doubt on the existence of superluminal particles.

A neutrino detector buried deep underground in Ontario, CA. Image courtesy A.B. McDonald/The Sudbury Neutrino Observatory Institute.

These results out of Italy represent an analysis of 2010 data through the lens of theoretical research carried out in October. Two researchers at Boston University (BU) published a paper in Physical Review Letters suggesting that neutrino beams should emit radiation in a process analogous to Cherenkov radiation.

Cherenkov radiation—commonly seen in nuclear reactors and particle accelerators—occurs when particles travel faster than light would in a certain medium. In water, for instance, light travels about 3/4 its speed in a vacuum, allowing particles to actually travel faster than light. Eerie blue light emitted in nuclear reactors actually stems from the light cone produced by Cherenkov radiation.

Similarly, researchers expect that particles traveling faster than the speed of light in a vacuum would exhibit similar behavior. But an analysis of data from the ICARUS experiment at the Gran Sasso laboratory didn't turn up the expected radiation.

Although the team was looking at data coming from the same neutrino beams from CERN, the energy spectrum looked like those of traditional neutrinos that obey the universal speed limit. Superluminal neutrinos should produce electron-positron pairs and gamma rays, but no such radiation was found. Consequently, the authors concluded that, "Our results therefore refute a superluminal interpretation of the OPERA result," according to the theoretical research done by the BU researchers.

On the Science 2.0 blogging site, physicist Tommaso Dorigo who works on the CMS experiment at Cern agreed strongly with the new results: "As for me, I can chuckle and archive this umpteenth 6-sigma anomaly in the Zoo of wannabe new physics results. Physics is hard, folks–you can't expect to be dealt a straight flush all of the times."

The question of superluminal neutrinos, however, seems to be far from settled. Despite earlier headlines like "Second experiment confirms faster-than-light particles," only time will tell if speedy neutrinos will withstand further scrutiny. New experiments from independent neutrino beams in Japan and the United States should clear up some of the current uncertainty.


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