How Many Neutrinos Does It Take to Screw Up Einstein?
WIRED
By Adam Mann
November 18, 2011

Image: OPERA collaboration

Results from a second experiment uphold the observation that neutrinos are moving faster than the speed of light. The OPERA collaboration, which first reported the superluminal neutrinos in September, has rerun the experiment and detected 20 new neutrinos breaking Einstein’s theoretical limit.

The findings are heartening to anyone hoping to see a major physics revolution in their lifetime. But scientists, as ever, are being cautious, and it will take an independent replication of the results by another team to even begin convincing many of them.

“This eliminates one major class of systematic errors, and it’s impressive for the OPERA team to have mounted in a short period of time,” said physicist Robert Plunkett of Fermilab National Laboratory in Batavia, Illinois. “However, it doesn’t mean that there isn’t an error somewhere else in their system.”

Neutrinos are subatomic particles with hardly any mass that are able to fly through most matter as if it weren’t there. Despite their negligible mass, if they were somehow able to exceed the speed-of-light limit set by Einstein’s theory of special relativity, it would present a major head-scratcher to modern physicists.

The OPERA team’s detector at Gran Sasso National Laboratory in Italy had previously detected neutrinos produced in bunches at CERN arriving 60 nanoseconds earlier than light speed would allow. The tricky part is that these bunches took a good length of time to produce — much longer than 60 nanoseconds — so the researchers had to be careful with their analysis. If they thought a neutrino was coming from the start of the bunch when it was actually coming from the end, then that neutrino would not actually be moving faster than light.

In their first experiment, the OPERA team used statistical analysis to show this situation was unlikely, but other scientists were not completely persuaded. The new experiment produced neutrinos in bunches over just three nanoseconds, far shorter than the faster-than-light anomaly. The results were the same: Neutrinos arrived 60 nanoseconds quicker than the speed of light. The findings were robust enough that members of the OPERA collaboration who had refused to sign on to the first paper were now willing to put their name on the new one.

But a great deal of scrutiny remains.

“I can now say that the probability of the result being correct has increased from 1 in a million to one in 100 thousand,” wrote physicist Philip Gibbs on the viXra log (though he stressed that those numbers were merely illustrative and not actual calculated values).

Tommaso Dorigo, a physicist at CERN, noted on his blog that there are still other possible sources of error. For instance, the OPERA collaboration’s clock might not have a fine enough resolution to determine exactly when the neutrinos arrived. “The measurement therefore is only a ‘partial’ confirmation of the earlier result: It is consistent with it, but could be just as wrong as the other,” he wrote.

Ultimately, the only thing that would convince many in the field is if another team upholds the findings in an independent experiment. Plunkett, co-spokesperson for the Main Injector Neutrino Oscillation Search (MINOS) experiment at Fermilab, says that his collaboration expects to have results checking the OPERA findings in the spring of 2012

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