Physicists explain technical glitches behind those faster-than-light neutrinos

Yesterday, rumors were circulating that last year's faster-than-light neutrino results had been undone by a simple mechanical mishap: one of the fiber optic cables connecting a GPS unit to a computer may have been loose.

At the time, anonymous sources "familiar with the experiment" were the best anyone could come up with in the way of an authoritative reference, but late last night, the OPERA Collaboration (the team of researchers that first announced the FTL-findings) issued a formal statement.

The statement confirmed two things:

1) Yes, the team's FTL-findings have recently been called into question
2) Yes, a fiber optic cable may well be the culprit behind the experiment's puzzling results

But according to OPERA physicists, there may be a second hangup. The statement reads in full:

Physicists explain technical glitches behind those faster-than-light neutrinos

The OPERA Collaboration, by continuing its campaign of verifications on the neutrino velocity measurement, has identified two issues that could significantly affect the reported result. The first one is linked to the oscillator used to produce the events time-stamps in between the GPS synchronizations. The second point is related to the connection of the optical fiber bringing the external GPS signal to the OPERA master clock.

These two issues can modify the neutrino time of flight in opposite directions. While continuing our investigations, in order to unambiguously quantify the effect on the observed result, the Collaboration is looking forward to performing a new measurement of the neutrino velocity as soon as a new bunched beam will be available in 2012. An extensive report on the above mentioned verifications and results will be shortly made available to the scientific committees and agencies.

Did you catch that? Both of the proposed sources of error are related to the experiment's use of GPS, but each one would skew the neutrinos' measured flight time in a different direction; the issue with the oscillator would actually increase the size of the measured effect, while the error associated with the fiber optic cable would diminish it. So what's the net effect?

Reuters is reporting that the loose fiber optic cable appears to "be more significant" than the problems posed by the oscillator, but it will still be a few months until we know for sure. CERN has also weighed in on the cable fiasco with a release that echoes the points addressed in the OPERA statement, but adds that "new measurements with short pulsed beams are scheduled for May."

So whether it's a cable, an oscillator, or something else entirely, it sounds like we'll have to wait a few months before we know the net effect of the two opposing sources of error. Nevertheless, it's nice to know these physicists actually have some tangible leads to follow — even if it does mean debunking what would have been the biggest paradigm shift in recent history.

[CERN | Nature | Reuters]
Neutrino tracks via CERN; OPERA detecter via OPERA