The news that the faster-than-light neutrino results announced to such widespread interest by the OPERA collaboration have now been explained has been spreading irresistibly around the Internet. But the brief piece in ScienceInsider that broke the news was stretching a point with a lead reading “Error Undoes Faster-Then-Light Neutrino Results.” For when you read the story, you see that a fiber optic cable connection is a possible culprit, though as yet an unconfirmed one.
Sean Carroll (Caltech) blogged on Cosmic Variance that while he wanted to pass the news along, he was reserving judgment until a better-sourced statement came to hand. I’ve thought since the beginning that a systematic error would explain the ‘FTL neutrino’ story, but I still was waiting for something with more meat on it than the ScienceInsider news. It came later in the day with an official CERN news release, and this certainly bears quoting:
The OPERA collaboration has informed its funding agencies and host laboratories that it has identified two possible effects that could have an influence on its neutrino timing measurement. These both require further tests with a short pulsed beam.
So we have not just one but two possibilities here, both with ramifications for the neutrino timing measurements and both needing further testing. And let’s go on with the news release:
If confirmed, one would increase the size of the measured effect, the other would diminish it. The first possible effect concerns an oscillator used to provide the time stamps for GPS synchronizations. It could have led to an overestimate of the neutrino’s time of flight. The second concerns the optical fibre connector that brings the external GPS signal to the OPERA master clock, which may not have been functioning correctly when the measurements were taken. If this is the case, it could have led to an underestimate of the time of flight of the neutrinos. The potential extent of these two effects is being studied by the OPERA collaboration. New measurements with short pulsed beams are scheduled for May.
Image: Detectors of the OPERA (Oscillation Project with Emulsion-tRacking Apparatus) experiment at the Italian Gran Sasso underground laboratory. Credit: CERN/AFP/Getty Images.
We may well be closing on an explanation for a result many scientists had found inconceivable. Here’s a BBC story on the possibility of trouble with the oscillator and/or an issue with the optical fiber connection. We learn here that a new measurement of the neutrino velocity will be taken in 2012, taking advantage of international facilities ranging from CERN and the Gran Sasso laboratory in Italy to Fermilab and the Japanese T2K. The story quotes Alfons Weber (Oxford University), who is working on the Minos effort to study the neutrino measurements at Fermilab:
“I can say that Minos will quite definitely go ahead… We’ve already installed most of the equipment we need to make an accurate measurement. Even if Opera now publish that ‘yes, everything is fine’, we still want to make sure that we come up with a consistent, independent measurement, and I assume that the other experiments will go forward with this as well.”
So this is where we are: An anomalous and extremely controversial result is being subjected to a variety of tests to find out what caused it. If I were a betting man, I would put a great deal of money on the proposition that the FTL results will eventually be traced down to something as mundane as the optical fiber connector that is now the subject of so much attention. But we’ll know that when it happens, and this is the way science is supposed to work. OPERA conducted numerous measurements over a three year period before announcing the FTL result. Let’s now give the further work time to sort out what really happened so we can put this issue to rest.