In case you haven’t yet heard (check my previous post from this morning), neutrinos traveling 730 kilometers from the CERN laboratory to the Gran Sasso laboratory do arrive at the time Einstein’s special relativity predicts they would.
Of course (as the press mostly seems to forget) we knew that. We knew it because
- ICARUS already made the measurement of timing, based on October 2011 data, and presented their result in March. That was a refutation of OPERA’s original result. I wrote about that here.
- OPERA itself preliminarily confirmed (quietly and without fanfare, just before the two leaders of the experiment stepped down from their leadership positions) that the two problems it identified in December and reported on in public in February did appear to be of the right size and shape to cause its false results for both OPERA-1 and OPERA-2 (the 2008-2011 long-pulse measurement and the October 2011 short-pulse measurement.)
So the news from the Neutrino 2012 conference in Kyoto, on new data from May 2012 taken by OPERA and three nearby experiments, is no surprise to anyone who was paying attention back in March and early April; it’s exactly what we were expecting.
One thing that almost no one is reporting, as far as I can tell, is that CERN’s research director Sergio Bertolucci did not give the first talk on neutrino speeds in Kyoto. That talk was given by Marcos Dracos, of OPERA. Dracos presented both OPERA’s corrected 2011 results (with corrections based on the detailed investigation shown in March of the problems reported back in February) and also the new 2012 results, which were taken with a kind of short-pulse beams similar to that used in OPERA-2. (A short pulse beam allows for a neutrino speed measurement to be made rather easily and quickly, at the expense of OPERA’s neutrino oscillation studies, which were the main purpose of building the OPERA experiment.)
Following Dracos’ talk, Bertolucci spoke next, and reported the results of the neighboring Borexino, LVD and ICARUS experiments on the May 2012 data, which along with OPERA are all bathed in the same CERN-to-Gran Sasso neutrino beam, and collected their data simultaneously. All of the results are preliminary so the numbers below will change in detail. But they are not going to change very much. Here they are: neutrinos arrive at a time that differs from expectation by:
- Borexino: δt = 2.7 ± 1.2 (stat) ± 3 (sys) ns
- ICARUS: δt = 5.1 ± 1.1 (stat) ± 5.5 (sys) ns
- LVD: δt = 2.9 ± 0.6 (stat) ± 3 (sys) ns
- OPERA: δt = 1.6 ± 1.1 (stat) [+ 6.1, -3.7] (sys) ns
(Here “ns” means nanoseconds, and ”stat” and “sys” mean statistical and systematic uncertainty.) The original OPERA result was an early arrival of about 60 nanoseconds, about six standard deviations away from expectations. You see that all the experiments are consistent with zero early/late arrival to about 1 standard deviation — almost too consistent, in fact, for four experiments.
So there is no longer any hint of any evidence whatsoever of a problem with the predictions of special relativity, and in particular with the existence of a universal speed limit.
A summing up is called for, but I want to write that carefully. So unless something else comes up, that’s all for today.