Wednesday, September 28, 2011

Don't Jump to Conclusion Faster Than c!

Needless to say, I've had a lot of questions coming my way regarding the recent neutrino results from OPERA. You'll notice that I've tried to refrain from making any kind of analysis and commentary on this thing. But it appears that my lack of response to it seems to be causing even more questions and prodding for me to say something.

Actually, I intend to. However, I need to know quite a bit more of what is going on beyond just what they had put down on their preprint. And being at a place where I have access to people who work at CERN (through the ATLAS collaboration), and people working on MINOS, provides me some advantage of talking to them and getting their feedback. But that takes time, because these people themselves are inundated with similar questions.

I'm saving more of my comments till later next week. That's when the MINOS people here will have a chance to make their presentation and comments on this result. However, just to wet your appetite, I will describe the common theme that has been running through many of the people I've spoken to.

A very important factor here is the pulse length. The proton beam that hits the target as about, what, microsecond pulse length. This beam collision with the target creates muons, etc. that will eventually decay and create the neutrino beam in that same direction. Now, it is assumed (with good reason), that the neutrino beam will ALSO have that same pulse length. So when the neutrinos are detected, one expect the same pulse length. It is from such observation that they deduce the speed of the neutrino, very much like measuring the group velocity.

The problem here is that, the proton beam itself is quite long. If one studies the beam dynamics, one can easily envision that the tail end of the proton beam might get affected by the kicker, and that can lead to the beam not having the exact pulse length as expected when it hits the target. This affect is a bit more difficult to find and detect, unlike, say, the electronics and timing, where one can change things to double check if one gets the same thing.

There's plenty of reasons to be skeptical of the result, as one should be, as of now. We just need to let the process work itself out. I'm pretty sure the folks at MINOS and T2K will be looking at this more closely. They hold the key to the independent verification/falsification of this observation, and they are the only ones that can do that. Jumping to conclusion right now and making speculative scenario of what would happen if this is true is highly and truly premature.

Zz.

4 comments:

Logan Wright said...

Thanks. I am worried about public perception of physics in general and, in particular, particle physics. Many of my non-scientist friends have mentioned that major news coverage has been pretty negative as of late; impatience over a Higgs or DM result and now impatience over this curiosity. On one hand, I understand the tendency to be cautious and assume an error but I think the best thing physicists can do is maintain a true skeptical, scientific view and withhold any judgement until we have more evidence. I understand your expertise gives you a little more in the way of default evidence on which to build mildly legitimate speculation and I've been eager to hear your thoughts. That said, I think the best thing is precisely what you have been doing; to suspend analysis until sufficient evidence is available.

ZapperZ said...

You should never forget to remind them that, unlike politics or economics (or any other social sciences), a negative result (or a non-result) can actually be a good thing! The Michaelson-Morley result is one such example. Not finding something in the range that one is looking for means that one can exclude parameters within that range, and allows us to narrow the physics.

So unlike many other areas, not finding something is actually an expansion of our knowledge in science! There are a lot of physicists would be THRILLED if the Higgs isn't found. This is because it means that the Standard Model has major fundamental issues to be resolved, and thus, there's a lot of new physics yet to be discovered. This will falsify those who think that the "End of Physics" is near.

Zz.

Pi-Guy said...

It's like back in the '90s before the Top Quark was found. I saw a documentary around that time about hunting for the Top. There were a number of interviews with scientists, one of which was Weinberg. His take, which contrasted with some of the others', was that a lot of physicists hoped the Top wouldn't be found, which would then place new, specific demands on theory, and thereby a better theory could be made. The historical success of the Standard Model has also been a liability, in some ways.

Josh said...

A question concerning the validity of using supernova 1987a as a gauge for speed of the neutrinos. I did a little bit of research and the detectors involved in the discovery of the neutrinos emitted from 1987a had a working range of 1983-(to pretty much present time). Now with using the speed received from the results at CERN-Gran Sasso the expected arrival of the neutrinos to earth should have been close to 4 yr +/- 1yr. This brings the arrival time beyond the range of any active neutrino detector that I am aware of, so how can they rule out the superluminal neutrinos from the 1987a event?