Tag Archives: CERN

Neutrinos and speed of light

Posted by on September 23, 2011 3 comments | 3,947 views

I just finished watching the 2 hour long webcast from CERN about the very surprising results that neutrinos have been measured with a velocity greater than the speed of light by a couple of thousandths of percent. If this turns out to be correct, i.e. can be confirmed by other neutrino experiments, it may have great implications for our current understanding of physics. It may not necessarily prove current physics wrong, it may just put a limit on the range of current physics. I.e. there may be new theories that will explain these results without having to chuck “old physics” in the bin in the same way as Einstein’s physics did not replace Newtonian physics as such, but expanded on it. That is after all what the LHC was built for.

So what are the results from OPERA? Well in a nutshell from the conclusion of the presentation:

Conclusion 1Basically what this says is that the neutrinos arrived at the detector some 730 km from the point they were created 60.7 nanoseconds before a photon would have arrived had it undertaken the same trip.

The big question is of course: are the measurements correct? The big points here are the synchronization of the clocks at both locations and the accurate measurement of the distance between them. The paper from arxiv.org linked below describes in detail how these are calibrated and how accurate they are. Another point, and this is probably where the error is made, is how they fit the plots of the arriving neutrinos. The 60 nanosecond shift produces the best fit, but I don’t think this looks very convincing (as discussed in the link to Résonaances below).

Other previous measurements of neutrinos from supernovae have not shown this result. This question was asked in the Q&A session after the presentation, and the answer given was that these are high-energy neutrinos at 17 GeV. Supernova-neutrinos are not, they’re in the 10 MeV range, so a factor of a thousand less. As you may know, nature does a lot more funky stuff at high energy than at low energy, another reason for building machines like the LHC. What needs to happen now is to have some of the other experiments try to reproduce this result at the same energies.

The article from NewScientist below also gives a possible explanation for this phenomenon using extra dimensions.

Regardless, time will show if this result is real or a fluke of some sort. If it turns out to be real, it requires explanation, and that’s where all the fun begins … for physicists at least!

Further reading:

Other comments:

Updated 24.09.2011

No new physics … yet

Posted by on August 30, 2011 2 comments | 1,588 views

LHCI have left the field of particle physics for computational physics (quantum mechanics in many-particle systems), but I still follow what happens at CERN and the LHC. Especially the blog Résonaances is a good source for updates.

Latest news is that the LHCb detector has not detected any anomaly in the Bs-Bsbar mixing. Bs-mesons are heavy mesons made up of a bottom-quark and a strange-quark. One matter and the other one anti-matter (the only possible way to combine two quarks due to colour-charge restrictions). These mesons however will oscillate between two states. Essentially the quarks swap who is the matter and who is the anti-matter particle through an exchange of virtual top-quarks (mostly) and W-bosons. Current physics predicts that this mixing violates conservation of charge/parity (CP), however so-called new physics—essentially what the LHC was built to find—predicts a larger violation. This has not been found. Which is disappointing. Why the need to find “new physics”? Well, because the Standard Model is incomplete. It doesn’t explain all the phenomena we observe—like dark matter for instance—so we need to figure out what’s missing from the theory.

This is also of course the case for the infamous Higgs. The last particle predicted by the Standard Model that not yet has been discovered. Not that it is far behind the rest. The top-quark wasn’t confirmed until 1995.

The problem with the Higgs is that the theoretical model (electroweak theory) of the Higgs has two unknown parameters. For this reason we don’t quite know where to find the Higgs (essentially how heavy it is). However we have a fairly good idea of how it will behave depending on how heavy it is, so we can look for signs of its presence along the mass axis in the data. The other challenge is that the Higgs resonance is in most cases so weak that it drowns in background “noise” from other more common processes. Or in other words. Many other particles do the same thing as the Higgs. Like the Z-boson. So how do you tell which did what? Well, that is the challenge.

The latest news from ATLAS and CMS is that they have excluded the Higgs from 145 to 466 GeV. The old exclusion was a lower bound of 115 GeV from back when the LEP accelerator was running at CERN and from Tevatron in the US. Tevatron also gave us an exclusion range in the 150-ish to just over 180 GeV range. The new limits now leaves us with the 115-145 GeV window. The Higgs is running out of places to hide … if it exists at all.

The relevant posts from Résonaances:

First Collisions in the LHC

Posted by on November 24, 2009 No comments | 2,670 views

 

CMS data at LHCYesterday a test run of the Large Hadron Collider at CERN produced the first collisions and collision data after 20 years of construction and preparations. They produced collisions in ATLAS, ALICE, CMS and LHCb. The beam was running at injection energy, so no acceleration. Next steps will be to crank up the power. This is looking promising so far, and I hope it all runs well. People were really excited here at the Institute of Physics in Oslo yesterday when they followed the unexpected test run online. Too bad I wasn’t there myself at the time, so I didn’t get to see the live feed.

Full CERN Press Release: press.web.cern.ch