Fermilab Not Dead Yet, Discovers Rare Single Top Quark 194
Several sources are reporting that in spite of LHC hype, Fermilab's Tevatron has produced another feat for scientific discovery. Currently the world's most powerful operating particle accelerator, the Tevatron has allowed researchers to observe a rare single Top Quark. "Previously, top quarks had only been observed when produced by the strong nuclear force. That interaction leads to the production of pairs of top quarks. The production of single top quarks, which involves the weak nuclear force and is harder to identify experimentally, has now been observed, almost 14 years to the day of the top quark discovery in 1995."
Better Post (Score:2, Informative)
You might find Tomasso's piece better - he works with the CDF group.
http://dorigo.wordpress.com/2009/03/05/who-discovered-single-top-production/ [wordpress.com]
Re:Bare/Single quark? (Score:5, Informative)
They are saying that the top quark is being produced one at a time, rather than in pairs (IAAP). It's actually subtle -- what had been observed before were 2 top quarks emerging from a gluon. Now they have observed one top quark (and another quark) emerging from a W-boson. Basically. This is not a major discovery, but it is another important showing off of the 'standard model' working very well at the energies we have so far probed.
Oh, and about isolating quarks. You cannot isolate a quark outside a hadron, but you can 'detect' the quark by observing the hadrons and leptons that it decays into, since they leave a distinct signature. The top quark is special because it decays before it even forms a hadron with other quarks.
Re:Bare/Single quark? (Score:1, Informative)
One of the papers is available [arxiv.org] on the arXiv, and it confirms that they were looking for top/anti-bottom pairs instead of the top/anti-top pairs produced by strong processes.
Re:And (Score:5, Informative)
Re:And (Score:3, Informative)
And as final tongue-in-cheek example, have you used the Internet lately? Invented at CERN.
WWW, not Internet. Some of us were perfectly happy with our Gopher and FTP before the new-fangled web stuff came along.
Re:And (Score:5, Informative)
And as final tongue-in-cheek example, have you used the Internet lately? Invented at CERN.
I'm guessing by "tongue-in-cheek" you mean "totally wrong".
The Internet was not invented at CERN -- it was invented by DARPA back in 1969 -- the World Wide Web (more specifically, HTTP) was invented at CERN.
Re:Bare/Single quark? (Score:4, Informative)
Now they have observed one top quark (and another quark) emerging from a W-boson.
Actually that is only one of the single-top processes that we looked for. You can also have a W-boson exchange which changes the flavour of two quarks, one of them into a top. With enough statistics you can distinguish the two different mechanisms and measure their ratio which is a good way to detect new physics.
You cannot isolate a quark outside a hadron... The top quark is special because it decays before it even forms a hadron with other quarks.
So, in fact, you can actually study isolated top quarks which are outside a hadron because the top quark never exists in a bound state. Indeed this is one of the interesting things about the top quark in that you can study the properties of an unbound quark.
Re:it's a faked signal (Score:5, Informative)
You aren't quite grasping what he means by one in four million. This wasn't a single event we are talking about here.
The way the statistics work is that you would have to run the entire Fermilab experiment four million times to get what they see from a fake signal. It's a cumulative probability over all the events ever recorded at Fermilab.
They didn't detect it directly. The key to 'detecting' the neutrino is to count up everything else in the remnants collision and notice that it recoils off of something that you didn't detect. It acts as though what you can see in your detector is violating the conservation of energy. But in reality there's an undetectable neutrino zipping through the detector. So you calculate how much energy and in which direction such a neutrino would travel in order to conserve energy, and that's where they get that little diagram.
Re:Explanation wanted (Score:5, Informative)
One of the things single-top is sensitive to is the coupling strength of the top and bottom quarks via the weak force. The value of this coupling is tightly constrained if one assumes that there are only six quarks (ie. there are three generations of matter). The fact that they measured it and it's within the six quark ballpark means that it is very likely that there isn't another pair of quarks waiting to be discovered.
The basic idea is that if the top and bottom coupling strength is measured to be less than the value we expect for six quarks then that means that some of that coupling strength actually goes to a different, seventh or eighth, quark. But I'm grossly simplifying things here for the general slashdot crowd.
Re:I'm dumb, I think. (Score:3, Informative)
1) The single-top isn't the only quark being produced, it's actually produced with a bottom quark at the same time. Usual top quark production is in pairs, one top quark one anti-top quark, but single-top is different; a top quark is produced with a anti-bottom quark.
2) The top quark decays before it can hadronize. That is, it decays before it can pick up a partner quark. This is completely allowed in the Standard Model, but I'm a bit sketchy on the details. I think it behaves as though it was attached with the other quark it was produced with.