Comments on: Fermilab collider experiments discover rare single top quark

By: Kurt Riesselmann

Kurt Riesselmann — Sun, 01 Nov 2009 12:54:02 +0000

One aspect of science is that you don’t trust a theory blindly. If scientists did, people would never have questioned Newton’s explanation of gravity. So you need experiments to test all predictions of a theory, and you just don’t know when one of these tests will show a surprising result instead of confirming the expected. The top quark is very different from the other quarks. It is much, much heavier; it doesn’t live long enough to form composite particles; and theorists have developed models that suggest that the top quark could play a major role in understanding the origin of mass. To find out whether that is true, physicists need to measure and understand the various types of interactions that the top quark exhibits. This particular measurement was particularly hard — it took 14 years longer to observe the electroweak interaction of the top quark than to find its strong interaction — and is an important test of the Standard Model.

By: Samuel

Samuel — Sat, 31 Oct 2009 23:27:41 +0000

There is of course the possibility that this isn’t important or even interesting at all ! The way I understand it, this was just a confirmation of something they expected all along. Though I suppose it is comforting that the standard model is once again confirmed, I do not find this particularly exciting.

By: symmetry breaking » Blog Archive » Single top quark in the palm of your hand

Tue, 24 Mar 2009 15:25:12 +0000

[...] recently announced the first observation of the single top quark, a top quark produced without an anti-top quark. Fermilab physicists discovered the top quark in [...]

By: symmetry breaking » Blog Archive » What will it be? Fermilab announces new Higgs results Friday

Thu, 12 Mar 2009 20:32:21 +0000

[...] Just look at the discovery that the CDF and DZero collaborations announced less than a week ago: single top quark production. An amazing feat in its own right, the discovery also showed that the Fermilab Higgs hunters may [...]

By: Jim Lewandowski

Jim Lewandowski — Wed, 11 Mar 2009 23:53:09 +0000

Thanks for the explanation.

Jim

By: Kurt Riesselmann

Kurt Riesselmann — Wed, 11 Mar 2009 21:31:17 +0000

Jim and Howard: Neutrinos do not leave tracks in particle detectors. They are neutral particles, always travel in a straight line, and they very rarely interact with matter at all. (On the rare occasion that a neutrino hits an atom, then the charged particles emerging from that collision leave tracks. That’s how neutrino detectors work.) In the graphic above, the bent particle track that leads to the neutrino label is a coincidence. It is a different, charged particle with very little energy. (For comparison: the muon, a charged particle identified in the graphic, has high energy: it travels in almost a straight line, and the green block indicates its energy.) Neutrinos are idenfied by missing energy and momentum. The yellow block indicates that there is a lot of missing energy in this particular direction. How does the DZero collaboration know there is missing energy: it’s like seeing billard balls collide, and one ball is invisible. But knowing exactly the tracks and velocities of all other balls, you can identify the track and energy of the invisible ball.

By: symmetry breaking » Blog Archive » W boson squeezes Higgs particle

symmetry breaking » Blog Archive » W boson squeezes Higgs particle — Wed, 11 Mar 2009 18:09:56 +0000

[...] this month. Less than a week ago, the DZero collaboration submitted a paper on the discovery of single top quark production at the Tevatron collider. In the last year, the collaboration has published 46 scientific papers [...]

By: Blake Stacey

Blake Stacey — Wed, 11 Mar 2009 17:50:06 +0000

Would the actual neutrino track be shown on such a diagram at all? I mean, D0 isn't directly sensitive to neutrinos, is it? I would guess that (a) the muon had sufficiently high momentum that it didn't curve noticeably; (b) the yellow bar is the "missing transverse energy" carried off by the neutrino; (c) the curving track which ends at the yellow bar is actually a bit of random debris, not a neutrino (notice that it seems to have deposited a bit of energy of its own); (d) the "straight track directly opposite the muon" is actually part of a faint red triangle highlighting the tracks comprising one of the b jets (compare the image here, for example).

By: Howard Moon

Howard Moon — Wed, 11 Mar 2009 15:32:06 +0000

Jim, I think you’re right that the yellow segment is mislabeled. In other end-views of DZero I’ve seen related to top quark detection, it’s been labeled “Missing transverse energy”. If I’m not mistaken, the neutrino would move directly opposite to the muon, and is represented by the (faint) straight track directly opposite the muon.

By: Jim Lewandowski

Jim Lewandowski — Tue, 10 Mar 2009 17:46:36 +0000

Is your decay mislabeled? The neutrino shows an arc and the muon does not, neutrino is neutral and shouldn’t bend in the detectors field.

Jim