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Fermilab Not Dead Yet, Discovers Rare Single Top Quark 194

Posted by ScuttleMonkey
from the emphasis-on-the-operating dept.
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."
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Fermilab Not Dead Yet, Discovers Rare Single Top Quark

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  • And (Score:5, Funny)

    by Mozk (844858) on Monday March 09, 2009 @06:12PM (#27128063)

    This quark was not charmed by being photographed.

    • Re:And (Score:5, Funny)

      by Amazing Quantum Man (458715) on Monday March 09, 2009 @06:21PM (#27128181) Homepage

      That sounds rather strange.

      • Re:And (Score:5, Funny)

        by Anonymous Coward on Monday March 09, 2009 @06:22PM (#27128197)
        Should I mod this "up" or "down" ?
    • Re:And (Score:4, Funny)

      by CaptainPatent (1087643) on Monday March 09, 2009 @06:21PM (#27128185) Journal

      This quark was not charmed by being photographed.

      Strange.

      • Redundant!?

        It was a quantum finish!
        • Re: (Score:3, Insightful)

          by lorenlal (164133)

          Agreed. Moderators were distracted by the plethora of particular humor above, and didn't notice that this post that was marked "redundant" was posted WAY before most of the jokes above. At 7:43 this was a perfectly legit comment.

          Please mods, correct this. This only encourages usage of the FRPoR (first reasonable post or reply) for all future moderation or karma gains. This was quite funny, and I am giving CaptainPatent a +1 in my mind.

    • Re: (Score:2, Funny)

      by Kjella (173770)

      No, but the girl [xkcd.com] was. Ok, a badly drawn stick girl in a webcomic was anyway ;)

    • Re: (Score:2, Funny)

      by amchugh (116330)

      Single top quarks can't be charmed without becoming topless, and then they don't like to be photographed until you ply them with enough drinks that they collapse.

    • by mcgrew (92797)

      Dabo!!

  • if school children will ever get taught about quarks. I mean, most 10 year olds can tell you about protons, electrons and neutrons.

    • by Zerth (26112)

      It was in my highschool text book ten years ago. The teacher never got that far, but it was in there.

      They're probably still using the same book. I was rather lucky that they had just bought new books, considering it'd been at least 15 years since the last update before that. My book the grade before still had the "raisins in pudding" model of atoms.

    • if school children will ever get taught about quarks. I mean, most 10 year olds can tell you about protons, electrons and neutrons.

      Perhaps when they find some use for quarks, they'll start teaching schoolchildren about them.

      • Re: (Score:3, Insightful)

        by Jamamala (983884)
        How about explaining why protons have a +1 charge and neutrons have no charge? I'd say that's pretty useful. Ditto with explaining the charge of the anti-nucleons.
        • Re: (Score:3, Interesting)

          How about explaining why protons have a +1 charge and neutrons have no charge? I'd say that's pretty useful. Ditto with explaining the charge of the anti-nucleons.

          Actually, they don't explain "why" they have +1 charge. Merely elaborate on the idea that they do so.

          Note also that the reason that protons have +1 charge isn't especially useful, in and of itself. Interesting, perhaps, but not useful.

          • Re: (Score:3, Insightful)

            by dtremenak (893336)

            Interesting, perhaps, but not useful.

            All the more reason to teach it. We should be trying to get students interested in science.

            • We should be trying to get students interested in science.

              You'll get more students interested in science by demonstrating that it's useful and at least slightly fun. You won't get students interested in science by telling them that quarks make the math come out right.

      • by bunratty (545641)
        I'm made of quarks, you insensitive clod!
      • by lorenlal (164133)

        At 10, I could have told you about quarks... But I would've told you that the best use of them involved reciting the Rules of Acquisition.

      • If you think quarks are useless, eliminate them from your life and see what happens.

    • Admittedly, I was homeschooled, but I was taught about quarks.
    • I got taught about quarks at secondary school years ago in the UK. As a particle physicist who was actually involved in this analysis I now go to schools and give talks about particle physics and they have usually heard of quarks (here in Canada) even if they are not quite sure what they are.
  • Better Post (Score:2, Informative)

    by Anonymous Coward

    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]

  • Bare/Single quark? (Score:4, Interesting)

    by cblack (4342) on Monday March 09, 2009 @06:27PM (#27128251) Homepage

    Just to be clear, this isn't a single/bare quark w/o a partner is it? As I thought isolating quarks outside of a hadron (w/ 1 or 2 other quarks) was not possible due to the nature of the strong force. Is what they are really saying is that they got an event to force just one top quark to decay once released from a hadron rather than 2 or more at once?

    • by BitterOak (537666)

      Yes, quarks produced via the strong (or electromagnetic) interaction are always produced in quark/anti-quark pairs. So a strongly produced top quark would always be produced with an anti-top quark. Those two quarks would not generally end up in the same hadron, but they would both be produced at the same time.

      The weak interaction can change quark flavors, so a top quark could be produced from some other flavor of quark, with no anti-top quark being produced in the event. All the quarks will end up in had

    • by parrillada (264680) on Monday March 09, 2009 @06:38PM (#27128357)

      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.

      • ...experimenters have more than doubled the amount of data analyzed and sharpened selection and analysis techniques, making the discovery possible. For each experiment, the probability that background events have faked the signal is now only one in nearly four million , allowing both collaborations to claim a bona fide discovery...

        Emphases mine... I am not convinced this isn't a faked signal. With that possibility having a chance of one in four million, how many millions of collisions have they done in the

        • by Phroon (820247) on Monday March 09, 2009 @09:46PM (#27130035) Homepage

          Emphases mine... I am not convinced this isn't a faked signal. With that possibility having a chance of one in four million, how many millions of collisions have they done in the past 15 years? Far more than 4 million, I would suspect.

          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.

          ...and another thing. Look at that diagram showing a muon went here and a neutrino went there - how in the world did they detect that neutrino, I ask? I bet it zipped right through their detector without so much a pausing to say hello.

          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.

      • by Roger W Moore (538166) on Monday March 09, 2009 @09:29PM (#27129871) Journal

        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.

      • by Phroon (820247) on Monday March 09, 2009 @09:51PM (#27130069) Homepage

        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.

        Single-top is, however, one of the backgrounds in the search for the Higgs boson. For Fermilab to discover the Higgs, they have to discover single-top first.

    • no it is not a 'free' quark. it can be produced as tsbar, tdbar or most likley tbbar as opposed to the more common ttbar pair.

  • I remember from the Usenet Physics FAQ [ucr.edu] that quarks are normally bound together too tightly to be observed (although that article is almost fifteen years old). Is this an exception or is something else going on? Have other single quarks been observed too?

    • by FooAtWFU (699187)
      Most of the time when a lab "observes" an interesting particle they don't actually detect it, they just detect all the crazy debris that it produces when it explodes^W decays.
  • The fine article says that this results limits the number of possible quarks. Can someone give an explanation (or even the outline of one) at a level that someone with a B.S. in physics can understand?

    • by Phroon (820247) on Monday March 09, 2009 @09:56PM (#27130097) Homepage

      The fine article says that this results limits the number of possible quarks. Can someone give an explanation (or even the outline of one) at a level that someone with a B.S. in physics can understand?

      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.

  • Are the top quarks rarer than the sub bottom quarks?
    • Re: (Score:3, Funny)

      Are the top quarks rarer than the sub bottom quarks?

      Yes, but they wear one of eight different colors of gluon in their left pants pocket so you can identify them easily.

  • The production of single top quarks, which involves the weak nuclear force and is harder to identify experimentally, has now been observed

    Pictures, or it didn't happen.

  • it is just not produced as a ttbar pair, rather it is a tdbar, tsbar or more likley tbbar. Just in case the 'single' confuses anyone.

  • by zappepcs (820751) on Monday March 09, 2009 @06:51PM (#27128463) Journal

    Fermilab seemed to be counted out, no longer useful, with the advent of the LHC? How many recent science ventures turned out to be more useful than originally thought, and initially thought less useful than a replacement?

    Space station? Hubble telescope? Mars rovers? ... you get the point. Why would anyone count Fermilab out? I just find that odd. Sure, it doesn't have the professed capabilities of the LHC, but then neither does the LHC right now. I seem to remember something about not fixing it if it ain't broke being relatively true.

    I expect more from Fermilab too.

    This is so much like American Idol or something ... gah!

    • Sure, it doesn't have the professed capabilities of the LHC, but then neither does the LHC right now.

      Exploding and releasing a lot of gas? [slashdot.org] Fermilab should go for Del Taco, they'd get right back in the game.

    • Not really suprising. I disagree in some sense, but it's not suprising. We've discovered close to (but as the article demonstrates not quite) everything we can discover at the energy levels the Tevatron can generate - Needs bigger particle gun. And if the new one at CERN doesn't help, the next new one will have to be bigger than earth :/
  • by DrBuzzo (913503) on Monday March 09, 2009 @07:25PM (#27128819) Homepage
    Ferbilab dead? Oh that must be because of the fact that the LHC is now the biggest and most powerful particle accelerator in the world, or will be once it starts again. Fermilab will only have the second most powerful one, which clearly is useless, right?

    Right... So by this logic every piece of scientific equipment in the world, no matter how capable or useful is not even worth keeping up once it is no longer the number 1 on earth. So lets just abandon all the telescope observatories in the world except for the largest. Then, when someone builds a bigger once, the previous largest will be second largest and therefore useless.

    Lets also scrap all the super computers in the world except for the most powerful one. Then when someone build a more powerful one, we'll scrap that one.

    The point being: it is still as useful as it ever was. There are energy levels that the LHC can achieve, but there are more than enough researchers who would just about kill to get time on any of the top 50 particle accelerators in the world.
  • I'm dumb, I think. (Score:3, Interesting)

    by bucky0 (229117) on Monday March 09, 2009 @08:25PM (#27129343)

    I thought unbound (single) quarks were didn't exist?

    • by jd (1658) <imipak@nOSPam.yahoo.com> on Monday March 09, 2009 @08:49PM (#27129561) Homepage Journal

      They do, but in the Middle East, they are not permitted to be seen in public without wearing a full atom.

    • First this is production of single top quarks, not production of a single quark. The production mechanisms we looked for always produce a top and a b quark together i.e. single as in one top quark as opposed to two top quarks.

      The top quark is unusual in that it only ever exists as an unbound quark. The reason is that it has such a large mass that it decays to a b quark so rapidly that it does not live long enough to become bound.
    • Re: (Score:3, Informative)

      by Phroon (820247)
      There's a few things going on here that are related in different ways.

      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

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