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New Particle Discovered At CERN 144

Posted by Soulskill
from the lhc-stories-not-about-the-higgs dept.
New submitter ph4cr writes with news that a new particle has been discovered at CERN that confirms theoretical predictions. A pre-print of the academic paper is available at the arXiv (PDF). From the article: "Physicists from the University of Zurich have discovered a previously unknown particle composed of three quarks in the Large Hadron Collider (LHC) particle accelerator. A new baryon could thus be detected for the first time at the LHC. The baryon known as Xi_b^* confirms fundamental assumptions of physics regarding the binding of quarks. ... In the course of proton collisions in the LHC at CERN, physicists Claude Amsler, Vincenzo Chiochia and Ernest Aguiló from the University of Zurich's Physics Institute managed to detect a baryon with one light and two heavy quarks. The particle Xi_b^* comprises one 'up,' one 'strange' and one 'bottom' quark (usb), is electrically neutral and has a spin of 3/2 (1.5). Its mass is comparable to that of a lithium atom. The new discovery means that two of the three baryons predicted in the usb composition by theory have now been observed."
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New Particle Discovered At CERN

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  • by Anonymous Coward

    Are all particles named so oddly?

    Bring on the explanation for the lazy, science geeks.

    • by Entropius (188861)

      Wikipedia has a succinct explanation for the baryon naming rules.

      It's a holdover from before quarks were known, and all these things were thought to be fundamental.

    • Re: (Score:1, Insightful)

      by Anonymous Coward

      It's LaTeX, you moron. It's the Greek letter Xi with a "b" in the subscript and a "*" in the superscript. So just call it Xi-b-star or Xi-b-asterix. Simple.

      • by maxwell demon (590494) on Saturday April 28, 2012 @03:19PM (#39833157) Journal

        It's LaTeX, you moron. It's the Greek letter Xi with a "b" in the subscript and a "*" in the superscript. So just call it Xi-b-star or Xi-b-asterix. Simple.

        And how would you write Xi-b-obelix? ;-)

    • by zAPPzAPP (1207370) on Saturday April 28, 2012 @10:24AM (#39831625)

      USB quark (1.0)

      • by mindwhip (894744)

        NO!

        This is the second usb quark they found so its USB 2.0!

        They still haven't found the third one...

        • by mindwhip (894744)

          Argh! And of course I meant...

          NO!

          This is the second usb configuration baryon they found so its USB 2.0!

          They still haven't found the third one...

          I fell into a trap :(

          • by zAPPzAPP (1207370)

            After giving it extra thought, I am sure it's actually USB 1.5.

            (which, as they also found out, is 3/2)

    • by Danzigism (881294)
      baryon, also known as O_o
    • by physburn (1095481) on Saturday April 28, 2012 @01:13PM (#39832529) Homepage Journal
      It names after the Gell Mann's group of all particles that you can make with up,down and strange quarks, the Xi^0 particle is the name for the Baryon for the particle with two strange quarks and an a up quark. For heavier quarks, physicists write as a subsubscript the letter for an heavy quark replacing the strange quark.

      The Baryon multiplets are.

      Spin 1/2 (you can draw this as a hexagon)
      Xi^0 Xi^-
      Sigma^- Sigma^0 Sigma^+
      Lambda
      Neutron Proton

      Spin 3/2 (draw this as a triangle)
      Omega^-
      Xi^0 Xi^-
      Sigma^- Sigma^0 Sigma^+
      Delta^- Delta^0 Delta^+ Delta^++

      There are plenty of Baryons yet to be found, including most massively of all, the Omega Triple Bottom, which is (bbb) instead of (sss)

    • by kevingolding2001 (590321) on Saturday April 28, 2012 @03:01PM (#39833085)

      Physicists from the University of Zurich have discovered a previously unknown particle

      I'm going to go with "The particle formerly known as unknown", or just "The particle".

    • by RockDoctor (15477)

      Are all particles named so oddly?

      What's so difficult about "Xi bee star"? I mean, it even alternates most of it's consonants with vowels. As names go, it's not just a pussycat, but it's rolling in your lap, purring.

  • I'm only just now using devices ready for usb 3.0, and here comes another one.
  • I just wish they had named it something pronounceable. "Chi b to the asterix" just doesn't flow off the tongue too well.. :)

    • by SQL Error (16383)

      Kibitoaster.

    • chi b star (Score:5, Informative)

      by Roger W Moore (538166) on Saturday April 28, 2012 @10:03AM (#39831541) Journal
      It's pronounced "chi b star" and the discovery was by the CMS collaboration. The analysis was done by physicists from Zurich (apparently including one of my former postdocs) but they require data generated by the experiment so typically we credit the experiment. The discovery is of a new bound state of 3-quarks - not a new fundamental particle - so while interesting and definitely worthwhile it is not particularly exciting.
      • by zAPPzAPP (1207370) on Saturday April 28, 2012 @10:25AM (#39831635)

        So it was named after a Sailormoon character?

      • Re:chi b star (Score:4, Informative)

        by Snowtred (1334453) on Saturday April 28, 2012 @11:37AM (#39831945)

        Actually, this is the "Xi B Star" or "Cascade B Star". The "Chi b" particle has already been found, but is a completely different type of particle (meson, with quark and antiquark) than the "Xi b" (baryon, with 3 quarks)

        • Re:chi b star (Score:5, Informative)

          by FrootLoops (1817694) on Saturday April 28, 2012 @04:37PM (#39833483)

          This discussion made me wonder where the new particle falls in standard particle classifications. I've always been curious so I finally looked it up. My notes are below if anyone else is curious. I abbreviated the fundamental forces as (G)ravity, (E)lectromagnetic, (W)eak, (S)trong.

          (1) Elementary particles: indivisible (probably). Includes fundamental fermions and bosons.
                  (A) Fundamental fermions: obey Pauli exclusion principle and Fermi-Dirac statistics. Includes quarks and leptons.
                          (I) Quarks: six flavors; combine in groups of two or three; interacts with GEWS. The "S" allows atomic nuclei to exist.
                          (II) Leptons: six types, three charged, three not.
                                    (a) Charged leptons: mostly, the electron. Interacts with GEW. The "E" there makes chemistry work.
                                    (b) Uncharged leptons: neutrinos. Interacts with GW, so not much with ordinary matter.

                  (B) Fundamental bosons: obey Bose-Einstein statistics, disobey Pauli exclusion principle. Includes gauge bosons, Higgs boson, and gluons.
                          (I) Gauge bosons: force carrying particles. Photons carry E, W- and Z-bosons carry W, gluons carry S.
                          (II) Higgs boson: would explain the non-masslessness of some fundamental particles. Currently the only unobserved standard model particle.
                          (III) Graviton: would carry G. Theoretical status somewhat uncertain; not a standard model particle; currently unobserved.

          (2) Composite particles: composed of multiple elementary particles. Includes hadrons, atoms, molecules.
                  (A) Hadrons: two or three quarks held together by S. Includes baryons and mesons.
                          (I) Baryons: fermions made of three quarks. Most famous examples are protons and neutrons. Huge variety--~hundreds or more depending on how you count.
                          (II) Mesons: bosons made of two quarks. All unstable. Huge variety--~hundreds or more depending on how you count..

          Note that each particle has an anti-particle, where each composite particle's anti-particle is obtained by replacing the constituent elementary particles with corresponding anti-particles.

          The \Xi_b^{*0} particle (the summary left off the 0 for some reason...) is a baryon, so it falls under (2AI) in the above list. In light of the variety of the hadrons and their composite particle nature, this story isn't terribly exciting (at least to me).

          [Please correct any mistakes; I'm not a physicist.]

          • Re:chi b star (Score:4, Interesting)

            by Snowtred (1334453) on Saturday April 28, 2012 @05:12PM (#39833621)

            Your summary seems good. Although for your Hadrons, its better to understand that, a Baryon contains 3 quarks and an Antibaryon contains 3 anti-quarks. The meson, however, contains a quark and an antiquark. Two quarks or two anti-quarks are never stable. This is due to Color Confinement.

            A quark can contain a Red, Blue, or Green color. An antiquark can contain an Anti-red, Anti-blue, or Anti-green color. Any stable particle must be colorless, or white. You can make White with Red+Green+Blue (Baryons), Anti-Red+Anti-Green+Anti-Blue (Anti-Baryons), or Red+Anti-Red, Green+Anti-Green, or Blue+Anti-Blue (Mesons)

          • by Anonymous Coward

            This is a good summary: see:

            http://www.cpepweb.org/cpep_sm_large.html

            (2)(A)((I) Baryons: Proton is 3 quarks, (uud) Neutron is 3 Quarks: (udd), and this new Xikey one is (usb), where as a lambda is (uds) spin 1/2, and the omega is (usb) vs (dct) ( both would be 3/2 spin ).

            "A weird thing about hadrons is that only a very very very small part of the mass of a hadron is due to the quarks in it. For example, a proton (uud) has more mass than the sum of the masses of its quarks:

            Most of the mass we observe in a

        • Sorry - #$%@! autocorrect 'fixed' it and I did not notice, I've clearly written chi-squared too many times!
      • while interesting and definitely worthwhile it is not particularly exciting.

        maybe not. But the asterisk tells us the baryon itself is excited.

      • by blue_teeth (83171)
        If it has anything remotely to do with Chi-Square symbol (the X which I cannot reproduce here), then it is pronounced as Kai-Square.

        Just saying.
      • Oh no, not chibi star lol. As if it didn't already look enough like some 12 year old's username from an anime MMORPG or something, they had to made it be pronounced chibi? :-P (btw chibi = huge head, huge eyes, small body in anime).
        They should have just named it "Steve" or something.
      • It's not pronounced chi, it's pronounced xi. The chi particle is a meson not a baryon, the xi particles are baryons.
    • by Anonymous Coward

      The "Xi" greek letter is quite often refered to as "cascade" by particle physicists. I would say "cascade b zero star" when discussing this particle with colleagues.

    • by AngryDill (740460)
      It kind of flows when you pronounce each character...

      Zion Der Scorby Kara Tasterisk
    • by quenda (644621)

      I just wish they had named it something pronounceable. "Chi b to the asterix" just doesn't flow off the tongue too well.. :)

      They ran out of cool names, so they started using obscure smileys, it would appear.

  • by olsmeister (1488789) on Saturday April 28, 2012 @09:47AM (#39831479)
    I don't understand much about particle physics, but perhaps someone could give a quick explanation of how a particle made of three quarks has a mass equivalent to an entire atom of atomic number 3 and atomic weight almost 7? Is it because a bottom quark is one of its constituents?
    • I can't claim to understand much about particle physics, but I would guess that this particular arrangement of quarks has a bigger interaction with the Higgs field, thus making it more massive.

    • by Anonymous Coward on Saturday April 28, 2012 @09:55AM (#39831511)

      Protons and neutrons are composed of strictly up and down quarks, in (uud) and (udd) combinations for protons and neutrons respectively. Up quarks weigh about 2.5 MeV and down quarks weigh about 5.0 MeV. A strange quark weighs about 100 MeV, and a bottom Quark weighs (very) roughly 4.2 GeV. It's because of the bottom quark that Xi_b^* weighs so much.

      Source: http://pdglive.lbl.gov/Rsummary.brl?nodein=Q123
                              http://pdglive.lbl.gov/Rsummary.brl?nodein=Q005

      • by BlueParrot (965239) on Saturday April 28, 2012 @11:16AM (#39831865)

        It gets even more amusing when you consider that a proton has a mass of about 938MeV/c , whereas the three quarks it is made up doesn't even add up to 10MeV/c. The binding energy of protons and neutrons is immense compared to the particles they are composed of.

        • by LeDopore (898286)

          It's not so much the binding energy as the number of gluons in the proton that give it its mass. Binding energy would *decrease* the mass of the proton.

          PS I can't believe "gluons" isn't in the Firefox spelling dictionary.

        • by Old Wolf (56093)

          Perhaps a better explanation is to say that a proton consists of dozens of quarks and gluons of various flavour, colour, and anti-ness, however it has an excess of two more up quark than up antiquarks, and one more down quark than down antiquarks. The evidence for this is that when the LHC collides protons, the vast majority of observed interactions are gluon-gluon, or low energy quarks (as evinced by the energy of the products).

          For more info see http://profmattstrassler.com/articles-and-posts/largehadron [profmattstrassler.com]

      • by Nivag064 (904744)
        Yes! Protons and Neutrons are straight up & down particles - not like the ones that are strange or have charm... :-)
    • by Zocalo (252965)
      Firstly, remember that mass != weight. Mass is all to do with energy (as in e=mc^2), and bottom quarks have lots of energy - just over 4GeV compared to the ~2.5MeV (up) and ~5MeV (down) of the quarks that protons and neutrons consist of.
      • Re: (Score:3, Interesting)

        by Immerman (2627577)
        It's worth noting that the composite particle's masses are generally due primarily to the massless gluons who's immense energy contributes to the bound particle
        Proton (uud): ~10MeV/c^2 in quarks , 938MeV total
        Neutron (udd): ~12.5MeV in quarks, 940MeV total
        Xi_b^* (usb): ~4293MeV in quarks, ~6517MeV total (7amu * 931 MeV/amu)
        So not only is Xi_b^* composed of much higher mass quarks, but it would appear to have roughly twice the binding energy as well.

        But why mention mass != weight? In a uniform gravit
  • Funny. (Score:5, Insightful)

    by Milharis (2523940) on Saturday April 28, 2012 @10:04AM (#39831545)

    I find it funny that TFS talks about a Xi_b^* baryon with usb quarks, and goes on about its spin, as if it was common knowlegde, but has to precise that 3/2 is 1.5.

  • by Anonymous Coward on Saturday April 28, 2012 @10:12AM (#39831581)

    ... and has a spin of 3/2 (1.5). ...

    I don't know about the rest of the summary, but I can confirm that 3/2 is in fact 1.5.

  • Tiny little particle; huge godlike pricetag.

    • by jo_ham (604554) <joham999&gmail,com> on Saturday April 28, 2012 @11:05AM (#39831817)

      Indeed, without having that massive boondoggle at CERN we could have funded at least 1 more month of the Iraq war!

    • Re: (Score:3, Interesting)

      by Snowtred (1334453)

      I know this is slightly in jest, but this paper is not the sum-total of all of the work at the LHC.

      There are 6 projects, each with hundreds of scientists, all of whom are juggling many papers at once. This Xi stuff is completely independent from Higgs searches, and it is one of many particles already discovered or confirmed at the LHC. So this isn't a Higgs-worthy discovery, although I think it is pumped-up a bit because CERN has really good press, and it looks good that the LHC is finding new physics.

      Oth

      • by Shavano (2541114)

        I know this is slightly in jest, but this paper is not the sum-total of all of the work at the LHC.

        There are 6 projects, each with hundreds of scientists, all of whom are juggling many papers at once. This Xi stuff is completely independent from Higgs searches, and it is one of many particles already discovered or confirmed at the LHC. So this isn't a Higgs-worthy discovery, although I think it is pumped-up a bit because CERN has really good press, and it looks good that the LHC is finding new physics.

        Otherwise, this would just be a normal story. New Baryons or Mesons (like this one) are found a few times a year.

        I know this is slightly in jest, but this paper is not the sum-total of all of the work at the LHC.

        There are 6 projects, each with hundreds of scientists, all of whom are juggling many papers at once. This Xi stuff is completely independent from Higgs searches, and it is one of many particles already discovered or confirmed at the LHC. So this isn't a Higgs-worthy discovery, although I think it is pumped-up a bit because CERN has really good press, and it looks good that the LHC is finding new physics.

        Otherwise, this would just be a normal story. New Baryons or Mesons (like this one) are found a few times a year.

        It's interesting that it's yet another confirmation of the standard model. Calling it "new physics" is probably a little bit of an overstatement, since everybody expected that this particle was one of the ones that they would be able to prove out. It's a new and confirming result. I would go so far as to say something is "new physics" if it was weird enough to call the standard model into doubt, or if a neutrino really did travel faster than the speed of light, or if it looked like confirmation of a new

        • by Snowtred (1334453)

          The "hundreds of scientists" bit wasn't an argument for the LHC producing jobs, but just that there are hundreds of scientists each working on several papers that are all producing interesting results. So the fact that we see "New particle at LHC" articles everywhere after several months of running is misleading, as several LHC-related papers are put on the arxiv each week.

        • by hkmwbz (531650)
          It's not just about curiosity. Even thought a discovery might not have practical uses today, it might in the future.
          • by Shavano (2541114)

            It's not just about curiosity. Even thought a discovery might not have practical uses today, it might in the future.

            If there's no specific intent to use the information, it's basic research and we really do that to satisfy our curiosity. In particle physics, we are probably far past the point where there's any reasonable expectation that the results of the experiments will have any practical application.

  • by krzysz00 (1842280) <krzysdrewniak@g[ ]l.com ['mai' in gap]> on Saturday April 28, 2012 @11:01AM (#39831803)
    Xi_b^* is actually the LaTeX code needed to generate the name of the particle. The particle's name is actually this (png image) [equationater.com]
  • \Xi_b^*0 is part LaTeX for greek capital xi which gives the particle a Unicode identity of subscript b superscript * 0 - \Xi_b^{*0} ;)
  • Xi_b^* ? (Score:3, Funny)

    by DJCouchyCouch (622482) on Saturday April 28, 2012 @11:40AM (#39831979)
    Someone's been looking at my coworker's variable names.
  • Baryon Discoveries (Score:5, Insightful)

    by Snowtred (1334453) on Saturday April 28, 2012 @11:44AM (#39832025)

    I just want to provide a little context to this announcement. As shown in the article, this is a Baryon, made up of 3 quarks. With 6 possible types of quarks, and 3 spots, this makes for many possible combinations of Baryons, a lot that have been found. Here is a current list of baryons:

    PDG Baryon List [lbl.gov]

    The proton and neutron are the p and n in the top left. The new Cascade (Xi_b) will be in the bottom right, in the "Bottom quark" section.

    So this is neat and all, but hyped up a bit because its the LHC. A couple of these new Baryon (and also Mesons) are confirmed every year.

    • The thing I don't get is, how can a single particle comprised of just 3 quarks be comparable in mass to an entire atom (lithium atom) as stated in the summary? I realize lithium is low on the scale with only 3 protons, but still, even protons, being fermions, are comprised of 3 quarks each, as I understand it..seems counter intuitive. Does it depend on the combination of the types of quarks?
      • by Snowtred (1334453)

        Most of the energy is the "binding energy" or in this case, the energy of the gluons mediating the strong force that holds the quarks together. The actual sum of the 3 quarks is only a small part of the total mass. But with E=mc^2, Mass and Energy are equivalent, and the large amount of energy binding the 3 quarks together becomes the mass.

      • Different quarks have different masses. The ones forming protons and neutrons (u, d) happen to be the most lightweight of all.
        • by kyrsjo (2420192)

          And also different combinations of quarks has different energy, which begets different total mass - the whole is greater than the sum of its parts.

          Take for example the proton or the neutron, where the mass of the elementary u/d quarks are only a couple of MeV each, while the whole composite particle clock in at almost 1000 GeV. This is due to energy trapped in the binding- and kinetic energy inside the protons and neutrons.

          Additionally, you can also "gain" mass without adding or changing particles, by exiti

        • by Old Wolf (56093)

          Different quarks have different masses. The ones forming protons and neutrons (u, d) happen to be the most lightweight of all.

          It's not really a coincidence; stable matter is formed of the two lightest types of quark, because the heavier types are unstable by definition (they are not the lightest type, so they tend to decay into the lightest type).

      • by Old Wolf (56093)

        The thing I don't get is, how can a single particle comprised of just 3 quarks be comparable in mass to an entire atom (lithium atom) as stated in the summary? I realize lithium is low on the scale with only 3 protons

        The quark masses are , in MeV and fairly approximately: up=3, down=5, strange=101, charm=1270, bottom=4190, top=172000

        The atomic weight of lithium (6-7 nucleons) is 6.941, so this is a mass of about 6500 MeV . As you can see, it is the single bottom quark that provides the bulk of the mass in a bottom baryon. (Of course, the mass in the form of kinetic energy of quarks and gluons, and rest mass of gluons and 'sea' quarks and gluons, as mentioned by other posters, is also a factor)

        [all data from Wikipedia

  • Whenever new particles are discovered I always think of this comment regarding the Muon [wikipedia.org]
  • bah humbug g'me an event horizon to bewonderlment at
  • by JustNiz (692889)

    Meh. They could make it spin twice as fast just by using usb2.

  • by spike1 (675478) on Saturday April 28, 2012 @10:13PM (#39834977)

    The gayon...

    After all it is composed of up strange bottom quarks... :)

  • It's turtles all the way down.

  • I want one!

  • ..." two of the three baryons predicted in the usb composition by theory have now been discovered."

    Does this mean that CERN is usb compatible?

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