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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 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?
  • by Snowtred (1334453) on Saturday April 28, 2012 @11:40AM (#39831977)

    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.

  • by Immerman (2627577) on Saturday April 28, 2012 @11:47AM (#39832043)
    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 gravitational field mass and weight are directly proportional to each other and can be used interchangeably using the gravitational acceleration as the conversion factor. The distinction is only relevant if you're either
    1) operating within a non-constant gravitational field (i.e. in space) or comparing weights of different planets
    or
    2) You've discovered the first matter ever detected with different gravitational mass and inertial mass
    Since (1) doesn't apply, and (2) almost certainly doesn't the distinction seems irrelevant
  • 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)

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