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CERN & new particles

  1. May 7, 2007 #1

    jal

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    Would CERN produce enough energy to be able to produce a new particle made up of 6 quarks?
    Some might call it a heavy proton or a heavy neutron. When it broke up would it make two protons or two neutrons or one of each? Or something else?
    jal
     
  2. jcsd
  3. May 7, 2007 #2
    Why do you think such a particle should exist ? There are no reason a for such an "hexaquark" to be that heavy, so it would probably not require energies at the level of LHC. There were actual search for "dibaryons" in the past, leading to the belief that such particle do not exist, or at least not where we searched for them.

    It will become more and more difficult to search for such widely exotic QCD bound states. One could say that, in principles, QCD allows for such states and that, therefore, since Nature seem to realize what is allowed, they should exist. But unfortunately, the failure to confirm the recent "pentaquark" creates yet another "precendent". As of today, we will concentrate (in my opinion) on glueballs as well as low lying "hybrids" (that is to say, qqg, or a meson with an additional gluon, or again, the pair quark/antiquark with the glue tube excited in between). If no gluball, and no hybrid is to be found, people might then try to concentrate on why they do not occur.

    Frankly, the experimental situation is even opposite : we already have too many predicted bound states in the spectrum. There are widely known "missing resonances". The real mechanism for confinement being still unknown, it is easy to speculate that such exotics cannot exist either...
     
  4. May 7, 2007 #3
  5. May 8, 2007 #4

    Haelfix

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    There was a bit of excitement in my department some years ago about such creatures, somewhere around the pentaquark craze. At the time there was some developments in lattice QCD as well as a few analytic nonperturabitive and semiempirical bag models that allowed them to exist.

    Unfortunately further experimental searches and theoretical scrutiny pushed that likelihood further and further away.

    State of the art in the field now posits that in general if such a bound state could exist they would have such an enormous phase space as to be undetectable even indirectly, and many of the likely ways such a thing could come to exist have now been discredited.

    Personally, I am skeptical of most theoretical work in this strong coupling regime, and I tend to only rely on what lattice QCD tells us. I strongly suspect we won't ever do much better than simply ramping up the silicon density, though of course many physicists will disagree with me on this point.
     
  6. May 8, 2007 #5
    Hexaquarks may indeed be possible, and there are already some candidates. The new pseudoscalar X(1835) resonance may in fact be a low-mass hexaquark object, which in fact decays very strongly to a proton-antiproton pair. A charged version of the same basic isospin-1 quark content would probably decay into a proton-antineutron (positively charged) or neutron-antiproton pair (negatively charged). The energies necessary are already at our disposal at Fermilab and other similar proton synchrotrons.

    However, it would certainly not be called a heavy proton or neutron, because it will behave as a meson. The lowest lying hexaquark should be the pseudoscalar one (u d ubar dbar x ((u ubar +/- d dbar)/sqrt2)) if the Bag Model is even marginally accurate in nature. I would think it would "fall apart" quickly into a scalar (possibly sigma) meson and either a pion or eta meson.

    Now, an actual dibaryon resonance would be much heavier than a hexaquark according to the Bag Model, on the order of, say, 2500 MeV. This is much heavier than the mass of the two protons or two neutrons in combination, so the chances are that this dibaryon state will never exist in the necessary wavefunction at any energy.
     
    Last edited: May 8, 2007
  7. May 8, 2007 #6

    jal

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    I'll do the reccomended reading and come back.
    A quick scan of the articles seems to indicate that CERN's data analysist will be rejecting H-dibaryon events as being below their threshhold and part of "background noise". Is that correct?
    jal
     
  8. May 8, 2007 #7

    jal

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    Read your links .....Further searches gave me A power house!!!!
    http://cosmo.nyu.edu/glennys_farrar.html
    Farrar and grad student G. Zaharijas have shown that the baryon asymmetry of the universe may be only an asymmetry in "packaging", with the baryon number in nucleons balanced by anti-baryonic dark matter. Observational constraints on such DM have been obtained and are found to be consistent with the expected DM properties. In one such scenario the DM consists of H and anti-H dibaryons, impelling a renewed study of a long-lived H dibaryon.
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    http://arxiv.org/PS_cache/hep-ph/pdf/0303/0303047v1.pdf
    Transitions of two baryons to the H dibaryon in nuclei
    Glennys R. Farrar and Gabrijela Zaharijas
    05 march 2003
    I. INTRODUCTION
    The H dibaryon corresponds to the most symmetric color-spin representation of six quarks (uuddss). It is a flavor singlet state with charge 0, strangeness -2 and spin-isospin-parity I(JP ) = 0(0+). The existence of the H was predicted by Jaffe in 1977 [1] in the framework of the quark-bag model. Its mass was originally estimated to be around 2150 MeV, making it stable toward strong decay to two _ particles. Since then, there have been many theoretical efforts to determine its mass and production cross section and, on the experimental side, many inconclusive or unsuccessful attempts to produce and detect it.
    There are a number or possible reactions by which two nucleons can convert to an H in a nucleus. The initial state is most likely to be pn or nn in a relative s-wave, because in other cases the Coulomb barrier or relative orbital angular momentum suppresses the overlap of the nucleons at short distances which is necessary to produce the H.
    Note that the H does not bind to nuclei[15]; it simply recoils with some momentum imparted in its production.
    There are five experiments which have reported positive results in the search for single _ decays from double _ hypernuclei.
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    http://arxiv.org/PS_cache/hep-ph/pdf/0508/0508150v1.pdf
    Flavor-singlet hybrid baryons may already have been discovered
    Olaf Kittel
    Glennys R. Farrar
    12 Aug 2005
    The hybrid ansatz suggests, but does not predict, that the H-dibaryon mass may be as low as 1.5 GeV.
    -----------
    Has anyone got anything newer or informative?
     
  9. May 9, 2007 #8

    jal

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    I have assimilated the material and entered it into my blog.
    Job opening
    Writing a peer review paper intergrating H-dibaryon with LQG, Spin network and Strings with QMLS.
    jal
     
    Last edited: May 9, 2007
  10. May 21, 2007 #9

    jal

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