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Since protons are not spherical, are their charge fields non-spherical?

  1. Oct 8, 2009 #1

    jaketodd

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  3. Oct 8, 2009 #2

    alxm

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    (Oh USA Today, great source.)

    Yes, they're talking about a non-spherical charge distribution.

    But it's by no means generally accepted as fact that proton's aren't spherical. Those JLab results http://link.aps.org/doi/10.1103/PhysRevC.77.015202" [Broken].

    Yes, a molecule does not usually have a spherical charge distribution, since molecules aren't usually spherical, to begin with.
     
    Last edited by a moderator: May 4, 2017
  4. Oct 8, 2009 #3
    Franz Gross' paper is not in contradiction with JLab's results. Those people work at JLab ! What their paper say is that the form factors they calculate are not constrained by angular momentum. On the other hand, it is pretty well established that the densities of polarized quarks in polarized nucleons (both longitudinally and transversally) are not spherical, and that those observables are sensitive to angular momentum. We understand that from general theoretical arguments, and this is very well reproduced on the lattice.

    Once again, it is unfortunate that public relation echos are often deformed from the original message.
     
  5. Oct 9, 2009 #4

    Vanadium 50

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    I'm not quite sure what the actual result was before the media mangled it, but will nonetheless try and answer the OP.

    At small distances, the proton charge distribution is quite lumpy - quarks carry charge and at small distances you can see quarks. At large distances, the field is spherical. The proton has an electric monopole moment (i.e. charge). It has no dipole moment, and QM forbids it from having a quadrupole or higher moment. So it's spherical.
     
  6. Oct 9, 2009 #5

    jaketodd

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    Thank you! What's the minimum distance to make it spherical?
     
  7. Oct 9, 2009 #6
    Just to give justice to the original work that was quoted in the article
    Densities, Parton Distributions, and Measuring the Non-Spherical Shape of the Nucleon
    Phys.Rev.C76:065209,2007

    One may dismiss the question, or one may try to understand what is meant. Of course the proton is spherical on average. But it also sometimes looks like a pretzel when one selects certain combinations of spins for the quark and the proton. If you attended current conference on this research, you would actually hear the term "pretzelosity".

    See also for instance fig. 4 in Transverse spin structure of the nucleon from lattice QCD simulations
     
    Last edited: Oct 9, 2009
  8. Oct 9, 2009 #7

    jaketodd

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    How far Vanadium 50? Thanks.
     
  9. Oct 9, 2009 #8

    alxm

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    Well, I didn't say it was. But it seems to me there is (or was?) some disagreement about which model fit the data better, and whether the models were 'spherical' or not, judging by e.g. http://link.aps.org/doi/10.1103/PhysRevC.73.015203" [Broken] by Miller.

    I dunno, maybe it all boils down to how you define 'spherical'.
     
    Last edited by a moderator: May 4, 2017
  10. Oct 9, 2009 #9
    I hope their result has nothing to do with the positive charge atomic form-factor since the latter depends on the atomic wave function.
     
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