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Aidan Randle-Conde | Université Libre de Bruxelles | Belgium

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Advent Calendar 2012 December 5th

5 is for pentaquarks, the exotic baryons that got discovered and then undiscovered!
Slides taken from Pat Burchat’s excellent talk on pentaquarks: https://www.stanford.edu/dept/physics/people/faculty/docs/burchatUCIseminar.pdf
Fake peak plot from paper by Torres and Oset: http://arxiv.org/abs/1012.2967
The Particle Data Group (PDG) review on pentaquarks (PDF documents) 2008, 2006, 2004.

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  • Amir Livne Bar-on

    Can you elaborate a little more about the theoretical predictions of pentaquarks?

    I don’t know that the relevant theory for describing them is, but let’s assume for a moment it’s QCD. So do QCD calculations and simulations show that these particles exist? Is this kind of question beyond our computational ability? Or can we compute it, but get the result that they don’t exist? (In this case pentaquarks would probably be a sign for new physics, right?)

  • http://aidanatcern.wordpress.com Aidan Randle-Conde

    Hi Amir, sorry for the late reply, I’ve been snowed under (quite literally!) One of the earliest papers comes from 1979 (http://prd.aps.org/abstract/PRD/v20/i3/p748_1) For some recent papers take a look at http://arxiv.org/abs/hep-ph/0307341 and http://arxiv.org/abs/hep-ph/0402260 . These papers assign spin and color correlations to estimate the bindings and masses. I’m not a QCD expert at all, so I can’t really comment much on the details of all this, but the papers should give you a good start on the basics. From what I understand about the dynamics of a baryon we don’t actually have a very good model of the inside of the proton or neutron. We know what the observables are (spin, mass, dipole moment) but actually predicting those from the partons is very difficult. Recent results from COMPASS show that most of the spin of the proton does not come from the valence quarks, so understanding how the spins work in the proton can go a long way to help us understanding what states are and are not allowed in exotic baryons.