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CALSCALE:GREGORIAN
PRODID:UW-Madison-Physics-Events
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SEQUENCE:0
UID:UW-Physics-Event-1613
DTSTART:20091105T220000Z
DURATION:PT1H0M0S
DTSTAMP:20260506T172206Z
LAST-MODIFIED:20091102T171848Z
LOCATION:5310 Chamberlin
SUMMARY:The Baryon Resonance Spectrum and the 1/Nc Expansion\, NPAC (N
 uclear/Particle/Astro/Cosmo) Forum\, Richard Lebed\, Arizona State Uni
 versity
DESCRIPTION:Why do baryon resonance multiplets exist\, and what contro
 ls their formation and decays?  It is natural to consider them as mere
 ly excited states of some three-quark or meson-nucleon potential. But 
 these are just simplistic quantum-mechanical pictures that recognize n
 either the full field-theoretical complexities of QCD nor the extremel
 y brief lifetimes of resonances due to quark pair production. Both of 
 these issues are addressed by the 1/Nc expansion of QCD\, where Nc is 
 the number of color charges. Constraints arising at large Nc on meson-
 baryon scattering amplitudes not only create linear relationships betw
 een them\, thus linking distinct partial waves and their embedded reso
 nances\, but also restrict the possible resonant decay channels.  I pr
 esent strong experimental evidence in favor of this approach\, describ
 e the multiplet structure that it predicts\, and show how to perform t
 he analysis beyond the strict large Nc limit by incorporating 1/Nc-sup
 pressed effects.  This program has been developed to the point that no
 w one possesses a full effective field theory formalism for physics in
  the baryon resonance region.
URL:https://www.physics.wisc.edu/events/?id=1613
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