BLED WORKSHOPS
IN PHYSICS
VOL. 1, NO. 1
Proceedins of the Mini-Workshop
Few-Quark Problems (p. 28)
Bled, Slovenia, July 8-15, 2000
Heavy Baryons, Solitons and LargeN
 QCD or A
New Emergent Symmetry of QCD
Thomas D. Cohen?
Department of Physics, University of Maryland, College Park, 20742-4111, USA.
In this talk I describe some recent work with C. K. Chow on heavy baryons—
i.e. baryons with a single heavy quark. In the combined heavy quark and largeN
 limits of QCD a simple physical picture emerges of such states. The system is
well described by the collective motion of the light quark and gluon degrees of
freedom against the heavy quark. This can be shown by studying commutators of
collective operators with the QCD Hamiltonian in the context of a power count-
ing scheme in which both the heavy quark and the nucleon mass is treated as
heavy. The power counting parameter is  where   =MQ; ; 1=N
. Collective
excitations have an energy which scale as 1=2 and hence all become degener-
ate with the ground state in this combined limit—this indicates the emergence
of a new symmetry. This new symmetry is contracted O(8) and is the spectrum
generating algebra for the three dimensional harmonic oscillator. One can exploit
this symmetry to make model independent predictions of excited state masses,
electro-magnetic and weak transitions of these states up to a fixed order in the
expansion. Unfortunately, the expansion turns out to be in 1=2 rather than  so
the predictive power of this expansion is not clear. However at next-to-leading
order the expansion has only two parameters and several observables (of which
only one has presently been measured) so that the possibility of getting semi-
quantitative information from this expansion is quite real.
? E-mail: cohen@physics.umd.edu