Consequences of the Heavy Quark Symmetry for Semileptonic Decays of Heavy Baryons

Abstract

The properties of QCD in the infinite quark mass limit are currently the subject of intense study. It has been shown (Isgur and Wise, 1989, 1990, 1991) that in the formal limit of infinitely large momenta and masses of the heavy quarks, where the momentum-mass ratios, i.e. the velocities, are kept fixed, a new spin-flavour symmetry emerges. In fact it is a SU(2) S ⊗ SU(2) F symmetry if we restrict ourselves to c and b quarks. This symmetry is termed the heavy quark symmetry (HQS). Like the usual SU(3) flavour symmetry of the three light quarks the HQS has a lot of phenomenological consequences. For example, it leads to relations between the form factors of weak decay processes such as or determines ratios of heavy hadron cross sections. It has also been realized that the HQS leads to a precise determination of the Kobayashi-Maskawa matrix element V bc . No crucial experimental test of the heavy quark symmetry exists as yet. In the near future, however, sufficient data will have been accumulated (ARGUS, CLEO, LEP) in order to examine the symmetry propositions.