Implications of isospin conservation in Λb decays and lifetime

We consider isospin predictions for the semi-leptonic and non-leptonic decays of the Λb baryon. Isospin conservation of the strong interactions constrains the possible final states in Λb decays. Since the baryon hyperfine splittings depend upon light quark dynamics and do not decrease with increasing heavy quark mass, this leads in general to to phase space enhancements in Λb decays relative to B meson decays for the same underlying quark transitions. Consequently the Λb lifetime is smaller than the B lifetime. Phase space enhancements in Λb decays relative to B decays can be understood in terms of hyperfine interactions in the heavy quark system.