Heavy quark fluorescence

Abstract

Heavy hadrons containing heavy quarks (for example, Y mesons) feature a scale separation between the heavy-quark mass and the QCD scale that controls the effective masses of lighter constituents. As in ordinary molecules, the deexcitation of the lighter, faster degrees of freedom leaves the velocity distribution of the heavy quarks unchanged, populating the available decay channels in qualitatively predictable ways. Automatically an application of the Franck-Condon principle of molecular physics explains several puzzling results of Y(5S) decays as measured by the Belle Collaboration, such as the high rate of B(s)*(B) over bar (s)* versus B(s)*(B) over bar (s) production, the strength of three-body B*(B) over bar pi decays, or the dip in B momentum shown in these decays. We argue that the data show the first Sturm-Liouville zero of the Y(5S) quantum-mechanical squared wave function and provide evidence for a largely b (b) over bar composition of this meson.