Quarkonium Interactions in Hadronic Matter

The cross section for the \J~and \U~interaction with light hadrons is calculated in short-distance QCD, based on the large heavy quark mass and the resulting large energy gap to open charm or beauty. The low energy form of the cross section is determined by the gluon structure functions at large $x$; hence it remains very small until quite high energies. This behaviour is experimentally confirmed by charm photoproduction data. It is shown to exclude \J~absorption in confined hadronic matter of the size or density attainable in nuclear collisions; in contrast, the harder gluon spectrum in deconfined matter allows break-up interactions.