  We evaluate, in a model-independent way, the signal-to-background ratio for
Higgs -> b bbar detection in exclusive double-diffractive events at the
Tevatron and the LHC. For the missing-mass approach to be able to identify the
Higgs boson, it will be necessary to use a central jet detector and to tag b
quark jets. The signal is predicted to be very small at the Tevatron, but
observable at the LHC. However we note that the background, that is
double-diffractive dijet production, may serve as a unique gluon factory. We
also give estimates for the double-diffractive production of chi_c and chi_b
mesons at the Tevatron. We emphasize that a high-resolution missing-mass
measurement, on its own, is insufficient to identify rare processes.
