Isoscalar diffractive photoproduction: A source of gluonium

Data on diffractive photoproduction of isoscalar states appear to be anomalously large in a number of channels. Isoscalar diffractive photoproduction is studied in a model in which the pomeron is approximated by two gluons, and in which gluon intermediate states are allowed in the pomeron-meson interaction. It is shown that the model allows a resolution of the long-standing problem of the small (in vector meson dominance terms) diffractive θ photoproduction cross section. This sets the scale for the calculation, and it is then demonstrated that the model can explain the large isoscalar cross section if it is due primarily to the diffractive photoproduction of a system of gluons.