The production in hadron collisions of a pair of virtual photons, each having a large invariant mass, proceeds via two mechanisms: (a) two independent Drell-Yan-type annihilations of quark pairs in a single interaction and (b) the pair annihilation process $q\overline{q}\to {\gamma }^{*}{\gamma }^{*}$. We argue that both mechanisms allow intriguing tests of constituent structure and its associated scaling laws and we show that, despite their ${\alpha }^4$ production rate, events of this type are accessible with existing $\pi$ and proton beams.

• Received 26 December 1979

DOI:https://doi.org/10.1103/PhysRevD.22.2789