Splitting the pomeron into two jets: a novel process at HERA

We study a novel property of large rapidity-gap events in deep inelastic scattering at HERA: splitting the pomeron into two jets in the photon-pomeron fusion reaction $\gamma^{*}\Pom \rightarrow q\bar{q}$. It gives rise to the diffraction dissociation of virtual photons into the back-to-back jets. We find that at large invariant mass $M$ of two jets, $M^{2}\gg Q^{2}$, the transverse momentum of jets comes from the intrinsic transverse momentum of gluons in the pomeron, and the photon-pomeron fusion direcly probes the diffrential gluon structure function of the proton $\partial G(x,q^{2})/\partial \log q^{2}$ at the virtuality $q^{2}\sim k^{2}$. We present estimates for the jet production cross section, which show the process is easily measurable at HERA.