Unusual features of drell-yan diffraction

The cross section of the diffractive Drell-Yan (DY) process, pp{yields}llXp, where the system llX is separated by a large rapidity gap from the recoil proton, is calculated in the light-cone dipole approach. This process reveals unusual features, quite different from what is known for diffractive deeply inelastic scattering (DIS) and non-Abelian radiation: (i) the diffractive radiation of a heavy dilepton by a quark vanishes in the forward direction; (ii) the diffractive production of a dilepton is controlled by the large hadronic radius; (iii) in contrast with DIS where diffraction is predominantly soft, the diffractive DY reaction is semihard-semisoft; (iv) as a result of the saturated shape of the dipole cross section, the fraction of diffractive DY events steeply falls with energy but rises as a function of the hard scale. These features are common for other Abelian bremsstrahlung processes (higgsstrahlung, Z-strahlung, etc.). Measurements of diffractive DY processes at modern colliders would be a sensitive probe for the shape of the dipole cross section at large separations.