Multiple interactions, diffraction, and the BFKL pomeron

In high energy pp scattering the inclusive cross section for minijet production is very large. Unitarity then implies a high probability for multiple interactions, and a large diffractive cross section. As the proton has a substructure in terms of parton cascades, the diffraction is not only elastic, but has a large component of diffractive excitation. The cascades can fill the whole rapidity range between projectile and target, and in the Good-Walker formalism the diffractive excitation is determined by the fluctuations in the evolution. Within the Lund Dipole Cascade model, it is in this way possible to reproduce diffractive excitation in pp collisions and DIS. The result shows a multi-regge behavior, with a bare pomeron pole with α(0) = 1.21, α' = 0.2 GeV ^-2 , and an almost constant triple-pomeron coupling g _3P ≈ 0.3 GeV ^-1 . It is also pointed out that the classification of diffractive events varies between different formalisms, and cannot be uniquely defined. Therefore it is recommended to study gap events rather than diffractive events. The results presented in this talk are obtained in collaboration with Christoffer Flensburg and Leif Lönnblad.