Multiple Interactions and Saturation in High Energy Collisions

Energy conservation is a large part of the NLO corrections to BFKL. A formalism is presented which includes effects of energy-momentum conservation in the dipole formalism in transverse coordinate space. Energy conservation gives a very strong suppression at small x, which implies that the effect of multi-pomeron exchange and saturation are pushed to very small x-values or very high energies. Perturbative QCD and PDFs from HERA can describe jets and Et-flow in high energy pp collisions, but the multiplicity distributions are much more sensitive to non-perturbative effects. Analyses of minimum bias and underlying events show that colours appear to combine to give strings which are as short as possible, in a way very different from e+e- annihilation. This leads to important questions about the properties of the pomeron, the relation between high multiplicity events and diffraction, and the applicability of the AGK cutting rules.