Transverse structure of strong interactions at LHC: From diffraction to new particle production

Abstract

We discuss the global structure of pp events at LHC with hard processes (particle production in two-parton collisions) on the basis of the transverse spatial characteristics of the partonic initial state. Studies of hard exclusive processes in ep scattering have shown that the transverse area occupied by partons with x >= 10^{-2} is much smaller than the size of the nucleon as it appears in generic inelastic pp collisions at high energies ("two-scale picture"). We show that this is consistent with the observation that the elastic pp amplitude at the Tevatron energy is close to the black body limit at small impact parameters. Our picture implies that inclusive heavy particle production (Higgs, SUSY) happens only in central pp collisions. At LHC energies, the final state characteristics of such events are strongly influenced by the approach to the black body limit, and thus may differ substantially from what one expects based on the extrapolation of Tevatron results. Our two-scale picture also allows us to analyze several types of hard diffractive processes observable at LHC: i) Diffractive proton dissociation into three jets, which probes small-size configurations in the proton wave function; ii) exclusive diffractive Higgs production, in which we estimate the rapidity gap survival probability; iii) inclusive diffractive processes.