Energy Flow Observables

A few comments are made on the role of nonperturbative and perturbative power corrections. This is followed by a description of energy flow observables and correlations that may provide a flexible approach to rapidity distributions in hadronic scattering. 1 From Factorized Cross Sections to Classical Fields This short talk describes a modest attempt to synthesize one or two of the ideas exchanged at this stimulating workshop. I will try to connect two themes relevant to the very highest energy collisions, the saturation scale and rapidity distributions, with perturbative QCD for hard-scattering cross sections. The very high energies observed in cosmic ray collisions make it natural to think of perturbative QCD, but of course momentum transfers are by no means asymptotically large in most inelastic collisions in the upper atmosphere [1], or at accelerators for that matter. At extemely high energies, however, the same Lorentz contractions of the target and projectile that are at the basis of factorization may also result in very high effective field strengths, which can provide a new dynamical energy, referred to as the saturation scale [2]. The saturation scale acts in a sense as a mean momentum transfer for all partons in the dense medium. For high enough densities and energies, it can be well into the perturbative region. We can ask how Based on a talk presented at the 44th INFN Workshop, “QCD at Cosmic Energies”, Aug.29 Sept.5, 2004, Erice, Italy.