High energy hadron collisions in QCD

Abstract

In this review we present the microscopic approach to large cross section physics at high energy, based on the leading logarithmic approximation of perturbative QCD and the reggeon diagram technique. We insist that at high energy the main source of secondary hadrons is the production and fragmentation of the gluon minijets with transverse momentum q t ≈ q 0, which rapidly growswith energy, namely q 2 t≈ q 2 0≈Λ 2 exp(2.5√ln s). Such a large value of the transverse momentum allows us to adopt perturbative QCD for high hadron collisions. The completely avoid the unknown confinement problem, a new scale Q 0 ( Q 0≈1 GeV, α s( Q 2 0)<1) is introduced in our calculations and only momenta q t> Q 0 for gluons are taken into account in any integration. All our results only slightly depend on the value of Q 0. It is shown that perturbative QCD is able to describe the main properties of the hedron interactions at high energy, namely, the inclusive spectra of secondary hadrons as functions of y and q t, including small q t⪅300MeV, in a wide energy range √ s=50–900 GeV, the multiplicity distribution, the mean transverse momentum versus multiplicity and so on. We use only three phenomenological parameters in such a description of the experimental data; these values are in agreement with theoretical estimates. Our approach predicts a rapid increase of the mean transverse momentum for secondary hadrons, q t≈ q 0, where q 0=2.5 GeV at √ S=0.5 TeV, and q 0⋍7 GeV at √ S=40 TeV, the total multiplicity N≈ q 2 0, the total cross section σ t≈ln 2 s and a comparatively slow increase of the diffraction dissociation cross section σ D≈ln s.