Semihard processes in QCD

L. V. Gribov, E. M. Levin, M. G. Ryskin

Research output: Contribution to journalReview articlepeer-review

Abstract

Deep inelastic scattering, large pt particle production in hadron collisions and e+e- annihilation into hadrons are studied in perturbative QCD in the semihard region of very small x (x ≪ 1) and large Q2(pt2). At small x the parton densities increase rapidly, so that the effects of parton-parton interactions (screenings), that stop the increase of the cross sections near their unitarity limit, and the coherent emission of soft gluons by the global colour charge of whole groups of harder particles, become essential. These effects are studied in detail. It is shown that at very small x ∼ xb(Q2) (In(1/xb) ∼ αs-2(Q2)) semihard processes acquire some features essential of soft processes. Their cross sections reach values comparable to the geometrical dimensions of hadrons. At very high energies gluon jets with large pt(pt ∼ Λ exp(1.78√In √s)), (x ∼ xb) are emitted in abundance and become the main source of secondary hadrons. In e+e- annihilation the coherence of soft gluon emission leads to a dip in the inclusive spectra at small x. The colour correlations in jets and the preconfinement effects are discussed. A convenient technique for calculating and summing leading log diagrams with two logarithmically large parameters (In 1/x and In Q2) is presented. A reggeon-type diagram technique is developed to take into account parton-parton interactions. A special chapter is devoted to the phenomenology of semihard processes, in particular to large pt production at the SPS Collider energy and to large Et processes. The possible applications of perturbative QCD to soft processes are sketched.

Original languageEnglish
Pages (from-to)1-150
Number of pages150
JournalPhysics Reports
Volume100
Issue number1-2
DOIs
StatePublished - Nov 1983
Externally publishedYes

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