Hadron multiplicities

Abstract

We review results on hadron multiplicities in high energy particle collisions. Both theory and experiment are discussed. The general procedures used to describe particle multiplicity in Quantum Chromodynamics (QCD) are summarized. The QCD equations for the generating functions of the multiplicity distributions are presented both for fixed and running coupling strengths. The mean multiplicities of gluon and quark jets, their ratio, higher moments, and the slopes of multiplicities as a function of energy scale, are among the main global features of multiplicity for which QCD results exist. Recent data from high energy e + e − experiments, including results for separated quark and gluon jets, allow rather direct tests of these results. The theoretical predictions are generally quite successful when confronted with data. Jet and subjet multiplicities are described. Multiplicity in limited regions of phase space is discussed in the context of intermittency and fractality. The problem of singularities in the generating functions is formulated. Some special features of average multiplicities in heavy quark jets are described.

A multiparton model for pp / p$\bar{p}$ inelastic scattering

“…[3] and for completeness we record here: The results demonstrate that the probability of formation of one (q (1) ) and two (q (2) ) strings are approximately constants in a wide interval of energy (10-5000 GeV). In counterpart, the probability of formation of three (q (3) ) and four (q (4) ) strings increases as √ s also increases. As each initial string created is associated with a parton-parton collision, it may indicate that the gluons and sea quarks are increasingly important in determining the characteristics of the interactions as the energy is increased.…”

Multiplicity dependence of two-particle azimuthal correlations in pp collisions at the LHC

“…Experimentally one finds that KNO scaling is violated for √ s > 200 GeV [3]. This scaling violation which increases with √ s has been interpreted as a consequence of particle production through multiple parton-parton interactions (MPI) [4][5][6]. Further, at the LHC, already at a transverse momentum transfer of a -1 -…”

Jet multiplicities as the QGP thermometer

“…They are well described by quantum chromodynamics (QCD) equations (see, e.g., reviews [1,2,3]). The jets in e + e − annihilation evolve in the QCD vacuum as a cascade process by stretching and breaking strings between color charges.…”