KNO scaling from a nearly Gaussian action for small-x gluons

Gluon saturation and initial conditions for relativistic heavy ion collisions

“…of that equation. 176 Since the mean multiplicity in the classical limit is of order n ≡ dN/dy ∼ 1/α s it follows that n/k ∼ 1/α s 1. This, in fact, corresponds to the limit where the NBD multiplicity distributions exhibit KNO scaling.…”

“…177 The semi-classical strong-field limit of a Gaussian effective theory relates the emergence of KNO scaling in p ⊥ -integrated multiplicity distributions to properties of small-x gluons around the saturation scale. 176 KNO scaling conjectures that the particle multiplicity distribution in high-energy hadronic collisions is universal (i.e., energy independent) if expressed in terms of the fractional multiplicity z ≡ n/n. This is satisfied in first approximation in the central (pseudo-) rapidity region at energies ≥ 200 GeV as shown in Fig.…”

Multiplicity distributions in the low x regime in a simple model

“…In fact, the first estimate of the mean multiplicity of produced particles in the CGC framework was done in [38] and in [39]. According to [38] (see also [29]) in the saturation regime the number of produced partons is given by…”

“…In a third group, we find works in which the authors try to build the bridge between QCD and data. In this cathegory we include the studies performed with more phenomenological models [15,16,29,30] and with event generators [3,31], which are built to reproduce all the observable quantities in a high energy collision.…”

Review of Recent Developments in the CGC

“…For a quadratic action such as in the MV model this leads (approximately) to a negative binomial distribution [13]; corrections are illustrated in ref. [14]. At midrapidity the bulk of the multiplicity distributions from p+p collisions at energies 0.2 -7 TeV can indeed be described quite well by NBDs [9,15] Figure 2: KNO scaling plot of charged particle multiplicity distributions at |η| < 0.5 in NSD collisions at various energies [16] and NBD fits; z ≡ N ch / N ch and Ψ(z) ≡ N ch P(N ch ).…”