Abstract
We show that in order to obtain a successful description of the transverse momenta distribution for charged particles in ion-ion collisions, one must include a thermal emission term. The temperature of this emission $T_{\rm th}$ turns out to be proportional to the saturation scale, $T_{\rm th} = 1.8/2\pi \,Q_s$. The formalism for the calculation of the transverse momenta spectra in CGC/saturation approach is developed, in which two stages of the process are seen: creation of the colour glass condensate, and hadronization of the gluon jets. Our calculations are based on the observation that even for small values of $p_T$, the main contribution in the integration over the dipole sizes stems from the kinematic region in vicinity of the saturation momentum, where theoretically, we know the scattering amplitude. Non-perturbativ corrections need to be included in the model of hadronization. This model incorporates the decay of a gluon jet with effective mass $m^2_{\rm eff} = 2 Q_s \mu_{\rm soft}$ where $\mu_{\rm soft}$ denotes the soft scale, with the fragmentation functions at all values of the transverse momenta. We use the KLN model which, provides a simple way to estimate the cross sections for the different centrality classes. Comparing the results of this paper with the transverse distribution in the proton-proton scattering, we see two major differences. First, a larger contribution of the thermal radiation term is needed, in accord with higher parton densities of the produced colour glass condensate. Second, even changing the model for the hadronization, without a thermal radiation term, we fail to describe the $p_T$ spectrum. Consequently, we conjecture that theexistence of the thermal radiation term is independent of the model of confinement.
Highlights
In this paper we continue to discuss the processes of multi-particle generation at high energy, in the framework of the color glass condensate (CGC)/saturation approach
Our calculations are based on the observation that even for small values of pT, the main contribution in the integration over the dipole sizes stems from the kinematic region in the vicinity of the saturation momentum, where theoretically, we know the scattering amplitude
The main result of the paper is that we show that a thermal emission term is required to describe the transverse momenta distribution for charged particles in ion-ion collision
Summary
In this paper we continue to discuss the processes of multi-particle generation at high energy, in the framework of the color glass condensate (CGC)/saturation approach (see Ref. [1] for the review). The goal of this paper is to revisit the process of inclusive production in the CGC/saturation approach, for more thorough consideration, and to show that the thermal term with the temperature given by Eq (1), is needed for describing the experimental data for ion-ion collisions at high energies. At first sight, it looks as we are pushing at an open door, since it has been shown [12,15,16,17,18,19] that the experimental data [6,20,21,22,23,24] at high energy both for hadron-hadron and ion-ion scattering, can be described as the sum of two terms: dσ dyd2pT. In the CGC approach it should be calculated theoretically, and not be determined by a fitting procedure
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