Scaling of transverse energies and multiplicities with atomic number and energy in ultrarelativistic nuclear collisions

TL;DR

This paper models how initial energy density and particle production in ultrarelativistic heavy ion collisions scale with atomic number and energy using the saturation momentum, linking soft and perturbative descriptions.

Contribution

It introduces a method to estimate particle production scaling based on the saturation momentum, bridging soft nonperturbative and perturbative regimes in heavy ion collisions.

Findings

Scaling relations are consistent with experimental data at RHIC and LHC energies.

Soft processes can be described using gluons and quarks via saturation physics.

Results are reasonable even at SPS energies, indicating broad applicability.

Abstract

We compute how the initial energy density and produced gluon, quark and antiquark numbers scale with atomic number and beam energy in ultrarelativistic heavy ion collisions. The computation is based on the argument that the effect of all momentum scales can be estimated by performing the computation at one transverse momentum scale, the saturation momentum. The initial numbers are converted to final ones by assuming kinetic thermalisation and adiabatic expansion. The main emphasis of the study is at LHC and RHIC energies but it is observed that even at SPS energies this approach leads to results which are not unreasonable: what is usually described as a completely soft nonperturbative process can also be described in terms of gluons and quarks. The key element is the use of the saturation scale.