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

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.

Opportunities for heavy-ion physics at the large hadron collider LHC

“…Similar values are also obtained by invoking other mechanisms to tame the perturbative growth [10]. They are significantly higher than extrapolations of the apparently universal trends shown in Fig.…”

Ultrarelativistic Nucleus–Nucleus Collisions and the Quark–Gluon Plasma

“…The ( √ s N N ) 0.3 dependences allow for simple, experimentally-based, extrapolations to the LHC energy (of course, surprises are eagerly awaited). We note that power-law dependences are predicted by the (QCD-inspired) saturation model [37], but they are steeper (exponent 0.41, in case of dN ch /dy). The steep decrease of particle multiplicities towards the lower end of the AGS energy range reflects mainly the threshold in the overall particle production, but may indicate a change in physics as well.…”

Alice

“…It provides a good fit to data up to 200 GeV, and predicts N ch = 9 x 170= 1500 at LHC. The long dashed line is an extrapolation to LHC energies using a saturation model [20].…”