Particle multiplicities in Lead-Lead collisions at the LHC from non-linear evolution with running coupling

TL;DR

Predictions for the pseudorapidity density of charged particles produced in central Pb-Pb collisions at the LHC are presented and the initial conditions for the evolution are fixed.

Abstract

We present predictions for the pseudo-rapidity density of charged particles produced in central Pb-Pb collisions at the LHC. Particle production in such collisions is calculated in the framework of k_t-factorization. The nuclear unintegrated gluon distributions at LHC energies are determined from numerical solutions of the Balitsky-Kovchegov equation including recently calculated running coupling corrections. The initial conditions for the evolution are fixed by fitting RHIC data at collision energies \sqrt{s}}=130 and 200 GeV per nucleon. We obtain dN^{Pb-Pb}_{ch}/dη(\sqrt{s}=5.5 TeV, η=0)\approx 1290÷1480.

Figures (4)

• Figure 1: $\lambda\!=\!\frac{d\ln Q_s^2(Y)}{dY}$, for $Q_{0}\!=\!0.5$, 0.75, 1 and 1.25 GeV (from top to bottom), and for $\kappa\!=\!0.5$ (left) and $\kappa\!=\! e^{-1}$ (right).
• Figure 2: Pseudo-rapidity density of charged particles produced in Au-Au 0-6% central collisions at $\sqrt{s_{NN}}=130$ GeV. Data taken from rhic. The solid lines correspond to $Q_{0}\!=\!1$ GeV, $m\!=\!0.25$ GeV, $\Delta Y\!=\!1$ and $x_{1,2}\!=\!(m_t/\sqrt{s})\,e^{\pm y}$. The modifications to this central value considered are: Upper-left: $m\!=\!0.5$ GeV (dashed line) and $m\!=\!0$ GeV (dashed-dotted line). Upper-right: $\Delta Y\!=\!3$ (dashed line) and $\Delta Y\!=\!10$ (dashed-dotted line). Lower-left: $Q_{0}\!=\!0.7$ GeV, (dashed line) and $Q_{0}\!=\!1.25$ GeV, (dashed-dotted line). Lower-right: $x_{1,2}\!=\!(p_t/\sqrt{s})\,e^{\pm y}$ (dashed line).
• Figure 3: Pseudo-rapidity density of charged particles produced in Au-Au 0-6% central collisions at $\sqrt{s_{NN}}=130$ and 200 GeV and for Pb-Pb central collisions at $\sqrt{s_{NN}}=5.5$ TeV. Data taken from rhic. The upper, central (solid lines) and lower limits of the theoretical uncertainty band correspond to ($Q_{0}\!=\!1$ GeV, $\Delta Y\!=\!1$), ($Q_{0}\!=\!0.75$ GeV, $\Delta Y\!=\!3$) and ($Q_{0}\!=\!1.25$ GeV, $\Delta Y\!=\!0.5$) respectively, with $m\!=\!0.25$ GeV in all cases.
• Figure 4: Charged particle multiplicity in central Au-Au collisions at $\eta=0$ versus collision energy. Upper plot: Results obtained with the set up leading to Eq. (\ref{['pred']}) (band) and several modifications of it (see text). Lower plot: Power-law, $a\sqrt{s}^{\,b}$, and logarithmic, $a\!+\!b\ln s$, fits to RHIC data at $\sqrt{s_{NN}}=19.2$, 64.2, 130 and 200 GeV.