Neutral pion and $\eta$ meson production at mid-rapidity in Pb-Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV

TL;DR

This paper reports measurements of neutral pion and eta meson production at mid-rapidity in Pb-Pb collisions at 2.76 TeV, extending the transverse momentum range and providing new insights into suppression patterns and hadronization at the LHC.

Contribution

First measurement of eta meson production in heavy-ion collisions at the LHC and extension of neutral pion measurements to higher transverse momentum.

Findings

Similar eta/pi0 ratio at different centralities with a high-$p_{T}$ plateau.

Observed suppression of meson production in Pb-Pb relative to scaled pp collisions.

Stronger suppression at high energies compared to lower-energy experiments.

Abstract

Neutral pion and $\eta$ meson production in the transverse momentum range 1 < $p_{T}$ < 20 GeV/$c$ have been measured at mid-rapidity by the ALICE experiment at the Large Hadron Collider (LHC) in central and semi-central Pb-Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV. These results were obtained using the photon conversion method as well as the PHOS and EMCal detectors. The results extend the upper $p_{T}$ reach of the previous ALICE $\pi^{0}$ measurements from 12 GeV/$c$ to 20 GeV/$c$ and present the first measurement of $\eta$ meson production in heavy-ion collisions at the LHC. The $\eta/\pi^{0}$ ratio is similar for the two centralities and reaches at high $p_{T}$ a plateau value of 0.457 $\pm$ 0.013$^{stat}$ $\pm$ 0.018$^{syst}$. A suppression of similar magnitude for $\pi^{0}$ and $\eta$ meson production is observed in Pb-Pb collisions with respect to their production in pp collisions scaled by the number of binary nucleon-nucleon collisions. We discuss the results in terms of NLO pQCD predictions and hydrodynamic models. The measurements show a stronger suppression with respect to what was observed at lower center-of-mass energies in the $p_{T}$ range 6 < $p_{T}$ < 10 GeV/$c$. At $p_{T}$ < 3 GeV/$c$, hadronization models describe the $\pi^{0}$ results while for the $\eta$ some tension is observed.