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

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.

27 pages, 8 captioned figures, 3 tables, authors from page 23, published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/4203