$\pi^0$ and $\eta$ meson production in proton-proton collisions at $\sqrt{s}=8$ TeV

TL;DR

This paper reports measurements of neutral pion and eta meson production in proton-proton collisions at 8 TeV, comparing results with theoretical models and exploring the universality and scaling behaviors of meson production ratios.

Contribution

First measurement of $ m extit{invariant differential cross sections}$ for $ m extit{ extbf{ extpi}^0}$ and $ m extit{ extbf{ exteta}}$ mesons at 8 TeV, with detailed comparison to QCD calculations and event generators.

Findings

NLO pQCD overestimates cross sections but matches $ m extit{ extbf{ exteta}}/ extbf{ extpi}^0$ ratio within uncertainties.

PYTHIA 8.2 with Monash 2013 tune best reproduces measured spectra.

Universal $ m extit{ extbf{ exteta}}/ extbf{ extpi}^0$ ratio observed across different energies.

Abstract

An invariant differential cross section measurement of inclusive $\pi^{0}$ and $\eta$ meson production at mid-rapidity in pp collisions at $\sqrt{s}=8$ TeV was carried out by the ALICE experiment at the LHC. The spectra of $\pi^{0}$ and $\eta$ mesons were measured in transverse momentum ranges of $0.3<p_{\rm T}<35$ GeV/$c$ and $0.5<p_{\rm T}<35$ GeV/$c$, respectively. Next-to-leading order perturbative QCD calculations using fragmentation functions DSS14 for the $\pi^{0}$ and AESSS for the $\eta$ overestimate the cross sections of both neutral mesons, although such calculations agree with the measured $\eta/\pi^{0}$ ratio within uncertainties. The results were also compared with PYTHIA~8.2 predictions for which the Monash~2013 tune yields the best agreement with the measured neutral meson spectra. The measurements confirm a universal behavior of the $\eta/\pi^{0}$ ratio seen for NA27, PHENIX and ALICE data for pp collisions from $\sqrt{s}=27.5$ GeV to $\sqrt{s}=8$ TeV within experimental uncertainties. A relation between the $\pi^{0}$ and $\eta$ production cross sections for pp collisions at $\sqrt{s}=8$ TeV is given by $m_{\rm T}$ scaling for $p_{\rm T}>3.5$ GeV/$c$. However, a deviation from this empirical scaling rule is observed for transverse momenta below $p_{\rm T}<3.5$ GeV/$c$ in the $\eta/\pi^0$ ratio with a significance of $6.2\sigma$.