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

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 $0.3<p_{\mathrm{T}}<35$ GeV/$c$ and $0.5<p_{\mathrm{T}}<35$ 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 $\eta \mathrm{/}{\pi }^0$ 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 $\eta \mathrm{/}{\pi }^0$ 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 $m_{\mathrm{T}}$ scaling for $p_{\mathrm{T}}>3.5$ GeV/$c$. However, a deviation from this empirical scaling rule is observed for transverse momenta below $p_{\mathrm{T}}<3.5$ GeV/$c$ in the $\eta \mathrm{/}{\pi }^0$ ratio with a significance of $6.2\sigma$.