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_{ text{ T }} <35 text{ GeV/c } and 0.5<p_{ text{ T }} <35 text{ 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_{ text{ T }} scaling for p_{ text{ T }} >3.5 text{ GeV/c }. However, a deviation from this empirical scaling rule is observed for transverse momenta below p_{ text{ T }} <3.5 text{ GeV/c } in the eta /pi ^0 ratio with a significance of 6.2sigma .
Highlights
Measuring identified particle production in proton-proton collisions over wide kinematic ranges is considered an informative probe of strong interactions at high energies
The acceptance uncertainty is estimated by changing the good cluster selection criteria, and the Monte Carlo (MC) generator-dependent uncertainty is evaluated by comparing efficiencies of minimum bias (MB) MC generators and single particle MC simulation which generates events containing single neutral mesons with realistic transverse momentum and rapidity distributions
Where Nπ0(η) is the number of reconstructed π0(η) meson in a given pT bin, Nsπe0c represents the estimated number of secondary π0 mesons, Lint is the integrated luminosity, A·εrec is the product of the geometrical acceptance and reconstruction efficiency, referred to as ε in Fig. 5, Brπ0(η)→γγ is the branching ratio for the two-gamma decay channel and ∆y∆pT is the bin width in rapidity and transverse momentum
Summary
Measuring identified particle production in proton-proton (pp) collisions over wide kinematic ranges is considered an informative probe of strong interactions at high energies. Recent progress in comprehensive global QCD analysis of parton-topion fragmentation functions at next-to-leading order (NLO) [8] derived from inclusive pion production in semi-inclusive electron-positron annihilation, deep-inelastic scattering and pp collisions over a wide energy range, including the including the LHC results latest measurements of π0. The majority of particles at low transverse momenta, pT, are produced in “soft” processes involving a small Q2 In this regime, the pQCD calculations are not applicable for description of the production mechanisms and phenomenological models are based on previous measurements of neutral meson production cross sections or other light mesons by other experiments at lower collision energies. Precise measurements of identified hadron spectra over wide transverse momentum ranges at different LHC energies are of particular importance for the quantitative description of particle production at the LHC.
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