Light neutral-meson production in pp collisions at √s=13 TeV

Abstract

The momentum-differential invariant cross sections of pi(0) and eta mesons are reported for pp collisions at root s = 13 TeV at midrapidity (vertical bar y vertical bar < 0.8). The measurement is performed in a broad transverse-momentum range of 0.2 < p(T) < 200 GeV/c and 0.4 < p(T) < 60 GeV/c for the pi(0) and eta, respectively, extending the p(T) coverage of previous measurements. Transverse-mass-scaling violation of up to 60% at low transverse momentum has been observed, agreeing with measurements at lower collision energies. Transverse Bjorken x (x(T)) scaling of the pi(0) cross sections at LHC energies is fulfilled with a power-law exponent of n = 5.01 +/- 0.05, consistent with values obtained for charged pions at similar collision energies. The data are compared to predictions from next-to-leading order perturbative QCD calculations, where the pi(0) spectrum is best described using the CT18 parton distribution function and the NNFF1.0 or BDSS fragmentation function. Expectations from PYTHIA8 and EPOS LHC overestimate the spectrum for the pi(0) and are not able to describe the shape and magnitude of the eta spectrum. The charged-particle multiplicity dependent pi(0) and eta p(T) spectra show the expected change of the spectral shape, characterized by a flatter slope with increasing multiplicity. This is demonstrated across a broad transverse-momentum range and up to events with a charged-particle multiplicity exceeding five times the mean value in minimum bias collisions. The eta/pi(0) ratio depends on the charged-particle multiplicity for p(T) < 4 GeV/c. PYTHIA8 and EPOS LHC qualitatively explain this behavior with an increasing contribution from the feed-down of heavier particles to the pi(0) spectrum.