Constraints from the first LHC data on hadronic event generators for ultra-high energy cosmic-ray physics

The determination of the primary energy and mass of ultra-high-energy cosmic-rays (UHECR) generating extensive air-showers in the Earth’s atmosphere, relies on the detailed modeling of hadronic multiparticle production at center-of-mass (c.m.) collision energies up to two orders of magnitude higher than those studied at particle colliders. The first Large Hadron Collider (LHC) data have extended by more than a factor of three the c.m. energies in which we have direct proton–proton measurements available to compare to hadronic models. In this work we compare LHC results on inclusive particle production at energies s=0.9,2.36, and 7 TeV to predictions of various hadronic Monte Carlo (MC) models used commonly in cosmic-ray (CR) physics (qgsjet, epos and sibyll). As a benchmark with a standard collider physics model we also show pythia (and phojet) predictions with various parameter settings. While reasonable overall agreement is found for some of the MC, none of them reproduces consistently the s evolution of all the observables. We discuss implications of the new LHC data for the description of cosmic-ray interactions at the highest energies.

► In this work we compare results on inclusive particle production at center-of-mass (c.m.) energies sqrt (s) = 0.9, 2.36, and 7 TeV measured in proton–proton collisions at the CERN Large Hadron Collider to the predictions of various hadronic Monte Carlo (MC) models (QGSJET, EPOS and SIBYLL) used commonly in ultra-high-energy cosmic-ray physics.
► As a benchmark with standard collider physics hadronic models we also show data-theory comparisons using the PYTHIA and PHOJET MCs with various parameter settings.
► While reasonable overall agreement is found for some of the MC, none of them reproduces consistently the sqrt (s) evolution of all the inclusive hadron observables.
► We discuss implications of the new LHC data for the description of cosmic-ray interactions at the highest energies measured on Earth.