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 sqrt(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 sqrt(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.