High-energy cosmic rays are observed indirectly by detecting the extensive air showers initiated in Earth’s atmosphere. The interpretation of these observations relies on accurate models of air ...shower physics, which is a challenge and an opportunity to test QCD under extreme conditions. Air showers are hadronic cascades, which give rise to a muon component through hadron decays. The muon number is a key observable to infer the mass composition of cosmic rays. Air shower simulations with state-of-the-art QCD models show a significant muon deficit with respect to measurements; this is called the Muon Puzzle. By eliminating other possibilities, we conclude that the most plausible cause for the muon discrepancy is a deviation in the composition of secondary particles produced in high-energy hadronic interactions from current model predictions. The muon discrepancy starts at the TeV scale, which suggests that this deviation is observable at the Large Hadron Collider. An enhancement of strangeness production has been observed at the LHC in high-density events, which can potentially explain the puzzle, but the impact of the effect on forward produced hadrons needs further study, in particular with future data from oxygen beam collisions.
In detailed air shower simulations, the uncertainty in the prediction of shower observables for different primary particles and energies is currently dominated by differences between hadronic ...interaction models. With the results of the first run of the LHC, the difference between post-LHC model predictions has been reduced to the same level as experimental uncertainties of cosmic ray experiments. At the same time new types of air shower observables, like the muon production depth, have been measured, adding new constraints on hadronic models. Currently no model is able to consistently reproduce all mass composition measurements possible within the Pierre Auger Observatory for instance. Comparing the different models, and with LHC and cosmic ray data, we will show that the remaining open issues in hadronic interactions in air shower development are now in the pion-air interactions and in nuclear effects.
The interpretation of EAS measurements strongly depends on detailed air shower simulations. CORSIKA is one of the most commonly used air shower Monte Carlo programs. The main source of uncertainty in ...the prediction of shower observables for different primary particles and energies is currently dominated by differences between hadronic interaction models even after recent updates taking into account the first LHC data. As a matter of fact the model predictions converged but at the same time more precise air shower and LHC measurements introduced new constraints. Last year a new generation of hadronic interaction models was released in CORSIKA. Sibyll 2.3c and DPMJETIII.17-1 are now available with improved descriptions of particle production and in particular the production of charmed particles. The impact of these hadronic interaction models on air shower predictions are presented here and compared to the first generation of post-LHC models, EPOS LHC and QGSJETII-04. The performance of the new models on standard air shower observables is derived. Due to the various approaches in the physics treatment, there are still large differences in the model predictions but this can already be partially resolved by comparison with the latest LHC data.
In detailed air shower simulations, the uncertainty in the prediction of shower observables for different primary particles and energies is currently dominated by differences between hadronic ...interaction models. With the results of the first run of the LHC, the difference between post-LHC model predictions has been reduced to the same level as experimental uncertainties of cosmic ray experiments. At the same time new types of air shower observables, like the muon production depth, have been measured, adding new constraints on hadronic models. Currently no model is able to consistently reproduce all mass composition measurements possible within the Pierre Auger Observatory for instance. Comparing the different models, and with LHC and cosmic ray data, we will show that the remaining open issues in hadronic interactions in air shower development are now in the pion-air interactions and in nuclear effects.
Currently the uncertainty in the prediction of shower observables for different primary particles and energies is dominated by differences between hadronic interaction models. The LHC data on minimum ...bias measurements can be used to test Monte Carlo generators and these new constraints will help to reduce the uncertainties in air shower predictions. In this article, after a short introduction on air showers and Monte Carlo generators, we will show the results of the comparison between the updated version of high energy hadronic interaction models EPOS LHC and QGSJETII-04 with LHC data. Results for air shower simulations and their consequences on comparisons with air shower data will be discussed.
► 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.
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.
The pythia 6 Monte Carlo (MC) event generator, commonly used in collider physics, is interfaced for the first time with a fast transport simulation of a hydrogen atmosphere, with the same density as ...air, in order to study the properties of extended atmospheric showers (EAS) produced by cosmic-ray protons with energies -1020 eV. At variance with the hadronic MC generators (epos-lhc, qgsjet, and sibyll) commonly used in cosmic-ray physics, pythia includes the generation of harder hadronic jets and heavy (charm and bottom) quarks, thereby producing higher transverse momentum final particles, that could explain several anomalies observed in the data. The electromagnetic, hadronic, and muonic properties of EAS generated with various settings of pythia 6, tuned to proton-proton data measured at the LHC, are compared to those from epos-lhc, qgsjet 01, qgsjet-ii-04, and sibyll 2.1. Despite their different underlying parton dynamics, the characteristics of the EAS generated with pythia 6 are in between those predicted by the rest of the MC generators. The only exceptions are the muonic components at large transverse distances from the shower axis, where pythia predicts more activity than the rest of the models. Heavy-quark production, as implemented in this study for a hydrogen atmosphere, does not seem to play a key role in the EAS muon properties, pointing to nuclear effects as being responsible for the muon anomalies observed in the air-shower data.
Currently the uncertainty in the prediction of shower observables for different primary particles and energies is dominated by differences between hadronic interaction models. The LHC data on minimum ...bias measurements can be used to test Monte Carlo generators and these new constraints will help to reduce the uncertainties in air shower predictions. In this article, after a short Introduction on air showers we will show the results of the comparison between the updated version of high energy hadronic interaction models EPOS LHC and QGSJETII-04 with LHC data. Results for air shower simulations and their consequences on comparisons with air shower data will be discussed.
PDF
