arXiv subjects

Felix Riehn

Publications and source records attributed to Felix Riehn.

At least 19 recordsLinked to original sources

arXiv2026

Forward hadron production in proton-air collisions above LHC energies through the fluctuations of extensive air showers

Primary proton-air interactions at ultra-high energies leave a physically interpretable imprint on the correlated fluctuations of the depth of shower maximum and the muon content in extensive air showers. This imprint reflects the stochasticity in the partition of the primary energy among secondary particles in the first interaction. We show that these fluctuations can be accessed through a probabilistic description that isolates sensitivity to hadronic physics in the initial collision, while treating the subsequent shower development as effectively universal. The uncertainties resulting from this universality are smaller than the spread among current hadronic interaction models and comparable to current experimental uncertainties. Consequently, the joint observable space defined by these two quantities provides a new probe of hadron production in kinematic regimes far beyond the reach of human-made accelerators.

astro-ph.HE↗

arXiv2025

Probabilistic mapping between multiparticle production variables and the depth of maximum in proton-induced extensive air showers

The interaction of ultra-high-energy cosmic rays with air nuclei triggers extensive air showers that reach their maximal energy deposition at the atmospheric depth $X_{\max}$. The distribution of this shower observable encodes information about the proton-air cross-section via fluctuations of the primary interaction point, $X_1$, and hadron production through $ΔX_{\max} \equiv X_{\max} - X_1$. We introduce new multiparticle production variables, $α_{\textrm{had}}$, $ζ_{\textrm{had}}$, and $ζ_{\mathrm{EM}}$, built from the energy spectra of secondaries in the primary interaction. Their linear combination, $ξ$, predicts over $50 \%$ of the fluctuations in $ΔX_{\max}$. Moreover, we build a probabilistic mapping based on the causal connection between $ξ$ and $ΔX_{\max}$ that enables model-independent predictions of $X_{\max}$ moments with biases below $3\,\mathrm{g\,cm^{-2}}$. Therefore, measurements of the distribution of $X_{\max}$ allow a data-driven probing of secondary hadron spectra from the cosmic-ray-air interaction, in proton-induced showers. The distributions of the new multiparticle production variables can be measured in rapidity regions accessible to current accelerators and are strongly dependent on the hadronic interaction model in the kinematic regions exclusive to ultra-high-energy cosmic rays.

astro-ph.HE↗

arXiv2025

Road map for the tuning of hadronic interaction models with accelerator-based and astroparticle data

In high-energy and astroparticle physics, event generators play an essential role, even in the simplest data analyses. As analysis techniques become more sophisticated, e.g. based on deep neural networks, their correct description of the observed event characteristics becomes even more important. Physical processes occurring in hadronic collisions are simulated within a Monte Carlo framework. A major challenge is the modeling of hadron dynamics at low momentum transfer, which includes the initial and final phases of every hadronic collision. QCD-inspired phenomenological models used for these phases cannot guarantee completeness or correctness over the full phase space. These models usually include parameters which must be tuned to suitable experimental data. Until now, event generators have been developed and tuned mainly on the basis of data from high-energy physics experiments at accelerators. The wealth of data available from the latest generation of astroparticle experiments has not yet been fully exploited, and in many cases is not satisfactorily described. Both kinds of data sets are complementary as astroparticle experiments provide sensitivity especially to hadrons produced nearly parallel to the collision axis and cover center-of-mass energies up to several hundred TeV, well beyond those reached at colliders so far. In this report, we provide an overview of state-of-the-art event generators and their tuning, including the most relevant inputs from high-energy accelerator and astroparticle experiments. We present a road map that shows, for the first time, how the unified tuning of event generators with accelerator-based and astroparticle data can be performed.

astro-ph.HE↗

arXiv2025

Probing hadronic interactions with high-energy and low-energy muons in extensive air showers

High-energy cosmic rays are observed indirectly by detecting the extensive air showers initiated in Earth's atmosphere. The interpretation of experimental data relies on accurate modeling of the air shower development. Simulations based on current hadronic interaction models show significant discrepancies with measurements of the muon content in air showers, commonly referred to as the Muon Puzzle, indicating severe shortcomings in the understanding of particle physics. A hybrid detector design with a surface array and deep underground detector, such as the IceCube Neutrino Observatory, allows simultaneous measurements of muons at two vastly different energies: at GeV energies and above a few 100GeV. We present phenomenological studies of low-energy and high-energy muons in simulated air showers, and discuss how hybrid measurements can provide constraints on multi-particle production in hadronic interaction models.

astro-ph.HE↗

arXiv2025

From collider to cosmic rays: Pythia 8/Angantyr for air shower simulations in CORSIKA 8

The simulation of extensive air showers is pivotal for advancing our understanding of high-energy cosmic ray interactions in Earth's atmosphere. The CORSIKA 8 framework is being developed as a modern, flexible, and efficient tool for simulating these interactions with a variety of high-energy hadronic models. We present the ongoing implementation and validation of Pythia 8/Angantyr within CORSIKA 8. Pythia 8, successfully used in collider physics, provides a detailed and well-tested treatment of hadronic interactions, while the Angantyr model extends its capabilities to describe heavy-ion collisions in a consistent manner. With the inclusion of Pythia 8, the CORSIKA 8 suite now enables further tuning possibilities, improving the exploration of hadronic interactions in air showers. In this contribution, we compare the capability of Pythia 8/Angantyr to reproduce fundamental observables of high-energy particle collisions $-$ inelastic cross-sections and multiplicities $-$ to that of several established high-energy interaction models in air shower simulations. We further compare the predictions for key air shower properties, including longitudinal shower development and muon content, for iron-induced shower.

astro-ph.HE↗

arXiv2025

Updated comparison of the UHECR energy spectra measured by the Pierre Auger Observatory and the Telescope Array

The Pierre Auger and Telescope Array joint Working Group on the UHECR energy spectrum was established in 2012 to analyze energy scale uncertainties in both experiments and to in vestigate their systematic differences, particularly in the spectral shape of the flux measurements. Previous studies have indeed shown that, within systematic uncertainties, the energy s pectra measured by the two observatories are consistent below~$10\,\mathrm{EeV}$. However, at higher energies, a significant difference remains. In this work, we re-examine this discrepan cy in greater detail and explore its possible origins. We consider systematic and statistical uncertainties, including the conversion from directly measured observables to energy and the calculation of exposures. We present an updated energy scale comparison between the two experiments and updated flux measurements in the common declination band.

astro-ph.HE↗

arXiv2025

Testing Gamma/Hadron Separation for Ultra-High-Energy Cherenkov Astronomy

Dark100 is a planned array of six telescopes, using the Panoramic Search for Extraterrestrial Intelligence (PANOSETI) telescope system. It will operate as an imaging atmospheric Cherenkov telescope array, with a telescope design and array layout optimized for accessing gamma rays with tens of TeV to PeV energies. The science goals of Dark100 include the search for ultra-heavy dark matter, observations of Galactic Pevatrons, and the search for ultra-fast optical transients. Rejection of background cosmic rays is key to the sensitivity of the array. We present a first study of gamma/hadron separation based on simulated gamma rays and protons, focusing on the impact of the hadronic background models used in CORSIKA.

astro-ph.HE↗

arXiv2025

Prompt and Conventional High-Energy Muon Spectra from a full Monte Carlo Simulation via $\texttt{CORSIKA7}$

Extensive air showers produce high-energy muons that can be utilized to probe hadronic interaction models in cosmic ray interactions. Most muons originate from pion and kaon decays, called $\textit{conventional}$ muons, while a smaller fraction, referred to as $\textit{prompt}$ muons, arises from the decay of heavier, short-lived hadrons. The $\texttt{EHISTORY}$ option of the air shower simulation tool $\texttt{CORSIKA7}$ is used in this work to investigate the prompt and conventional muon flux in the energy range of 100 TeV to 100 PeV, utilizing the newly developed open-source python software $\texttt{PANAMA}$. Identifying the muon parent particles allows for scaling the contribution of prompt particles, which can be leveraged by future experimental analyses to measure the normalization of the prompt muon flux. Obtained prompt muon spectra from $\texttt{CORSIKA7}$ are compared to $\texttt{MCEq}$ results. The relevance to large-volume neutrino detectors, such as IceCube and KM3NeT, and the connection to hadronic interaction models is discussed.

astro-ph.HE↗

arXiv2024

CORSIKA 8 with Pythia 8: Simulating Vertical Proton Showers

The field of air shower physics, dedicated to understanding the development of cosmic-ray interactions with the Earth's atmosphere, faces a significant challenge regarding the muon content of air showers observed by the Pierre Auger Observatory, and numerous other observatories. Thorough comparisons between extensive air shower (EAS) measurements and simulations are imperative for determining the primary energy and mass of ultra-high energy cosmic rays. Current simulations employing state-of-the-art hadronic interaction models reveal a muon deficit compared to experimental measurements, commonly known as the "Muon Puzzle". The primary cause of this deficit lies in the uncertainties surrounding high-energy hadronic interactions. In this contribution, we discuss the integration of a new hadronic interaction model, Pythia 8, into the effort to resolve the Muon Puzzle. While the Pythia 8 model is well-tailored in the context of Large Hadron Collider (LHC) experiments, its application in air shower studies remained limited until now. However, recent advancements, particularly in the Angantyr model of Pythia 8, offer promising enhancements in describing hadron-nucleus interactions, thereby motivating its potential application in air shower simulations. We present results from EAS simulations conducted using CORSIKA 8, wherein Pythia is employed to model hadronic interactions.

astro-ph.HE↗

arXiv2024

Proton-air interactions at ultra-high energies in muon-depleted air showers with different depths

The hardness of the energy spectrum of neutral pions produced in proton-air interactions at ultra-high energies, above $10^{18}$ eV, is constrained by the steepness of the shower-to-shower distribution of the number of muons in muon-depleted extensive air showers. In this work, we find that this steepness, quantified by the parameter $Λ_μ$, evolves with the depth of the shower maximum, $X_{\max}$, assuming a universal value for shallow showers and an enhanced dependence on the high-energy hadronic interaction model for deep showers. We show that Xmax probes the so-called hadronic activity of the first interaction, thus allowing direct access to the energy spectrum of neutral pions in different regions of the kinematic phase space of the first interaction. We verify that the unbiased measurement of $Λ_μ$ is possible for realistic mass composition expectations. Finally, we infer that the statistical precision in $Λ_μ$ required to distinguish between hadronic interaction models can be achieved in current extensive air shower detectors, given their resolution and exposure.

astro-ph.HE↗

arXiv2024

Sibyll$^{\bigstar}$

In the last decade, an increasing number of datasets have revealed a consistent discrepancy between the number of muons measured in ultra-high-energy extensive air showers (EAS) and the numbers predicted by simulations. This gap persists despite incorporating Large Hadron Collider (LHC) data into the tuning of current hadronic interaction models, leading to the phenomenon often termed the ''muon puzzle''. To gain a deeper understanding of the potential origins of this muon puzzle, we have developed Sibyll$^{\bigstar}$, a series of phenomenologically modified versions of Sibyll 2.3d. In these models, we have increased muon production by altering $ρ^0$, baryon-antibaryon pair, or kaon production in hadronic multiparticle production processes. These variants remain within bounds from provided by accelerator measurements, including those from the LHC and fixed-target experiments, notably NA49 and NA61, showing a level of consistency comparable to Sibyll 2.3d. Our findings show that these modifications can increase the muon count in EAS by up to 35%, while minimally affecting the depth of shower maximum ($X_{\rm max}$) and other shower variables. Additionally, we assess the impact of these modifications on various observables, including inclusive muon and neutrino fluxes and the multiplicities of muon bundles in deep underground and water/ice Cherenkov detectors. We aim for at least one of these model variants to offer a more accurate representation of EAS data at the highest energies, thereby enhancing the quality of Monte Carlo predictions used in training neural networks. This improvement is crucial for achieving more reliable data analyses and interpretations.

hep-ph↗

arXiv2023

Sibyll$^\bigstar$: ad-hoc modifications for an improved description of muon data in extensive air showers

Current simulations of air showers produced by ultra-high energy cosmic rays (UHECRs) do not satisfactorily describe recent experimental data, particularly when looking at the muonic shower component relative to the electromagnetic one. Discrepancies can be seen in both average values and on an individual shower-by-shower basis. It is thought that the muonic part of the air showers isn't accurately represented in simulations, despite various attempts to boost the number of muons within standard hadronic interaction physics. In this study, we investigate whether modifying the final state of events created with Sibyll~2.3d in air shower simulations can achieve a more consistent description of the muon content observed in experimental data. We create several scenarios where we separately increase the production of baryons, $ρ^0$, and strange particles to examine their impact on realistic air shower simulations. Our results suggest that these ad-hoc modifications can improve the simulations, providing a closer match to the observed muon content in air showers. One side-effect of the increased muon production in the considered model versions is a smaller difference in the predicted total muon numbers for proton and iron showers. However, more research is needed to find out whether any of these adjustments offers a realistic solution to the mismatches seen in data, and to identify the precise physical process causing these changes in the model. We hope that these modified model versions will also help to develop improved machine-learning analyses of air shower data and to estimate sys.{} uncertainties related to shortcomings of hadronic interaction models.

astro-ph.HE↗

arXiv2023

Validation of Electromagnetic Showers in CORSIKA 8

The air shower simulation code CORSIKA has served as a key part of the simulation chain for numerous astroparticle physics experiments over the past decades. Due to retirement of the original developers and the increasingly difficult maintenance of the monolithic Fortran code of CORSIKA, a new air shower simulation framework has been developed over the course of the last years in C++, called CORSIKA 8. Besides the hadronic and muonic component, the electromagnetic component is one of the key constituents of an air shower. The cascade producing the electromagnetic component of an air shower is driven by bremsstrahlung and photoproduction of electron-positron pairs. At ultrahigh energies or in media with high densities, the bremsstrahlung and pair production processes are suppressed by the Landau-Pomeranchuk-Migdal (LPM) effect, which leads to more elongated showers compared to showers without the LPM suppression. Furthermore, photons at higher energies can produce muon pairs or interact hadronically with nucleons in the target medium, producing a muon component in electromagnetic air showers. In this contribution, we compare electromagnetic showers simulated with the latest Fortran version of CORSIKA and CORSIKA 8, which uses the library PROPOSAL for the electromagnetic component. While earlier validations of CORSIKA 8 electromagnetic showers focused on showers of lower energy, the recent implementation of the LPM effect, photo pair production of muons, and of photohadronic interactions allows now to make a physics-complete comparison also at high energies.

astro-ph.HE↗

arXiv2023

Universality of the muon component of extensive air showers

In extensive air shower experiments, the number of muons crossing a detector at a given position, as well as their arrival time, arrival direction, and energy, are determined by a more fundamental 3-dimensional distribution linked to the hadronic core of the shower. Muons are produced high up in the atmosphere after the decay of mesons in the hadronic cascade. The distributions of production depth, energy, and transverse momentum of muons are enough to fully predict the muon component of air showers in any particular observational condition. By using air-shower simulations with the state-of-the-art hadronic interaction models, the mentioned distributions at production are analyzed as a function of zenith angle, primary mass, and hadronic interaction model, and their level of universality is studied and assessed in an exhaustive manner for the first time.

hep-ph↗

arXiv2021

CORSIKA 8 -- Contributions to the 37th International Cosmic Ray Conference in Berlin Germany (ICRC 2021)

Compilation of the six contributions to the ICRC conference 2021 by the CORSIKA 8 Collaboration. The status of the project is illustrated. In particular, the secondary hadron as well as the electromagnetic cascades are being validated individually, and current results are reviewed. A novel framework for radio emission simulations is presented, which is designed given the modular nature of CORSIKA 8 to support, both, the CoREAS as well as the ZHS formalism. At the same time, first Cherenkov emission calculations are shown which are based on CORSIKA 8 coupled with a GPU Cherenkov emission code. Finally, a new powerful feature of CORSIKA 8 is illustrated, where the entire genealogy of air shower particles can be studied in all details.

astro-ph.HE↗

arXiv2021

Constraining the energy spectrum of neutral pions in ultra-high-energy proton-air interactions

Fluctuations in the muon content of extensive air showers are anticorrelated to the fluctuations of the energy taken by the neutral pions which emerge from the first interaction of the cosmic ray in the atmosphere. We show that the high-energy tail of the neutral pion spectrum produced in the first proton-air interaction can be constrained, within the uncertainties of present cosmic ray experiments, through the analysis of the shower-to-shower distribution of the muon content of the air showers, $P(N_μ)$.

astro-ph.HE↗

arXiv2020

Hadronic interaction model Sibyll 2.3d and extensive air showers

We present a new version of the hadron interaction event generator Sibyll. While the core ideas of the model have been preserved, the new version handles the production of baryon pairs and leading particles in a new way. In addition, production of charmed hadrons is included. Updates to the model are informed by high-precision measurements of the total and inelastic cross sections with the forward detectors at the LHC that constrain the extrapolation to ultra-high energy. Minimum-bias measurements of particle spectra and multiplicities support the tuning of fragmentation parameters. This paper demonstrates the impact of these changes on air shower observables such as $X_{\rm max}$ and $N_μ$, drawing comparisons with other contemporary cosmic ray interaction models.

hep-ph↗

arXiv2020

Self-consistent approach for measuring the energy spectra and composition of cosmic rays and determining the properties of hadronic interactions at high energy

Air showers, produced by the interaction of energetic cosmic rays with the atmosphere, are an excellent alternative to study particle physics at energies beyond any human-made particle accelerator. For that, it is necessary to identify first the mass composition of the primary cosmic ray (and its energy). None of the existing high energy interaction models have been able to reproduce coherently all air shower observables over the entire energy and zenith angle phase space. This is despite having tried all possible combinations for the cosmic ray mass composition. This proposal outlines a self-consistent strategy to study high energy particle interactions and identify the energy spectra and mass composition of cosmic rays. This strategy involves the participation of different particle accelerators and astrophysics experiments. This is important to cover the entire cosmic ray energy range and a larger phase-space of shower observables to probe the high energy interaction models.

astro-ph.HE↗