arXiv subjects

Markus Risse

Publications and source records attributed to Markus Risse.

14 recordsLinked to original sources

arXiv2026

Cosmogenic photon fluxes at ultra-high energies

During their propagation, ultra-high energy cosmic rays produce cosmogenic photons. The expected flux level of these photons may vary by orders of magnitude depending on parameters such as the spectrum and composition of cosmic rays at injection or the source distance. We investigate the photon yields for various assumptions on injection parameters. The photon yield is largest for proton-emitting sources at about 15 Mpc distance for cosmogenic photons above $10^{18}$ eV. While the photon yield from protons always exceeds the one from heavier nuclei of the same total energy, the differences are reduced for larger source distances. Then, we quantify the cosmogenic photon fluxes for different source scenarios. We regard mixed-composition scenarios that were found to provide a reasonable description of the data from the Pierre Auger Observatory. In addition, benchmark scenarios leading to comparably high ("maximum") or low ("minimum") photon fluxes are determined assuming pure proton or pure iron primaries. For the mixed-composition scenarios that do not contain initial protons, the predicted cosmogenic photon fluxes are below present experimental limits by more than 1.5 orders of magnitude. In case of a substantial fraction of protons at the highest energies, the related photon flux might be in reach. Certain parameter combinations of pure proton scenarios are constrained already by present photon limits.

astro-ph.HE↗

arXiv2025

Subatomic Heroes

Sharing the amazing achievements of the (particle) physics world with the general public is at the heart of the mission of the Subatomic Heroes, based at the University of Siegen, Germany. Originally this started out as an endeavor of theoretical particle physics, now we are steadily spreading out to cover and include more branches of physics and science. Our activities range from merging art with public physics lectures via marvelous artistic performances at the local theater, over dedicated events for high-school students, to our Subatomic Heroes channel on Instagram and TikTok where you may also find out when and where our famous "hadronic ice-cream" will be served next! So follow us on https://www.instagram.com/subatomic_heroes and https://www.tiktok.com/@subatomic_heroes.

physics.ed-ph↗

arXiv2024

Towards Searching for Photons with Energies beyond the PeV Range from Galactic PeVatrons

Several gamma-ray observatories have discovered photons of cosmic origin with energies in the PeV ($10^{15}\,\text{eV}$) range. Photons at these energies might be produced as by-products from particle acceleration in so-called PeVatrons, which are widely assumed to be the sources of a large part of galactic cosmic rays. Based on recent measurements of these PeV $\gamma$-sources by LHAASO and HAWC, we extrapolate the energy spectra of selected sources up to the ultra-high-energy (UHE, ${\geq}10\,\text{PeV}$) regime. The goal of this study is to evaluate if (and under what conditions) giant air-shower observatories, for example the Pierre Auger Observatory, could contribute to testing the UHE luminosity of PeV $\gamma$-sources. Possible propagation effects are investigated as well as the required discrimination power to distinguish photon- and hadron-initiated air showers. For present detector setups, it turns out to be challenging to achieve the required sensitivity due to the energy threshold being too high or the detection area too small. Dedicated detector concepts appear to be needed to explore the UHE frontier. Ultimately, this could provide complementary information on the sources of cosmic rays beyond the PeV regime -- a key objective of current efforts in multimessenger astronomy.

astro-ph.HE↗

arXiv2023

A new bound on Lorentz violation based on the absence of vacuum Cherenkov radiation in ultra-high energy air showers

In extensive air showers induced by ultra-high energy (UHE) cosmic rays, secondary particles are produced with energies far above those accessible by other means. These extreme energies can be used to search for new physics. We study the effects of isotropic, nonbirefringent Lorentz violation in the photon sector. In case of a photon velocity smaller than the maximum attainable velocity of standard Dirac fermions, vacuum Cherenkov radiation becomes possible. Implementing this Lorentz-violating effect in air shower simulations, a significant reduction of the calculated average atmospheric depth of the shower maximum $\left $ is obtained. Based on $\left $ and its shower-to-shower fluctuations $σ(X_\text{max})$, a new bound on Lorentz violation is derived which improves the previous one by a factor of 2. This is the first such bound based on the absence of vacuum Cherenkov radiation from fundamental particles (electrons and positrons) in air showers. Options for further improvements are discussed.

hep-ph↗

arXiv2022

Using ultra-high energy cosmic rays and air showers to test Lorentz invariance within modified Maxwell theory

Cosmic rays and air showers at ultra-high energy are unique tools to test the validity of Lorentz invariance. A brief overview is given on such tests focusing on isotropic, non-birefringent Lorentz violation (LV) in the photon sector. Based on the apparent absence of vacuum Cherenkov radiation and photon decay, the LV parameter $κ$ is bound to $-0.6 \cdot 10^{-20} < κ< 6 \cdot 10^{-20}$ (98\% CL). We report an updated limit from cosmic-ray photon observations and preliminary results on testing vacuum Cherenkov radiation in air showers.

hep-ph↗

arXiv2021

Photon decay in UHE air showers: stringent bound on Lorentz violation

In extensive air showers induced by ultra-high-energy (UHE) cosmic rays, secondary photons are expected to be produced at energies far above those accessible by other means. It has been shown that the decay of such photons, as possible in certain theories allowing Lorentz violation, can lead to significant changes of the shower development. Based on observations of the average depth of the shower maximum $\left $, a stringent bound on Lorentz violation has been placed in a previous work. Here we include the shower-to-shower fluctuations $σ(X_\text{max})$ as an additional observable. The combined comparison of $\left $ and $σ(X_\text{max})$ to shower observations allows a much stricter test of the possible decay of UHE photons, improving the previous bound by a factor of 50.

hep-ph↗

arXiv2016

Determination of the proton-to-helium ratio in cosmic rays at ultra-high energies from the tail of the $X_{\rm max}$ distribution

We present a method to determine the proton-to-helium ratio in cosmic rays at ultra-high energies. It makes use of the exponential slope, $Λ$, of the tail of the $X_{\rm max}$ distribution measured by an air shower experiment. The method is quite robust with respect to uncertainties from modeling hadronic interactions and to systematic errors on $X_{\rm max}$ and energy, and to the possible presence of primary nuclei heavier than helium. Obtaining the proton-to-helium ratio with air shower experiments would be a remarkable achievement. To quantify the applicability of a particular mass-sensitive variable for mass composition analysis despite hadronic uncertainties we introduce as a metric the `analysis indicator' and find an improved performance of the $Λ$ method compared to other variables currently used in the literature. The fraction of events in the tail of the $X_{\rm max}$ distribution can provide additional information on the presence of nuclei heavier than helium in the primary beam.

astro-ph.HE↗

arXiv2014

A method to calibrate the absolute energy scale of air showers with ultra-high energy photons

Calibrating the absolute energy scale of air showers initiated by ultra-high energy cosmic rays is an important experimental issue. Currently, the corresponding systematic uncertainty amounts to 14-21% using the fluorescence technique. Here we describe a new, independent method which can be applied if ultra-high energy photons are observed. While such photon-initiated showers have not yet been identified, the capabilities of present and future cosmic-ray detectors may allow their discovery. The method makes use of the geomagnetic conversion of UHE photons (preshower effect), which significantly affects the subsequent longitudinal shower development. The conversion probability depends on photon energy and can be calculated accurately by QED. The comparison of the observed fraction of converted photon events to the expected one allows the determination of the absolute energy scale of the observed photon air showers and, thus, an energy calibration of the air shower experiment. We provide details of the method and estimate the accuracy that can be reached as a function of the number of observed photon showers. Already a very small number of UHE photons may help to test and fix the absolute energy scale.

astro-ph.IM↗

arXiv2012

Sensitivity of the correlation between the depth of shower maximum and the muon shower size to the cosmic ray composition

The composition of ultra-high energy cosmic rays is an important issue in astroparticle physics research, and additional experimental results are required for further progress. Here we investigate what can be learned from the statistical correlation factor r between the depth of shower maximum and the muon shower size, when these observables are measured simultaneously for a set of air showers. The correlation factor r contains the lowest-order moment of a two-dimensional distribution taking both observables into account, and it is independent of systematic uncertainties of the absolute scales of the two observables. We find that, assuming realistic measurement uncertainties, the value of r can provide a measure of the spread of masses in the primary beam. Particularly, one can differentiate between a well-mixed composition (i.e., a beam that contains large fractions of both light and heavy primaries) and a relatively pure composition (i.e., a beam that contains species all of a similar mass). The number of events required for a statistically significant differentiation is ~ 200. This differentiation, though diluted, is maintained to a significant extent in the presence of uncertainties in the phenomenology of high energy hadronic interactions. Testing whether the beam is pure or well-mixed is well motivated by recent measurements of the depth of shower maximum.

astro-ph.HE↗

arXiv2009

Simulation study of GZK photon fluxes

The composition of ultra-high energy (UHE) cosmic rays E>10^17 eV is still unknown. The observation of UHE photons would extend the observed electromagnetic spectrum to highest energy and open a new channel for multimessenger observations in the universe. Current limits on the photon flux already constrain ``exotic'' scenarios where a large number of photons is expected by the decay products of supermassive X-particles. Motivated by the growing exposure of UHE cosmic ray experiments - like the Pierre Auger Observatory - the observation of conventionally produced GZK photons may be in reach in the near future. We investigate UHE particle propagation using the Monte Carlo code CRPropa. Particularly, the expected photon fluxes normalized to current experiments as well as prospects for future experiments are illustrated. Varying source and propagation scenarios are analyzed and the impact on secondary GZK photons is shown. For the specific case of Centaurus A, we study which source parameters can be tested by searching for the expected GZK photons.

astro-ph.HE↗

arXiv2007

Search for ultra-high energy photons using air showers

The observation of photons with energies above 10^18 eV would open a new window in cosmic-ray research, with possible impact on astrophysics, particle physics, cosmology and fundamental physics. Current and planned air shower experiments, particularly the Pierre Auger Observatory, offer an unprecedented opportunity to search for such photons and to complement efforts of multimessenger observations of the universe. We summarize motivation, achievements, and prospects of the search for ultra-high energy photons.

astro-ph↗

arXiv2007

An upper limit to photons from first data taken by the Pierre Auger Observatory

Many models for ultra-high energy cosmic rays postulate exotic scenarios to explain the sources or the nature of these particles. A characteristic feature of these models is the prediction of a significant flux of photons at ultra-high energy. The Pierre Auger Observatory offers a great potential to search for such photons. We present shower observables with sensitivity to photons and the search strategy employed. An upper limit to photon primaries is derived from first Auger data. Prospects for constraining theoretical source models are discussed.

astro-ph↗

arXiv2004

Properties of Extensive Air Showers

Some general properties of extensive air showers are discussed. The main focus is put on the longitudinal development, in particular the energy flow, and on the lateral distribution of different air shower components. The intention of the paper is to provide a basic introduction to the subject rather than a comprehensive review.

astro-ph↗

arXiv2003

Energy Release in Air Showers

A simulation study of the energy released in air due to the development of an extensive air shower has been carried out using the CORSIKA code. The contributions to the energy release from different particle species and energies as well as the typical particle densities are investigated. Special care is taken of particles falling below the energy threshold of the simulation which contribute about 10% to the total energy deposition. The dominant contribution to the total deposition stems from electrons and positrons from sub-MeV up to a few hundred MeV, with typical transverse distances between particles exceeding 1 mm for 10 EeV showers.

astro-ph↗