In cosmic ray physics and high-energy neutrino astronomy, muons are ubiquitous. Due to their slow energy loss and consequently large range at high energies, the correct simulation of their transport ...through matter is especially important for underground experiments. The dominant energy loss processes are ionization and at higher energies pair production, bremsstrahlung and inelastic interaction with nuclei. A muon energy loss process, which has hitherto been neglected in such simulations, is the diffractive scattering of virtual photons on nuclei. As the elastic channel of this process has the same final state as the bremsstrahlung process
(
μ
+
A
→
μ
+
A
+
γ
)
, an interference term arises, whose sign depends on the charge of the lepton. It is found that the contribution of this process was overestimated in earlier works and is significantly affected by shadowing.
Abstract We reexamine the interactions of ultra-high-energy cosmic rays (UHECRs) with photons from the cosmic microwave background (CMB) under a changed, locally nonlinear temperature–redshift ...relation T ( z ). This changed temperature–redshift relation has recently been suggested by the postulate of subjecting thermalized and isotropic photon gases such as the CMB to an SU(2) rather than a U(1) gauge group. This modification of ΛCDM is called SU(2) CMB , and some cosmological parameters obtained by SU(2) CMB seem to be in better agreement with local measurements of the same quantities, in particular H 0 and S 8 . In this work, we apply the reduced CMB photon density under SU(2) CMB to the propagation of UHECRs. This leads to a higher UHECR flux just below the ankle in the cosmic ray spectrum and slightly more cosmogenic neutrinos under otherwise equal conditions for emission and propagation. Most prominently, the proton flux is significantly increased below the ankle (5 × 10 18 eV) for hard injection spectra and without considering the effects of magnetic fields. The reduction in CMB photon density also favors a decreased cosmic ray source evolution than the best fit using ΛCDM. In consequence, it seems that SU(2) CMB favors sources that evolve like the star formation rate, such as starburst galaxies and gamma-ray bursts, over active galactic nuclei as origins of UHECRs. We conclude that the question about the nature of primary sources of UHECRs is directly affected by the assumed temperature–redshift relation of the CMB.
Large scale neutrino detectors and muography rely on the muon direction in the detector to infer the muon’s or parent neutrino’s origin. However, muons accumulate deflections along their propagation ...path prior to entering the detector, which may need to be accounted for as an additional source of uncertainty. In this paper, the deflection of muons is studied with the simulation tool PROPOSAL, which accounts for multiple scattering and deflection on stochastic interactions. Deflections along individual interactions depend on the muon energy and the interaction type, and can reach up to the order of degrees – even at TeV to PeV energies. The accumulated deflection angle can be parametrized in dependence of the final muon energy, independent of the initial muon energy. The median accumulated deflection of a propagated muon with a final energy of
500
GeV
is
θ
acc
=
0.10
∘
with a
99
%
central interval of
0.01
∘
,
0.39
∘
. This is on the order of magnitude of the directional resolution of present neutrino detectors. Furthermore, comparisons with the simulation tools MUSIC and
Geant4
as well as two different muon deflection measurements are performed.
The lepton propagator PROPOSAL is a Monte-Carlo Simulation library written in C++, propagating high energy muons and other charged particles over large distances in media. In this article, a ...restructuring of the code is described, which yields a performance improvement of up to 30%. For an improved accuracy of the propagation processes, more exact calculations of the leptonic and hadronic decay process and more precise parametrizations for the interaction cross sections are now available. The new modular structure allows a more flexible and customized usage, which is further facilitated with a Python interface.
Program Title: PROPOSAL
Program Files doi:http://dx.doi.org/10.17632/g478pjdcxy.1
Licensing provisions: LGPL
Programming language: C++
Nature of problem: Propagation of charged particles over large distances in three dimensions through different kinds of media. These particles lose their energy stochastically via the processes of ionization, pair production, bremsstrahlung and inelastic nuclear interaction and eventually decay, producing secondary particles along the trajectory.
Solution method: Monte-Carlo simulation. The program samples the next stochastic interaction point, the type of interaction and the amount of energy lost in the interaction until either the particle decays, its energy is below a certain threshold or it reaches a given distance. To improve the performance and to deal with the bremsstrahlung divergence at small energy losses, an adaptable energy cut is used below which all losses are treated continuously. The use of interpolation tables further reduces computation time.
The sampled energy till the next stochastic loss is smeared out with a Gaussian randomization inside the physically allowed limits of the continuous losses using the second moment of the summed processes to avoid artifacts introduced by the energy cut. The deviation from a straight trajectory is evaluated using the multiple scattering calculation by Molière or the Highland parametrization, a Gaussian approximation to Molière’s theory. Multiple kinds of parametrizations are also available for bremsstrahlung, pair production and inelastic nuclear interaction to study the effects of the uncertainty of the cross sections on the propagation and further simulation steps.
ABSTRACT
The FR-I galaxy 3C 84, that is identified with the misaligned blazar NGC 1275, is well known as one of the very few radio galaxies emitting gamma-rays in the TeV range. Yet, the gamma-ray ...emission region cannot be pinpointed and the responsible mechanisms are still unclear. We calculate the optical absorption depth of high-energy photons in the broad-line region of 3C 84 depending on their energy and distance to the central black hole. Based on these calculations, a lower limit on the distance of the emission region from the central black hole can be derived. These lower limits are estimated for two broad-line region geometries (shell and ring) and two states of the source, the low state in 2016 October–December and a flare state in 2017 January. For the shell geometry, we can place the emission region outside the Ly α radius. For the ring geometry and the low flux activity, the minimal distance between the black hole, and the gamma-ray emission region is close to the Ly α radius. In the case of the flaring state (ring geometry), the results are not conclusive. Our results exclude the region near the central black hole as the origin of the gamma-rays detected by Fermi–LAT and Major Atmospheric Gamma-Ray Imaging Cherenkov. With these findings, we can constrain the theoretical models of acceleration mechanisms and compare the possible emission region to the source’s morphology resolved by radio images from the Very Long Baseline Array.
Accurate particle simulations are essential for the next generation of experiments in astroparticle physics. The Monte Carlo simulation library PROPOSAL is a flexible tool to efficiently propagate ...high-energy leptons and photons through large volumes of media, for example in the context of underground observatories. It is written as a C++ library, including a Python interface. In this paper, the most recent updates of PROPOSAL are described, including the addition of electron, positron, and photon propagation, for which new interaction types have been implemented. This allows the usage of PROPOSAL to simulate electromagnetic particle cascades, for example in the context of air shower simulations. The precision of the propagation has been improved by including rare interaction processes, new photonuclear parametrizations, deflections in stochastic interactions, and the possibility of propagating in inhomogeneous density distributions. Additional technical improvements regarding the interpolation routine and the propagation algorithm are described.
Program Title: PROPOSAL.
CPC Library link to program files:https://doi.org/10.17632/g478pjdcxy.2.
Developer's repository link:https://github.com/tudo-astroparticlephysics/PROPOSAL.
Licensing provisions: LGPL.
Programming language: C++, Python.
Journal reference of previous version: Comput. Phys. Commun. 242 (2019) 132.
Does the new version supersede the previous version?: Yes.
Reasons for the new version: Substantial addition of features. Various bugfixes.
Summary of revisions: The library now also treats photons and has the corresponding processes implemented. New parametrizations for photonuclear interaction have been implemented. The angular deflection in stochastic energy losses has been implemented in addition to the already existing multiple scattering implementation, which has been improved to reduce the runtime. The implementation of the Landau-Pomeranchuk-Migdal effect has been corrected. The propagation algorithm has been improved, including the support of inhomogeneous density distributions.
Nature of problem: Three-dimensional propagation of charged leptons and photons through different media. Particles lose energy stochastically by ionization, bremsstrahlung, pair production, and photonuclear interaction for charged leptons (including annihilation with atomic electrons for positrons) and Compton scattering, pair production, photoelectric effect and photohadronic interaction for photons. Additionally, they are deflected while propagating through the medium due to both multiple elastic Coulomb scattering as well as deflections in individual stochastic interactions. Unstable particles eventually decay, producing secondary particles.
Solution method: Monte-Carlo simulation. The library samples the next interaction point, the type of interaction process, the energy lost in this interaction process, and the energy lost until this point. Particles are propagated until they decay, lose all their kinetic energy (for photons: reach a lower energy limit defined by the validity of the underlying cross sections), or until a user-defined termination criterion is reached. For each propagation step, the angular deflection and endpoint shift due to multiple scattering is calculated.
To improve the performance and deal with the divergence of the bremsstrahlung cross section for small photon energies, energy losses below a predefined relative or absolute energy threshold are treated continuously. The computation time is improved by the use of interpolation tables.
Relic neutrinos from the early universe are predicted to have a relatively
large number density, but extremely low energies. Hence, the only possible
interaction proceeds via neutrino capture on ...beta-decaying nuclei. In case
relic neutrinos are captured by beta-decaying nuclei in the Sun, the neutrinos
normally emerging from the decay of these nuclei will be missing from the
overall number of solar neutrinos registered in neutrino experiments. Within
the Sun, ^8\mathrm{B}$ and three nuclei from the CNO cycle are found to be
suitable for this kind of process. Their cross section as well as the possible
impact on the observed number of solar neutrinos are discussed. Assuming
standard neutrino oscillations, no deviations of neutrino flux measurements
from the predictions of the solar standard model are observed and upper limits
are derived accordingly.
The Fortran-versions of the CORSIKA air shower simulation code have been at the core of simulations for many astroparticle physics experiments for the last 30 years. Having grown over decades into an ...ever more complex software, maintainability of CORSIKA has become increasingly difficult, though its performance is still excellent. In 2018, therefore a complete rewrite of CORSIKA has begun in modern modular C++. Today, CORSIKA 8 has reached important milestones with a full-fledged implementation of both the hadronic and electromagnetic cascades, the ability to simulate radio and Cherenkov-light emission from air showers and an unprecedented flexibility to configure simulation media and their geometries. This presentation will discuss the current status of CORSIKA 8, highlight the new possibilities already available, and future prospects of this new air shower simulation framework.
The energy reconstruction of high-energy muons depends on the energy loss characteristics. Accurate knowledge of the cross sections of the energy loss processes is necessary for precise measurements ...of the energy spectrum of muons and muon-induced neutrinos. The cross sections of the two most dominant processes, electron pair production and bremsstrahlung are calculated exact in the coupling parameter \(Z\alpha\) to the electromagnetic field of a nucleus for realistic extended screened nuclei. An analytical parametrization of the mass and nuclear-charge dependence of the cross section is given.
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