Browsing by Author "Riehn, Felix"
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- A state-of-the-art calculation of atmospheric lepton fluxesPublication . Fedynitch, Anatoli; Dembinski, Hans; Engel, Ralph; Gaisser, Thomas K.; Riehn, Felix; Stanev, TodorAtmospheric leptons are of continuous interest for several scientific communities. At low and intermediate energies, atmospheric neutrinos are the signal for studies of fundamental neutrino properties and at high energies, they constitute the background for the characterization of the features of the astrophysical neutrino flux. We have studied in depth the relation between observable inclusive lepton fluxes/ratios and hadronic interactions by using a novel numerical transport equation solver MCEq. It enables us to characterize, with an unprecedented precision, relevant particle interaction energies, important hadron species, and the secondary particle production phase-space in terms of typical accelerator observables. Based on our findings, we improved existing interaction models S IBYLL and D PMJET and created an efficient scheme to propagate correlated model uncertainties into derived lepton fluxes. We present state-of-the-art calculations of inclusive lepton fluxes and discuss possible directions towards reducing uncertainties below 10%.
- An Indication of anisotropy in arrival directions of ultra-high-energy cosmic rays through comparison to the flux pattern of extragalactic gamma-ray sourcesPublication . Pierre Auger collaboration (392 authors); Abreu, Pedro; Andringa, Sofia; Assis, Pedro; Barreira Luz, Ricardo Jorge; Blanco, Alberto; Cazon, Lorenzo; Conceição, Ruben; Diogo, Francisco; Espadanal, João; Lopes, Luis; Pimenta, Mário; Riehn, Felix; Santos, Eva; Sarmento, Raul; Tomé, BernardoA new analysis of the data set from the Pierre Auger Observatory provides evidence for anisotropy in the arrival directions of ultra-high-energy cosmic rays on an intermediate angular scale, which is indicative of excess arrivals from strong, nearby sources. The data consist of 5514 events above with zenith angles up to 80° recorded before 2017 April 30. Sky models have been created for two distinct populations of extragalactic gamma-ray emitters: active galactic nuclei from the second catalog of hard Fermi-LAT sources (2FHL) and starburst galaxies from a sample that was examined with Fermi-LAT. Flux-limited samples, which include all types of galaxies from the Swift-BAT and 2MASS surveys, have been investigated for comparison. The sky model of cosmic-ray density constructed using each catalog has two free parameters, the fraction of events correlating with astrophysical objects, and an angular scale characterizing the clustering of cosmic rays around extragalactic sources. A maximum-likelihood ratio test is used to evaluate the best values of these parameters and to quantify the strength of each model by contrast with isotropy. It is found that the starburst model fits the data better than the hypothesis of isotropy with a statistical significance of 4.0σ, the highest value of the test statistic being for energies above . The three alternative models are favored against isotropy with 2.7σ–3.2σ significance. The origin of the indicated deviation from isotropy is examined and prospects for more sensitive future studies are discussed.
- Data-driven model of the cosmic-ray flux and mass composition from 10 GeV to $10^{11}$ GeVPublication . Dembinski, Hans Peter; Engel, Ralph; Fedynitch, Anatoli; Gaisser, Thomas; Riehn, Felix; Stanev, TodorWe present a new parametrization of the cosmic-ray flux and its mass composition over an energy range from 10 GeV to $10^{11}$ GeV. Our approach is data-driven and relies on theoretical assumptions as little as possible. We combine measurements of the flux of individual elements from high-precision satellites and balloon experiments with indirect measurements of mass groups from the leading air shower experiments. To our knowledge, we provide the first fit of this kind that consistently takes both statistical and systematic uncertainties into account. The uncertainty on the energy scales of individual experiments is handled explicitly in our mathematical approach. Part of our results is a common energy scale and adjustment factors for the energy scales of the participating experiments. Our fit has a reduced $\chi^2$-value of 0.5, showing that experimental data are in good agreement, if systematic uncertainties are considered. Our model may serve as a world-average of the measured fluxes for individual elements from proton to iron from 10 GeV to $10^{11}$ GeV. It is useful as an input for simulations or theoretical computations based on cosmic rays. The experimental uncertainties of the input data are captured in a covariance matrix, which can be propagated into derived quantities.
- Inferences on mass composition and tests of hadronic interactions from 0.3 to 100 EeV using the water-Cherenkov detectors of the Pierre Auger ObservatoryPublication . Pierre Auger collaboration (405 authors); Abreu, Pedro; Andringa, Sofia; Assis, Pedro; Barreira Luz, Ricardo Jorge; Blanco, Alberto; Cazon, Lorenzo; Conceição, Ruben; Diogo, Francisco; Espadanal, João; Lopes, Luis; Pimenta, Mário; Riehn, Felix; Santos, Eva; Sarmento, Raul; Tomé, BernardoWe present a new method for probing the hadronic interaction models at ultra-high energy and extracting details about mass composition. This is done using the time profiles of the signals recorded with the water-Cherenkov detectors of the Pierre Auger Observatory. The profiles arise from a mix of the muon and electromagnetic components of air-showers. Using the risetimes of the recorded signals we define a new parameter, which we use to compare our observations with predictions from simulations. We find, firstly, inconsistencies between our data and predictions over a greater energy range and with substantially more events than in previous studies. Secondly, by calibrating the new parameter with fluorescence measurements from observations made at the Auger Observatory, we can infer the depth of shower maximum for a sample of over 81,000 events extending from 0.3 EeV to over 100 EeV. Above 30 EeV, the sample is nearly fourteen times larger than currently available from fluorescence measurements and extending the covered energy range by half a decade. The energy dependence of the average depth of shower maximum is compared to simulations and interpreted in terms of the mean of the logarithmic mass. We find good agreement with previous work and extend the measurement of the mean depth of shower maximum to greater energies than before, reducing significantly the statistical uncertainty associated with the inferences about mass composition.
- Large-scale cosmic-ray anisotropies above 4 EeV measured by the Pierre Auger ObservatoryPublication . Pierre Auger collaboration (376 authors); Abreu, Pedro; Andringa, Sofia; Assis, Pedro; Barreira Luz, Ricardo Jorge; Blanco, Alberto; Cazon, Lorenzo; Conceição, Ruben; Diogo, Francisco; Lopes, Luis; Pimenta, Mário; Riehn, Felix; Santos, Eva; Sarmento, Raul; Tomé, BernardoWe present a detailed study of the large-scale anisotropies of cosmic rays with energies above 4 EeV measured using the Pierre Auger Observatory. For the energy bins [4,8] EeV and $E\geq 8$ EeV, the most significant signal is a dipolar modulation in right ascension at energies above 8 EeV, as previously reported. In this paper we further scrutinize the highest-energy bin by splitting it into three energy ranges. We find that the amplitude of the dipole increases with energy above 4 EeV. The growth can be fitted with a power law with index $\beta=0.79\pm 0.19$. The directions of the dipoles are consistent with an extragalactic origin of these anisotropies at all the energies considered. Additionally we have estimated the quadrupolar components of the anisotropy: they are not statistically significant. We discuss the results in the context of the predictions from different models for the distribution of ultrahigh-energy sources and cosmic magnetic fields.
- Observation of inclined EeV air showers with the radio detector of the Pierre Auger ObservatoryPublication . Pierre Auger collaboration (394 authors); Abreu, Pedro; Andringa, Sofia; Assis, Pedro; Barreira Luz, Ricardo Jorge; Blanco, Alberto; Cazon, Lorenzo; Conceição, Ruben; Diogo, Francisco; Lopes, Luis; Pimenta, Mário; Riehn, Felix; Santos, Eva; Sarmento, Raul; Tomé, BernardoWith the Auger Engineering Radio Array (AERA) of the Pierre Auger Observatory, we have observed the radio emission from 561 extensive air showers with zenith angles between 60o and 84o. In contrast to air showers with more vertical incidence, these inclined air showers illuminate large ground areas of several km2 with radio signals detectable in the 30 to 80 MHz band. A comparison of the measured radio-signal amplitudes with Monte Carlo simulations of a subset of 50 events for which we reconstruct the energy using the Auger surface detector shows agreement within the uncertainties of the current analysis. As expected for forward-beamed radio emission undergoing no significant absorption or scattering in the atmosphere, the area illuminated by radio signals grows with the zenith angle of the air shower. Inclined air showers with EeV energies are thus measurable with sparse radio-antenna arrays with grid sizes of a km or more. This is particularly attractive as radio detection provides direct access to the energy in the electromagnetic cascade of an air shower, which in case of inclined air showers is not accessible by arrays of particle detectors on the ground.
- Probing the energy spectrum of hadrons in proton air interactions at ultrahigh energies through the fluctuations of the muon content of extensive air showersPublication . Cazon, Lorenzo; Conceição, Ruben; Riehn, FelixWe demonstrate that the shower-to-shower fluctuations of the muon content of extensive air showers correlate with the fluctuations of a variable of the first interaction of Ultra High Energy Cosmic Rays, which is computed from the fraction of energy carried by the hadrons that sustain the hadronic cascade. The influence of subsequent stages of the shower development is found to play a sub-dominant role. As a consequence, the shower-to-shower distribution of the muon content is a direct probe of the hadron energy spectrum of interactions beyond 100 TeV center of mass energies.
- Spectral Calibration of the Fluorescence Telescopes of the Pierre Auger ObservatoryPublication . Pierre Auger collaboration (404 authors); Abreu, Pedro; Andringa, Sofia; Assis, Pedro; Barreira Luz, Ricardo Jorge; Blanco, Alberto; Cazon, Lorenzo; Conceição, Ruben; Diogo, Francisco; Espadanal, João; Lopes, Luis; Pimenta, Mário; Riehn, Felix; Santos, Eva; Sarmento, Raul; Tomé, BernardoWe present a novel method to measure precisely the relative spectral response of the fluorescence telescopes of the Pierre Auger Observatory. We used a portable light source based on a xenon flasher and a monochromator to measure the relative spectral efficiencies of eight telescopes in steps of 5 nm from 280 nm to 440 nm. Each point in a scan had approximately 2 nm FWHM out of the monochromator. Different sets of telescopes in the observatory have different optical components, and the eight telescopes measured represent two each of the four combinations of components represented in the observatory. We made an end-to-end measurement of the response from different combinations of optical components, and the monochromator setup allowed for more precise and complete measurements than our previous multi-wavelength calibrations. We find an overall uncertainty in the calibration of the spectral response of most of the telescopes of 1.5% for all wavelengths; the six oldest telescopes have larger overall uncertainties of about 2.2%. We also report changes in physics measurables due to the change in calibration, which are generally small.
- The hadronic interaction model Sibyll – past, present and futurePublication . Engel, Ralph; Riehn, Felix; Fedynitch, Anatoli; Gaisser, Thomas K.; Stanev, TodorSibyll is one of the first microscopic interaction models that was specifically developed for interpreting cosmic ray data. It combines non-perturbative concepts of simulating hadronic particle production with predictions derived from perturbative QCD calculations, focusing on forward particle production of relevance in studying cosmic ray interactions. In this contribution we briefly recall the history of Sibyll and then, in this context, describe improvements made in the different versions of the Sibyll model. The discussion focuses on the basic concepts and ideas of these improvements rather than going into detail or giving a comprehensive description of the models. We also discuss shortcomings, conceptual problems, and uncertainties in modeling hadronic interactions and make some suggestions how to address these open questions in the future.
- The hadronic interaction model SIBYLL 2.3c and Feynman scalingPublication . Riehn, Felix; Dembinski, Hans P.; Engel, Ralph; Fedynitch, Anatoli; Gaisser, Thomas K.; Stanev, TodorThe Monte Carlo model Sibyll has been designed for efficient simulation of hadronic multiparticle production up to the highest energies as needed for interpreting cosmic ray measurements. For more than 15 years, version 2.1 of Sibyll has been one of the standard models for air shower simulation. Motivated by data of LHC and fixed-target experiments and a better understanding of the phenomenology of hadronic interactions, we have developed an improved version of this model, version 2.3, which has been released in 2016. In this contribution we present a revised version of this model, called Sibyll 2.3c, that is further improved by adjusting particle production spectra to match the expectation of Feynman scaling in the fragmentation region. After a brief introduction to the changes implemented in Sibyll 2.3 and 2.3c with respect to Sibyll 2.1, the current predictions of the model for the depth of shower maximum, the number of muons at ground, and the energy spectrum of muons in extensive air showers are presented.