Ing. Jakub Vícha, Ph.D.
Dr. Alexey Yushkov
The group is primarily involved in data analysis, operation, and upgrade of the Pierre Auger Observatory (www.auger.org), the world's largest cosmic-ray detector spread over 3000 km2 on a high plain in Mendoza province, Argentina. The principal goal of the Observatory is to discover powerful astrophysical objects and phenomena capable of accelerating ultra-high-energy cosmic rays (UHECR) to energies beyond 1020 electronvolt (about 1.6 Joule), millions of times surpassing energies achieved at the Large Hadron Collider (CERN).
Properties of UHECRs can be studied only indirectly from observations of cascades of billions of secondary particles (air showers) generated by a primary particle interaction in the upper layers of the atmosphere. At the Pierre Auger Observatory, air-shower detection is performed by sampling the lateral distribution of secondary particles with surface water Cherenkov detectors and observing the longitudinal shower development in the atmosphere with fluorescence telescopes, which can be operated only during clear and dark nights. Using the atmosphere as a giant calorimeter, the fluorescence technique provides a calorimetric estimate of the UHECR energy for a small fraction of the data. After calibrating signals produced by air-shower particles in the Surface Detector with the fluorescence calorimetric energy estimate, the common energy scale can eventually be used for the whole data set.
In contrast to this method, the estimation of primary particle mass from the longitudinal and lateral characteristics of air showers suffers from considerable uncertainties in the modelling of hadronic interactions, which uses extrapolation of measurements at the Large Hadron Collider and other accelerator facilities to much higher energies and uncharted phase spaces. Establishing the mass composition is paramount for astrophysical interpretation of the features observed in the UHECR energy spectrum and arrival directions. Therefore, developing mass composition analyses with reduced sensitivity to the systematic uncertainties in the air-shower simulations or providing insights into the shortcomings of the modern hadronic interaction models are of the utmost importance for the UHECR field.
Our group is deeply engaged in this topic, authoring and co-authoring several methods in which the Surface and Fluorescence Detector data are used to determine the mass composition with reduced systematic uncertainties stemming from modern hadronic interaction models and concurrently to reveal flaws of these models. Further, the group has leading positions in the energy spectrum measurements using the Cherenkov technique and the reconstruction of atmospheric muon production depth using underground muon detectors. Other topics include the UHECR acceleration, propagation and anisotropies in the arrival directions; the influence of modifications of hadronic interaction parameters on the air-shower development; application of machine learning for estimation of characteristics of the muon shower component; improvements in the event reconstruction and development of additional event reconstruction methods; searches for showers with anomalous profiles and upward-going showers with the Fluorescence Detector. We participate in the work of the joint mass composition group of the Pierre Auger and Telescope Array Collaborations.
Our team is the principal contributor to the production, expansion, maintenance, and documentation of the general-purpose air-shower simulation library, which the Pierre Auger Collaboration uses in multiple publications, PhD theses, and ongoing analyses. The group members coordinate the four tasks within the Pierre Auger Observatory: fluorescence detector, air-shower physics, mass composition, and Monte Carlo simulations.
In addition, we are currently investigating the origin of seasonal variation in multi-muon events observed by the NO𝜈A Near Detector at Fermilab and estimations of the invisible energy and muon content from the data of the KASCADE experiment.