Dear Colleagues,

The cosmic ray energy spectrum spans more than 10 decades and has a surprisingly (almost) constant power-law character. Understanding this fact and discovering the mechanisms generating the energy of the cosmic ray particles which constantly bombard Earth is one of the fundamental problems of modern physics. On the one hand, bigger and more sophisticated air shower arrays are being built and, on the other hand, there is a growing interest in the construction of small local detection stations which, apart from purely scientific purposes, have a great potential educational significance, satisfying young people's scientific curiosity and developing their interest in science, and particularly in physics.

This Special Issue will be dedicated to showing the specific similarities between the symmetry of experimental solutions from both edges of the cosmic ray energy spectrum. It can generate synergy effects; for example, the networking of local small shower arrays can be used to search for new physics in the highest energy region.

We are soliciting contributions (scientific and review articles) covering a wide range of topics related to the understood symmetry and related cosmic ray physics, including (but not limited to) the following:

• The physics of the new phenomena we should be looking for at the high-energy end of the spectrum;
• The possibility of experimentally searching for new physics in cosmic rays;
• Ideas for networks of local (school-based) small shower arrays;
• Results and experiences gained from measurements in the local small cosmic ray arrays;
• New techniques for measuring extensive cosmic ray air showers in different energy ranges;
• New (low-cost) techniques/detectors and ideas of cheap measuring cosmic ray shower particles;
• Possible educational (and community) effects of implementing the local (school) cosmic ray array project on a wider scale.

Prof. Dr. Tadeusz Wibig
Guest Editor

Manuscript Submission Information

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• Cosmic rays
• Extensive air showers
• Ultra-high-energy cosmic ray phenomena
• Small local shower arrays
• Networking of distant shower arrays
• Contemporary physics education

Title: A search for cosmic ray bursts at 0.1 PeV with a small air shower array
Authors: Roger Clay; Jassimar Singh; Piotr Homola; Olaf Bar; Dmitry Beznosko; Apoorva Bhatt; Gopal Bhatta; Lukasz Bibrzycki; Nikolay Budnev; David E Alvarez-Castillo; Niraj Dhital; Alan R. Duffy; Dariusz Gora; Alok C. Gupta; Bartosz Lozowski; Mikhail V. Medvedev; Justyna Medrala; Justinya Miszczyk; Michal Niedzwiecki; Marcin Piekarczyk; Krzysztof Rzecki; Jilberto Zamora-Saa; Katarzyna Smelcerz; Karel Smolek; Tomasz Sosnicki; Jaroslaw Stasielak; Slawdomir Stuglik; Oleksandr Sushchov; Arman Tursunov
Affiliation: *University of Adelaide, North Terrace, Adelaide, South Australia 5005
Abstract: The Cosmic Ray Extremely Distributed Observatory (CREDO) pursues a global research strategy dedicated to the search for correlated cosmic rays, so-called Cosmic Ray Ensembles (CRE). Its general approach to CRE detection does not involve any a priori considerations and its search strategy encompasses both spatial and temporal correlations, on different scales. Here we search for time clustering of the cosmic ray events collected with a small sea-level extensive air shower array at the University of Adelaide. The array consists of seven one square metre scintillators enclosing an area of 10 m x 19 m. It has a threshold energy ~0.1 PeV, and records cosmic ray showers at a rate of ~6 mHz. We have examined event arrival times over a period of over two and a half years in two equipment configurations (without and with GPS timing), recording ~300k events and ~100k events. We determined the event time spacing distributions between individual events and the distributions of time periods which contained specific numbers of multiple events. We find that the overall time distributions are as expected for random events. The distribution which was chosen a priori for particular study was for time periods covering five events (four spacings). Overall, these distributions fit closely with expectation but there are two outliers of short ‘burst’ periods in data for each configuration. One of these outliers contains eight events within 48 seconds. The physical characteristics of the array will be discussed together with the analysis procedure, including a comparison between the observed time distributions and expectation based on randomly arriving events.

Title: CREDO-Maze cosmic ray mini-array for educational purposes
Authors: Tadeusz Wibig; Michał Karbowiak
Affiliation: Faculty of Physics and Applied Informatics, University of Lodz, Pomorska 149/153, 90-236 ódź, Poland.
Abstract: In attempt to satisfy young people’s scientific curiosity and develop their interest in science and in physics, modern physics in particular, to give them a real tool for investigating a phenomenon of cosmic rays, for the real observation of high energy elementary particles and for making real scientific observations, we have designed a ’minimal’ Extensive Air Shower local array that can serve these purposes. We plan to provide such arrays to as many schools as possible. Apart from the didactic ones, there are other important physical, scientific reasons for such a multiplication of detection stations. The symmetrical, uniform growth of the shower arrays is made possible by an ingenious structure of individual array providing easy and inherently obvious expandability of the whole network. A network of local mini-arrays, when it has reached an appropriate stage of development, will serve as a ’global detector’ for the search for, e.g., the Gerasimova-Zatsepin effect or Cosmic Ray Ensembles. The discovery of one or the other would have extremely important consequences for our understanding of the nature of very high energy cosmic rays. The quantitative expansion of the CREDO-Maze project forces to minimize the costs and to aim at maximal simplicity of the local mini-arrays. In this paper we describe the prototype local mini-array built at University of Lodz. It consists of four small scintillation detectors with SiPM diodes and simple trigger systems. The station is intended to work autonomously and continuously. The results are stored locally but also transmitted in packages to the central server of the CREDO Project, where they will be part of a larger data structure enabling the already mentioned physical research sensu stricto. The construction of the station electronics and the small size of the detectors allow to perform with them, after a simple software addition, other researches within the framework of physics circles and student projects. The paper will show the first test results of tests of the station. In this paper we will present some characteristics of our prototype detector.

Title: Symmetries in the superposition model of Extensive Air Shower development
Authors: Tadeusz Wibig
Affiliation: University of Lodz
Abstract: The cosmic ray flux, as we have known for almost a hundred years, includes, in addition to protons, complex atomic nuclei, up to and including iron, although we have the whole Mendeleev table there. The interaction of nuclei at very high energies is a very complex process, nevertheless from the very beginning it has been accepted that a nucleus consisting of A nucleons can be regarded with a fairly good approximation as a set of A independent and independently interacting nucleons. In this approximation, the Extensive Air Shower induced by cosmic ray iron nucleus should evolve as 56 proton showers. This symmetry makes it possible to attempt to describe Extensive Air Shower initiated by heavy nuclei in a simplified way, which greatly reduces the time needed for simulation calculations and theoretical analysis and comparison of models of shower development. The advancement of numerical methods and technologies enabling sophisticated calculations to be carried out in a reasonable amount of time has led to the development of extremely complex computer programs allowing Monte-Carlo simulations of electromagnetic-hadronic cascades which mimic the Extensive Air Shower to be performed with a high accuracy. These programs are continuously being expanded and improved and they make it possible to carry out calculations for primary energies exceeding 10$^{20}$eV, up to the highest energies observed in the Nature. On the other hand, there is a great interest recently in the calculations of showers with minimal energies reaching sizes counted in single electrons/muons on the observation level. At such low energies, these showers mostly fade out before they reach the ground level and thus what we observe are the tails of fluctuations and all observables become far from the average. Thus, the symmetry of the superposition model may not be adequate in describing these extremely small particle densities. In this paper we will present results both consistent with the superposition model and indicating the need for its modification. This modification will be proposed and tested.

Title: The pilot operation of the microNet (μNet) project
Authors: Michael Petropoulos; Apostolos Tsirigotis; Antonios Leisos
Affiliation: Physics Laboratory, School of Science and Technology, Hellenic Open University, Parodos Aristotelous 18, Perivola Patras, 26335, Greece
Abstract: μΝet aims for the deployment and long-term operation of an extensive school network of educational Cosmic Ray telescopes in the geographical area of Peloponnese. In the framework of μNet, an extended educational program will take place, encompassing educational activities for the construction, testing and operation of μCosmics (microCosmics) detectors, as well as for the remote operation of cosmic ray detection stations and astroparticle physics experimental devices deployed at the Hellenic Open University (HOU) campus. A pilot run of the μNet project started in 2020 aiming for the deployment and operation of a small school network in western Greece. In this report we present briefly the design of the μNet project and discuss the results and findings of the pilot run.