Most precise measurement of the cosmic-ray energy spectrum at ultra-high energies

2020

Recently, the Pierre Auger Collaboration has presented the most precise measurement of the cosmic-ray (CR) energy spectrum at ultra-high energies using the events recorded over more than 14 years by the surface detector (SD). The data set consists on 215,030 events with zenith angles below 60° and energies larger than 2.5x10 ¹⁸ eV.

The energy spectrum plays a key role in understanding CRs and its measurement is particularly challenging given the rapid fall off of the flux with energy. A key feature of the work is that the estimates of the energies are independent of assumptions about the unknown hadronic physics or of the primary mass composition. This is attained setting the energy scale of the Observatory with the calorimetric measurement of the shower energy performed with the fluorescence detector (FD). Moreover, the measurement is performed in a regime of full efficiency of the array, reducing the calculation of the exposure to a geometrical problem and live-time of the detector.

The Pierre Auger Collaboration, Phys. Rev. Lett. 125, 121106 (2020)

Cosmic rays air showers properties and characteristics of the emitted radio signals using analytical approaches and full Monte Carlo simulations

26 Mar 2020

Cosmic rays have been a hot topic for the Astroparticle Physics community, since discovered in 1912. After over a century and many efforts from scientists worldwide we know now that the most energetic particles observed on Earth, the ultra-high energy cosmic rays (UHECRs), have an extragalactic source. Where, how and what exactly accelerates them? These questions remain still mysterious nowadays. The extensive air showers (EAS) developed by cosmic rays (CRs) in the Earth's atmosphere are at this moment the most resourceful subject of study for researchers who make efforts to better understand these fascinating particles. However, the detection and study of EAS is not at all an easy task. Because the Earth's atmosphere is being used as a giant detector of cosmic rays, EAS develop differently based on primary particle energy and mass, incoming direction and atmospheric environment at a given location. In this paper we look at the development of EAS from two different, but complementary perspectives. First, we show how the main parameters of the showers modify, as function of the primary properties, by multiple longitudinal profiles simulated with CONEX, for different sets of CR parameters (energy, mass, direction of propagation). Next, we look at the radio signals emitted by EAS, which develop at the Pierre Auger Observatory location, by using a simplified v✕B model to describe the geomagnetic emission, and sophisticated simulations with the CoREAS option in the CORSIKA Monte Carlo code, who treat the full radio emission released by an air shower. Some of the results presented in this paper are included in an open source graphical user interface (GUI) application, EAS Browser v2.0.

P.G. Isar, D. Hirnea, A. Jipa, Rom.Rep.Phys. 72 (2020) 1, 301)