Measurement of Energy Spectrum and Elemental Composition of PeV Cosmic Rays: Open Problems and Prospects

Cosmic rays represent one of the most important energy transformation processes of the universe. They bring information about the surrounding universe, our galaxy, and very probably also the extragalactic space, at least at the highest observed energies. More than one century after their discovery, we have no definitive models yet about the origin, acceleration and propagation processes of the radiation. The main reason is that there are still significant discrepancies among the results obtained by different experiments located at ground level, probably due to unknown systematic uncertainties affecting the measurements. In this document, we will focus on the detection of galactic cosmic rays from ground with air shower arrays up to 1018 eV. The aim of this paper is to discuss the conflicting results in the 1015 eV energy range and the perspectives to clarify the origin of the so-called `knee’ in the all-particle energy spectrum, crucial to give a solid basis for models up to the end of the cosmic ray spectrum. We will provide elements useful to understand the basic techniques used in reconstructing primary particle characteristics (energy, mass, and arrival direction) from the ground, and to show why indirect measurements are difficult and results are still conflicting.

First results of LHAASO

The Large High Altitude Air Shower Observatory (LHAASO) has recently published the first results, including the discovery of 12 ultrahigh-energy gamma-ray sources (with emission above 100[Formula: see text]TeV) above [Formula: see text] confidence level and a detailed analysis of Crab Nebula. This contribution gives a brief introduction to the LHAASO experiment and its recent discoveries.

Chapter 1 LHAASO Instruments and Detector technology

The Large High Altitude Air Shower Observatory ( LHAASO ) ( Fig. 1 ) is located at Mt. Haizi (4410 m a.s.l., 600 g/cm2, 29◦ 21’ 27.56” N, 100◦ 08’ 19.66” E) in Daocheng, Sichuan province, P.R. China. LHAASO consists of 1.3 km2 array ( KM2A ) of electromagnetic particle detectors ( ED ) and muon detectors ( MD ), a water Cherenkov detector array ( WCDA ) with a total active area of 78,000 m2, 18 wide field-of-view air Cherenkov telescopes (WFCTA ) and a newly proposed electron-neutron detector array ( ENDA ) covering 10,000 m2. Each detector is synchronized with all the other through a clock synchronization network based on the White Rabbit protocol. The observatory includes an IT center which comprises the data acquisition system and trigger system, the data analysis facility. In the following of this Chapter, all the above mentioned components of LHAASO will be briefly described, together with infrastructure which is a fundamental component of the LHAASO observatory.

PeV Emission of the Crab Nebula: Constraints on the Proton Content in Pulsar Wind and Implications

Recently, two photons from the Crab Nebula with energy of approximately 1 PeV were detected by the Large High Altitude Air Shower Observatory (LHAASO), opening an ultrahigh-energy window for studying pulsar wind nebulae (PWNe). Remarkably, the LHAASO spectrum at the highest-energy end shows a possible hardening, which could indicate the presence of a new component. A two-component scenario with a main electron component and a secondary proton component has been proposed to explain the whole spectrum of the Crab Nebula, requiring a proton energy of 1046–1047 erg remaining in the present Crab Nebula. In this paper, we study the energy content of relativistic protons in pulsar winds using the LHAASO data of the Crab Nebula, considering the effect of diffusive escape of relativistic protons. Depending on the extent of the escape of relativistic protons, the total energy of protons lost in the pulsar wind could be 10–100 times larger than that remaining in the nebula presently. We find that the current LHAASO data allow up to (10–50)% of the spindown energy of pulsars being converted into relativistic protons. The escaping protons from PWNe could make a considerable contribution to the cosmic-ray flux of 10–100 PeV. We also discuss the leptonic scenario for the possible spectral hardening at PeV energies.

Earth-Skimming Ultrahigh Energy Tau Neutrinos Simulated with Monte Carlo Method and CONEX Code

This paper is aimed at studying the feasibility of building an Earth-skimming cosmic tau neutrinos detector, with the aim of eventually identifying the ideal dimensions of a natural site mountain-valley for the detection of very high energy neutrinos tau range from 1 0 16 eV to 1 0 20 eV , as well as possibly locate one such site in Algeria. First, a Monte Carlo simulation of the neutrino-[mountain] matter interaction as well as the resulting decay of the tau lepton is conducted to determine the optimal dimensions of the mountain as well as the location of the tau decay in the valley. Second, a CORSIKA (COsmic Ray Simulation for KAscade) simulation with the CONEX option is conducted to track the evolution of the almost horizontal air shower initiated by the tau lepton. Many particles are produced, which are part of the shower components: electrons, muons, gammas, pions, etc. The study of the spatial distribution of these particles enables the discovery of the optimal width of the valley, and consequently, the distance at which to lay the detection network.

Extensive Air Shower Reconstruction using the timing information from the RF-system of the Astroneu array

The Astroneu cosmic ray telescope is a distributed hybrid array consisting of both scintillator counters and RF antenna detectors used for the detection of extensive air showers (EAS). The array is deployed at the Hellenic Open University campus, on the outskirts of the urban area of Patras in Greece. In the present development phase, the Astroneu telescope includes two stations consisting of 3 scintillation detectors modules (SDM) and one RF antenna while a third station includes 3 particle detectors and 4 RF antennas (3SDM-4RF). In each station, the RF-detectors are operating receiving a common trigger upon a 3-fold coincidence between the particle detectors of the station. In this study we present recent results from the 3SDM-4RF autonomous station related to the estimation of the direction of the incoming cosmic air shower using only the timing information from the 4 RF detectors. The directions of the reconstructed showers using the RF timing are in agreement with the corresponding results using the SDMs timing as well as with the simulation predictions. This verifies that the RF signal emitted from EAS originating form Ultra High Energy Cosmic Rays (UHECR), can be detected even in areas with strong electromagnetic background.