La lunghezza di attenuazione dei muoni nelle cascate ad alta energia in atmosfera misurate da IceTop

Cosmic rays are nuclei of various chemical elements, produced in astrophysical environments, that propagate through the space. When a primary particle arrives in the atmosphere, it interacts with it creating an Extensive Air Shower (EAS) composed of many particles, among which electrons and muons. IceTop, the experiment on which this project is based, has an energy range between 1 PeV and 1 EeV. IceTop is the surface component of the IceCube detector, a neutrino observatory constructed in Antarctica. IceTop consists of 81 stations: each station consists of two ice Cherenkov tanks and each tank contains two Digital Optical Modules (DOMs). A trigger occurs when the signal in one of the DOMs in a tank has passed the discriminator threshold. The total charge collected constitutes the tank's signal and there are two types of signal: HLC and SLC. Electrons and muons may give both types of signal. The shower has to be interpreted: CORSIKA is a Monte Carlo code for detailed simulation of extensive air showers initiated by high energy cosmic ray particles. A hadronic interaction model is used to describe the interaction of cosmic rays with the atmosphere. The aim of this project was to validate the model EPOS-LHC using the attenuation length of muons, αμ(r). The attenuation length measures the rate of absorption by the atmosphere of the particles. Simulation data for proton and iron obtained using the model EPOS-LHC were provided. From these data the attenuation length for proton and iron has been obtained. The attenuation length for the experimental data has also been obtained and finally these values have been compared. To start the procedure different ranges have been defined and the energy of the experimental data has been reconstructed knowing the relation between the energy of the simulation data and the parameter S125 of the shower. Afterwards to obtain the attenuation length the 2-dimensional histograms have been obtained (radial distance from the core on the X-axis and the signal on the Y-axis). The two types of signal have been included. Then seven 1-dimensional histograms of signal have been found from each 2-dimensional histogram with energy range 3. The method to separate the signal produced by muons from the signal produced by electrons has been decided and 0.7 VEM is the value of the separation. The muon density on the ground has been calculated for each shower and the 1-dimensional histograms of muon density have been obtained. After the fits (X coordinates are the secant of the mean of the zenith angle histograms, Y coordinates are the mean of the muon density histograms) have been done. There is a relation ρμ(r,θ) = ρ0μ(r)*e(−X0 secθ/αμ(r)) between the muon density on the ground and the zenith angle of the primary particle and αμ is a parameter of the fit. Various fits had some problems so it has been decided to do again the fits using the median of the muon density histograms. The fits improved but there are still some problems, probably due to the signal cut. The αμ values have been compared and it has become clear that the model EPOS-LHC describes the experimental data only in some radial distance ranges. To understand if the problems found are due to the model EPOS-LHC or to the cut of the signal produced by muons, the αμ values obtained from EPOS-LHC and SIBYLL 2.3 (it has been studied from another student in the past) have been compared. It has been understood that probably the problems are due to the signal cut.