Calculation of conventional and prompt lepton fluxes at very high energy

Abstract

An efficient method for calculating inclusive conventional and prompt atmospheric leptons fluxes is presented. The coupled cascade equations are solved numerically by formulating them as matrix equation. The presented approach is very flexible and allows the use of different hadronic interaction models, realistic parametrizations of the primary cosmic-ray flux and the Earth's atmosphere, and a detailed treatment of particle interactions and decays. The power of the developed method is illustrated by calculating lepton flux predictions for a number of different scenarios. Cosmic rays entering the Earth's atmosphere produce a multitude of secondary particles in interactions with air nuclei. Some of the secondary particles decay into muons and neutrinos, which are not absorbed in the atmosphere and can reach particle detectors at ground level. The spectra of these leptons contains not only information about the primary cosmic rays, but also about the particle physics of their production and the properties of the traversed atmosphere. Furthermore, searches for high- energy neutrinos from astrophysical sources have to cope with a large flux of atmospheric leptons as background. A better understanding of this flux, in particular its dependence on zenith angle and the changing properties of the atmosphere will help to develop improved methods to identify astrophysical neutrino fluxes and also contribute to a better understanding of hadronic interactions at high energy.