Atmospheric Lepton Fluxes via Two-Dimensional Matrix Cascade Equations

TL;DR

This paper introduces a 2D extension to the MCEq code for modeling atmospheric lepton fluxes, enabling efficient 3D calculations that improve accuracy at lower energies, validated against CORSIKA simulations.

Contribution

The paper presents a novel 2D numerical approach for atmospheric cascade modeling that incorporates lateral development, enhancing the accuracy of lepton flux predictions at low energies.

Findings

2D MCEq accurately models angular distributions of atmospheric leptons.

Benchmark comparisons show agreement with CORSIKA simulations.

Enables efficient 3D atmospheric neutrino flux calculations.

Abstract

The atmospheric lepton fluxes play a crucial role in many particle and astroparticle physics experiments, e.g. in establishing the neutrino signal and the muon background for neutrino oscillation measurements, or the atmospheric background for astrophysical neutrino searches. The Matrix Cascade Equations (MCEq) code is a numerical tool used to model the atmospheric lepton fluxes by solving a system of coupled differential equations for particle production, interaction, and decay at extremely low computational costs. Previously, the MCEq framework only accommodated longitudinal development of air showers, an approximation that works well for neutrino and muon fluxes at high energies (O(10 GeV) and above). However, for accurate calculations of atmospheric lepton angular distributions at lower energies, the lateral component of hadronic cascades becomes significant, necessitating three-dimensional calculation schemes. We introduce "2D MCEq", an efficient numerical approach for combined longitudinal and angular evolution of air showers that retains the low computational complexity. The accuracy of the "2D MCEq" is affirmed by its benchmark comparison with the standard Monte Carlo code CORSIKA. This study paves the way for efficient three-dimensional calculations of atmospheric neutrino fluxes.