Azimuthal modulation of cosmic ray flux as an effect of geomagnetic field in the ARGO-YBJ experiment

TL;DR

This paper investigates how the Earth's geomagnetic field influences the azimuthal distribution of cosmic ray showers detected by ARGO-YBJ, revealing effects on secondary particle distribution and detector efficiency.

Contribution

It provides a detailed analysis of geomagnetic effects on cosmic ray shower azimuthal distributions using Monte Carlo simulations, enhancing understanding of observational biases.

Findings

Azimuthal non-uniformity correlates with geomagnetic influence.

Geomagnetic effects vary with shower zenith angle.

Simulation confirms the impact on detector trigger efficiency.

Abstract

The geomagnetic field causes not only the East-West effect on the primary cosmic rays but also affects the trajectories of the secondary charged particles in the shower, causing their lateral distribution to be stretched along certain directions. Thus both the density of the secondaries near the shower axis and the trigger efficiency of a detector array decrease. The effect depends on the age and on the direction of the showers, thus involving the measured azimuthal distribution. Here the non-uniformity of the azimuthal distribution of the reconstructed events in the ARGO-YBJ experiment is deeply investigated for different zenith angles on the light of this effect. The influence of the geomagnetic field as well as geometric effects are studied by means of a Monte Carlo simulation.