Alignment of air showers produced by ultra-high energy cosmic rays at the Pierre Auger Observatory

TL;DR

This study reveals that ultra-high energy cosmic ray air showers at the Pierre Auger Observatory are aligned with the interplanetary magnetic field, indicating magnetic influence on shower particle distribution, especially during geomagnetic storms.

Contribution

It demonstrates a significant correlation between air shower directions and the interplanetary magnetic field, highlighting magnetic effects on shower development.

Findings

Thrust axis nearly transverse to IMF

Thrust value Tp ≥ 0.64 indicating strong alignment

Alignment increases during geomagnetic storms

Abstract

We show that the energy-weighted angular (zenith, azimuth) distribution of extensive air showers (EAS), produced by Ultra High Energy (UHE) cosmic rays at the Pierre Auger Observatory (PAO), has a thrust axis almost transverse to the interplanetary magnetic field (IMF), with a thrust value $Tp \geq 0.64$ ( where 1.0 means a perfect alignment and 0.5 isotropy). This behavior strongly suggests an effect of the IMF on the charged shower particles, producing additional lateral scattering. We discuss the weakening of the Earth's magnetic field during geomagnetic storms (30\% of observational time) when the IMF becomes preponderant, strengthening the alignment.