EAS age determination from the study of the lateral distribution of charged particles near the shower axis with the ARGO-YBJ experiment

TL;DR

This study uses the ARGO-YBJ detector's detailed measurements of charged particle distributions near the shower axis to determine the age of extensive air showers, providing insights into cosmic ray composition in the 50 TeV to 10 PeV range.

Contribution

It introduces a method to estimate EAS age using the lateral density profile close to the shower axis with high-altitude detector data.

Findings

Effective EAS age determination from ground measurements.

Sensitivity of age parameter to primary cosmic ray mass composition.

Successful analysis over a wide energy range (50 TeV - 10 PeV).

Abstract

The ARGO-YBJ experiment, a full coverage extensive air shower (EAS) detector located at high altitude (4300 m a.s.l.) in Tibet, China, has smoothly taken data, with very high stability, since November 2007 to the beginning of 2013. The array consisted of a carpet of about 7000 m$^2$ Resistive Plate Chambers (RPCs) operated in streamer mode and equipped with both digital and analog readout, providing the measurement of particle densities up to few particles per cm$^2$. The unique detector features (full coverage, readout granularity, wide dynamic range, etc) and location (very high altitude) allowed a detailed study of the lateral density profile of charged particles at ground very close to the shower axis and its description by a proper lateral distribution function (LDF). In particular, the information collected in the first 10 m from the shower axis have been shown to provide a very effective tool for the determination of the shower development stage ("age") in the energy range 50 TeV - 10 PeV. The sensitivity of the age parameter to the mass composition of primary Cosmic Rays is also discussed.