A method to search for correlations of ultra-high energy cosmic ray masses with the large scale structures in the local galaxy density field

TL;DR

This paper introduces a novel non-parametric statistical method combining arrival direction analysis and EAS data to identify correlations between UHECR mass composition and large-scale cosmic structures, demonstrated on Yakutsk array data.

Contribution

It presents a new approach using the Wilcoxon signed-rank test to detect differences in cosmic ray mass composition based on arrival directions and EAS measurements.

Findings

Potential to distinguish mass composition differences from different sources.

Application to Yakutsk data shows feasibility of the method.

Method can identify correlations with large-scale structures.

Abstract

One of the main goals of investigations using present and future giant extensive air shower (EAS) arrays is the mass composition of ultra-high energy cosmic rays (UHECRs). A new approach to the problem is presented, combining analysis of arrival directions with the statistical test of the paired EAS samples. An idea of the method is to search for possible correlations of UHECR masses with their separate sources, for instance, if there are two sources in different areas of the celestial sphere injecting different nuclei, but fluxes are comparable so that arrival directions are isotropic, the aim is to reveal a difference in the mass composition of CR fluxes. The method is based on a non-parametric statistical test -- the Wilcoxon signed-rank routine -- which does not depend on the populations fitting any parameterized distributions. Two particular algorithms are proposed: first, using measurements of the depth of EAS maximum position in the atmosphere; and second, relying on the age variance of air showers initiated by different primary particles. The formulated method is applied to the Yakutsk array data, in order to demonstrate the possibility of searching for a difference in average mass composition of the two UHECR sets, arriving particularly from the supergalactic plane and a complementary region.