A Method to Search for Correlations of Ultra-High Energy Cosmic-Ray Masses With the Large-Scale Structures in the Local Galaxy Density Field

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.

Zenith angle distribution of cosmic ray showers measured with the Yakutsk array and its application to the analysis of arrival directions in equatorial coordinates

“…The first level involves the coincidence of signals from two scintillation counters at a station within 2 µs; the second level involves the coincidence of signals from at least three nearby stations within 40 µs [2,9]. Several algorithms have been developed in the Yakutsk array group to evaluate the energy of the primary particle initiating EAS [15][16][17][18]. In this paper, the most recent method proposed in [19] is used.…”

Zenith angle distribution of cosmic ray showers measured with the Yakutsk array

“…Several algorithms have been developed to evaluate the energy of the primary particle initiating EAS [19,20,21,22]. In this paper, two conventional methods proposed in [23] and [24] are used.…”