Measurement of Downward-going Milli-charged particles beyond GZK cutoff at the Pierre Auger Observatory

TL;DR

This paper investigates the potential detection of ultra-high-energy milli-charged particles originating from superheavy dark matter decay using the Pierre Auger Observatory, setting new limits and exploring their implications for cosmology.

Contribution

It provides the first constraints on MCPs beyond the GZK cutoff using 14 years of Auger data, considering a massless hidden photon interaction model.

Findings

MCPs can be directly detected with  at Auger under certain conditions.

A new excluded region in the MCP mass- parameter space is identified.

Upper limits on MCP fluxes and interaction parameters are established.

Abstract

It is assumed that superheavy dark matter particles (SHDM, $\phi$) with $\mathcal{O}$(ZeV) mass may decay to relativistic milli-charged particles (MCPs, $\chi$) via a channel $\phi\to\chi\bar{\chi}$ or $\gamma\chi\bar{\chi}$. The downward-going MCPs passing through the atmosphere can be measured by the Pierre Auger observatory (Auger). The massless hidden photon model is taken for MCPs to interact with nuclei, so that we evaluated the numbers and fluxes of expected MCPs at Auger assuming 14 years of Auger data. The hybrid data of Auger was fitted with the flux of UHE MCPs exceeding GZK-cutoff energy. Then the corresponding upper limits on $\epsilon^2$ are calculated at 90\% C. L.. These results indicate that MCPs can be directly detected with $\epsilon^2\gtrsim 2\times10^{-6}$ at Auger, when $m_{\phi}=2\times10^{21}$ eV and $\tau_{\phi}=10^{27}$ s. And a new region of 10$^{9.6}$ < $m_{MCP}$ < 10$^{11.6}$ eV and $\epsilon$ > $2.12\times10^{-2}$ is ruled out in the $m_{MCP}$-$\epsilon$ plane with 14 years of Auger data. These results indicate potential existence of MCPs and SHDM in the Universe.