Search for ultrarelativistic magnetic monopoles with the Pierre Auger Observatory

TL;DR

This paper reports a search for ultra-relativistic magnetic monopoles using the Pierre Auger Observatory, setting new upper limits on their flux and improving previous constraints by an order of magnitude.

Contribution

First search for ultra-relativistic magnetic monopoles with a UHECR detector, providing the most stringent flux limits to date.

Findings

No candidate monopoles detected in data from 2004-2012.

Established upper limits on monopole flux ranging from 10^{-19} to 2.5×10^{-21} (cm^2 sr s)^{-1}.

Results significantly improve previous limits by up to an order of magnitude.

Abstract

We present a search for ultra-relativistic magnetic monopoles with the Pierre Auger Observatory. Such particles, possibly a relic of phase transitions in the early universe, would deposit a large amount of energy along their path through the atmosphere, comparable to that of ultrahigh-energy cosmic rays (UHECRs). The air shower profile of a magnetic monopole can be effectively distinguished by the fluorescence detector from that of standard UHECRs. No candidate was found in the data collected between 2004 and 2012, with an expected background of less than 0.1 event from UHECRs. The corresponding 90% confidence level (C.L.) upper limits on the flux of ultra-relativistic magnetic monopoles range from $10^{-19}$ (cm$^{2}$ sr s)$^{-1}$ for a Lorentz factor $\gamma=10^9$ to $2.5 \times10^{-21}$ (cm$^{2}$ sr s)$^{-1}$ for $\gamma=10^{12}$. These results - the first obtained with a UHECR detector - improve previously published limits by up to an order of magnitude.