Final results of magnetic monopole searches with the MACRO experiment

TL;DR

The MACRO experiment conducted comprehensive searches for GUT magnetic monopoles in cosmic radiation, setting the most stringent flux limits to date across a broad velocity range, with no monopoles detected.

Contribution

This paper reports the final results of the MACRO experiment's direct search for magnetic monopoles, establishing the lowest flux limits and covering the entire expected velocity range.

Findings

No magnetic monopoles detected in the search.

Established flux upper limit at 1.4×10⁻¹⁶ cm⁻² s⁻¹ sr⁻¹.

Results are below the Parker bound across all velocities.

Abstract

We present the final results obtained by the MACRO experiment in the search for GUT magnetic monopoles in the penetrating cosmic radiation, for the range $4\times 10^{-5}< \beta < 1$. Several searches with all the MACRO sub-detectors (i.e. scintillation counters, limited streamer tubes and nuclear track detectors) were performed, both in stand alone and combined ways. No candidates were detected and a 90% Confidence Level (C.L.) upper limit to the local magnetic monopole flux was set at the level of $1.4\times 10^{-16}$ cm$^{-2}$ s$^{-1}$ sr$^{-1}$. This result is the first experimental limit obtained in direct searches which is well below the Parker bound in the whole $\beta$ range in which GUT magnetic monopoles are expected.