First search for magnetic monopoles through the Schwinger mechanism

Magnetic monopoles are hypothetical fundamental particles predicted in several theories beyond the standard model, however they have never been experimentally detected. The Schwinger mechanism predicts that an extremely strong magnetic field would produce isolated magnetic charges, if they exist. Looking for the existence of magnetic monopoles via the Schwinger mechanism had not been attempted before, but it is advantageous, owing to the possibility of calculating its rate through semi-classical techniques without perturbation theory. This paper focuses on the first search for magnetic monopoles produced by the Schwinger mechanism in heavy-ion collisions. It was carried out by the MoEDAL experiment, whose trapping detectors were exposed to 0.235 nb$^{−1}$ of Pb-Pb collisions with 5.02 TeV energy per collision at the LHC, that provided the strongest known magnetic fields in the universe. A superconducting quantum interference device magnetometer scanned these detectors for the presence of magnetic charge. Magnetic monopoles with 1, 2 and 3 Dirac charges and masses up to 75 GeV were excluded by the analysis. This analysis, which has been published in the journal Nature, provided a lower mass limit for finite-size magnetic monopoles from a collider search and greatly extended previous mass bounds.