Holmlid has seen mesons produced in his experiment. This is called magnetic monopoles catalyzed nucleon decay Seeing protons and neutrons turn into mesons is a test for the existence of the monopole.
See https://en.wikipedia.org/wiki/Proton_decay "Some beyond-the-Standard Model grand unified theories (GUTs) explicitly break the baryon number symmetry, allowing protons to decay via the Higgs particle, magnetic monopoles or new X bosons. Proton decay is one of the few unobserved effects of the various proposed GUTs. To date, all attempts to observe these events have failed." Holmlid has seen 12 billion mesons produce with each laser shot.
