Reports MoEDAL’s search for trapped magnetic monopoles in aluminum samples exposed to LHC 13 TeV pp collisions, interpreted via both Drell-Yan and photon-fusion production; no monopoles found, excluding magnetic charges at or above the Dirac charge over a probed mass range up to ~2500 GeV via production-cross-section upper limits. relevance_note: direct collider null-result bounding how readily the LHC could actually produce a magnetic monopole in the first place — the empirical check on whether the monopole-catalysis route is even reachable.
Search and null result
O-8 - MoEDAL found no trapped magnetic charge at or above one Dirac charge in 794 kg of aluminum exposed to 13 TeV LHC collisions
Calibration by two independent methods (dipole-sample superposition and long thin solenoid) agreeing within 10 percent; magnetometer response linear and charge-symmetric over 0.3-300 g_D. The trapping null itself is model-independent: it assumes only that a slow (beta ⇐ 10^-3) monopole binds strongly to aluminum nuclei.
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Limits
O-9 - MoEDAL sets 95 percent CL cross-section limits down to 11 fb and indicative mass limits of 1500-3750 GeV for LHC monopole pair production
Acceptance from Geant4 simulation of monopole energy loss and stopping (maximum ~3.8-4.5 percent depending on charge; dominant systematic the ~10 percent material-description uncertainty, growing with charge until the interpretation ceases to be meaningful at 6 g_D). Photon fusion dominates the mass bounds because its cross section exceeds Drell-Yan over most of the spin/mass range.
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A-10 - The large monopole-photon coupling makes leading-order cross sections unreliable, so the MoEDAL mass limits are indicative only
Reasoning
The trapping null and the cross-section-times-acceptance upper limits depend on the production model only through kinematics and detector acceptance. The step to a mass bound, however, requires an absolute production cross section, computed here from leading-order Feynman-like DY and gamma-gamma diagrams - ‘although the large monopole coupling to the photon places such calculations in the nonperturbative regime.’ The collaboration states the mass limits ‘are only indicative, since they rely upon cross sections computed (at leading order) using perturbative field theory when the monopole-photon coupling is too large to justify such an approach.’ The beta-dependent coupling and magnetic-moment parameter kappa variants are explored precisely to illustrate this theoretical spread (a nonperturbative alternative - thermal Schwinger production in heavy-ion collisions - is cited as a way around it). Consequence for downstream use: MoEDAL bounds how often the LHC makes monopoles only under these production models; a nonperturbatively suppressed (e.g. exponentially suppressed Schwinger-like) production rate would evade the mass limits while leaving the cross-section limits intact.
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