Search for Dirac Magnetic Monopoles in e+e Collisions with the OPAL Detector at LEP2

This letter describes a direct search for pair produced magnetic monopoles in e+e collisions. The analysis is based on 62.7 pb 1 of data collected with the OPAL detector at an average centre- of-mass energy of √ s= 206.3 GeV. The monopole signal was assumed to be characterized by two back-to-back particles with an anomalously high ionization energy loss dE/dx in the tracking chambers. No evidence for production of monopoles was observed. Upper limits were obtained on the magnetic monopole pair-production cross-section (σ) in the mass range 45 GeV/c2 < mM < 102 GeV/c2. The average limit is σ < 0.05 pb and is essentially independent of the magnetic monopole mass. The cross-section limit is derived at the 95% confidence level and is valid for spin-1/2 magnetic monopoles.