Search for Magnetic-Monopole Production by 300-GeV Protons

In a search for magnetic monopoles, a steel beam dump has been exposed to 3.4 × ${10}^{16}$ protons of 300 GeV energy at the National Accelerator Laboratory. The search apparatus employed an 80-kG solenoid 50 cm long capable of extracting a monopole and accelerating it through a series of thin scintillation counters. A monopole would have been identified by its energy loss and range in the scintillators. No monopoles with magnetic charges in the interval from $\frac{1}{6}$ to 24 times the Dirac magnetic charge were found. The upper limit at a 95% confidence level for the cross section per nucleon on iron is 6 × ${10}^{-42\mathrm{}}$ ${\mathrm{cm}}^2$.