Measurement of the cross-section for the process gamma gamma -> p(p)over-bar root s(ee)=183-189 GeV at LEP

The exclusive production of proton-antiproton pairs in the collisions of two quasi-real photons has been studied using data taken at rootS(ee) = 183 GeV and 189 GeV with the OPAL detector at LEP. Results are presented for p (p) over bar invariant masses, W, in the range 2.15 < W < 3.95 GeV. The cross-section measurements are compared with previous data and with recent analytic calculations based on the quark-diquark model.