Differential cross sections for γγ→ p overline-p in the CM energy range from 2.0 to 3.1 GeV

Exclusive production of proton-antiproton pairs by two photon scattering at CM energies between 2.0 GeV and 3.1 GeV has been measured with the TASSO detector at the e ⁺e ^- storage ring PETRA. The angular distribution is flat within the accepted CM angular range | cos Θ ^∗|⩽0.7 . The integrated cross section (| cos Θ ^∗|⩽0.6) drops from about 4 nb at 2 GeV to less than 0.5 nb above 3 GeV. For the two-photon production of the η_c(2984) and its subsequent decay into proton-antiproton the upper limit Γ(η _c→γγ)· B(η _c→ p overlinep)<0.32 keV (95% CL) is found.