Measurement of γγ → pp̄ production at Belle

Abstract A high precision study of the process γ γ → p p ¯ has been performed using a data sample of 89 fb −1 collected with the Belle detector at the KEKB e + e − collider. The cross section of p p ¯ production has been measured at two-photon center-of-mass (c.m.) energies between 2.025 and 4.0 GeV and in the c.m. angular range of | cos θ ∗ | 0.6 . Production of γ γ → η c → p p ¯ is observed and the product of the two-photon width of the η c and its branching ratio to p p ¯ is determined.