ωN scattering length from ω photoproduction on the proton near the reaction threshold

Photoproduction of the omega meson on the proton has been experimentally studied near the threshold. The total cross sections are determined at incident energies ranging from 1.09 to 1.15 GeV. The 1/2 and 3/2 spin-averaged scattering length a(omega p) and effective range r(omega p) between the CO meson and proton are estimated from the shape of the total cross section as a function of the incident photon energy: a(omega p) = (-0.97(-0.16stat)-(+0.16stat+0.03syst)(0.00syst)) + i(0.07(-0.14stat-0.09syst)(+0.15stat+0.17syst)) fm and r(omega p) = (+2.78 (+0.67stat+0.11syst)(-0.54stat-0.12syst)) + i(-0.01(-0.50stat-0.00syst)(+0.46stat+0.06syst)) resulting in a repulsive force. The real and imaginary parts for a(omega p) and r(omega p) are determined separately for the first time. A small P-wave contribution does not affect the obtained values.