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 $\omega$ meson and proton are estimated from the shape of the total cross section as a function of the incident photon energy: $a_{ \omega p} = \left(-0.97^{ +0.16_{ \rm stat}}_{ -0.16_{ \rm stat}}{ }^{ +0.03_{ \rm syst}}_{ -0.00_{ \rm syst}}\right)+i \left(0.07^{ +0.15_{ \rm stat}}_{ -0.14_{ \rm stat}}{ }^{ +0.17_{ \rm syst}}_{ -0.09_{ \rm syst}}\right)$ fm and $r_{ \omega p}=\left(+2.78^{ +0.68_{ \rm stat}}_{ -0.54_{ \rm stat}}{ }^{ +0.11_{ \rm syst}}_{ -0.13_{ \rm syst}}\right)+i\left(-0.01^{ +0.46_{ \rm stat}}_{ -0.50_{ \rm stat}}{ }^{ +0.07_{ \rm syst}}_{ -0.00_{ \rm syst}}\right)$ fm, 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.
Categories: nucl-ex