Role of $\omega$-meson exchange in scaling of the $\gamma p\to\pi^0 p$ process from the Regge model with resonances
We investigate photoproduction of neutral pion process $\gamma p\to\pi^0 p$ with $N^*$ and $\Delta$ resonances included in the Regge theory up to photon energy $E_\gamma$= 3 GeV. Given the Regge pole exchanges $\rho(770)+\omega(780)+b_1(1235)+h_1(1170)$ for the background contribution which agrees with high energy data in the Regge realm, the resonances of the Breit-Wigner form are introduced to estimate total and differential cross sections together with beam asymmetry $\Sigma$. The differential cross sections $s^7{d\sigma/ dt}$ scaled by energy are reproduced to agree with the recent JLab data, revealing the production mechanism of the big bump structure around $W\approx 2.2$ GeV by the deep-dip pattern of the $\omega$ exchange that originates from the zeros of the trajectory $\alpha_\omega(t)=0$ in the canonical phase, ${1\over2}(-1+e^{-i\pi \alpha_{\omega}(t)})$. The scaled cross sections for $\gamma n\to\pi^0 n$ are presented for comparison.