Role of $ω$-meson exchange in scaling of the $γp\toπ^0 p$ process from a Regge-type model with resonances
The scaling of photoproduction $γp\toπ^0 p$ is investigated in the Reggeized model with $N^*$ and $Δ$ resonances included to describe resonance peaks up to photon energy $E_γ$= 3 GeV. Given the $t$-channel exchanges $ρ(770)+ω(780)+b_1(1235)+h_1(1170)$ Reggeized for the background contribution, the resonances of the Breit-Wigner form are introduced to agree with cross sections for total, differential and beam asymmetry in the low energy region. The scaled differential-cross sections $s^7{dσ/ dt}$ 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 $ω$ exchange that originates from the zeros of the trajectory $α_ω(t)=0$ in the canonical phase, ${1\over2}(-1+e^{-iπα_ω(t)})$.