Role of $\omega$-meson exchange in scaling of the $\gamma p\to {\pi }^{0}p$ process from a Regge-type model with resonances

Abstract

The scaling of photoproduction $\gamma p\to {\pi }^{0}p$ is investigated in the Reggeized model with $N^{\ast }$ and $\Delta$ resonances included to describe resonance peaks up to photon energy $E_{\gamma }$= 3 GeV. Given the $t$-channel exchanges $\rho (770)+\omega (780)+b_1(1235)+h_1(1170)$ 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 $s^{7}d\sigma /dt$ 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 $\omega$ exchange that originates from the zeros of the trajectory ${\alpha }_{\omega }(t)=0$ in the canonical phase, $\frac{1}{2}(-1+e^{-i\pi {\alpha }_{\omega }(t)})$.

Comments: 5 pages, 2 tables, 5 figures