A ug 2 01 6 Role of ω-meson exchange in scaling of the γp → π 0 p process from a Regge-type model with resonances

The scaling of photoproduction γp → πp is investigated in the Reggeized model with N∗ and ∆ resonances included to describe resonance peaks up to photon energy Eγ= 3 GeV. Given the t-channel exchanges ρ(770) + ω(780) + b1(1235) + h1(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 sdσ/dt are reproduced to agree with the recent JLab data, revealing the production mechanism of the big bump structure around W ≈ 2.2 GeV by the deep-dip pattern of the ω exchange that originates from the zeros of the trajectory αω(t) = 0 in the canonical phase, 1 2 (−1 + eω).