Investigating convergence of the reaction $\gamma p\to\pi^\pm\Delta$ and tensor meson $a_2$ exchange at high energy

TL;DR

This paper models high-energy gamma-proton reactions involving pion and tensor meson exchanges using a Regge approach, highlighting the importance of tensor meson $a_2$ exchange in matching experimental data.

Contribution

It introduces a new $a_2N\Delta$ coupling Lagrangian and demonstrates the significance of $a_2$ exchange in high-energy reaction modeling.

Findings

$a_2$ exchange is crucial for accurate cross section predictions.

The model successfully reproduces experimental data up to 16 GeV.

A new coupling constant for $a_2N\Delta$ was deduced from duality and vector dominance.

Abstract

A Regge approach to the reaction processes $\gamma p\to\pi^-\Delta^{++}$ and $\gamma p\to\pi^+\Delta^0$ is presented for the description of existing data up to $E_\gamma= 16$ GeV. The model consists of the $t$-channel $\pi(139)+\rho(775)+a_2(1320)$ exchanges which are reggeized from the relevant Born amplitude. Discussion is given on the minimal gauge prescription for the $\pi$ exchange to render convergent the divergence of the $u$-channel $\Delta$-pole in the former process. A new Lagrangian is constructed for the $a_2N\Delta$ coupling in this work and applied to the process for the first time with the coupling constant deduced from the duality plus vector dominance. It is shown that, while the $\pi$ exchange dominates over the process, the role of the $a_2$ exchange is crucial rather than the $\rho$ in reproducing the cross sections for total, differential, and photon polarization asymmetry to agree with data at high energy.