Helicity Softer Dipole Pomeron Model for Vector Meson Photoproduction by Arbitrarily Polarized Photons

Abstract

Understanding the spin dynamics of strong interactions from the nonperturbative to the perturbative regime remains a challenge. Regge pole theory offers a phenomenological framework, but existing models fail to simultaneously describe cross sections and polarization observables. Here we present a model with the Softer Dipole Pomeron--a dipole Pomeron with intercept $α(0)<1$--based on the Regge theory framework for vector meson photoproduction by arbitrarily polarized photons at energies ranging from high down to the production threshold. The accurate helicity amplitude is constructed with free trajectory parameters. This model compatibly describes the integrated and differential cross sections and the spin-density matrix elements of $ρ^{0}$ photoproduction, by fitting it synchronously to three categories of data . The agreement of our model with experimental data remarkably improves upon previous models. Predictions for circular SDMEs are also made. This model provides essential insight into the spin dynamics of nonperturbative QCD accessible at future experiments. It also underpins our proposed novel cosmic-photon polarimetry.