Puzzle for the Vector Meson Threshold Photoproduction

Abstract

High-statistics total cross sections for the vector meson photoproduction at the threshold: $γp\toωp$ (from A2 at MAMI, ELPH, and CBELSA/TAPS), $γp\to ϕp$ (from CLAS and LEPS), and $γp\to J/ψp$ (from GlueX) allow one to extract the absolute value of vector meson nucleon scattering length using Vector Meson Dominance (VMD) model. The ``young'' vector meson hypothesis may explain the fact that the obtained scattering length value for the nucleon $ϕ$-meson compared to the typical hadron size of approximately $\sim1~\mathrm{fm}$ indicates that the proton is more transparent for the $ϕ$-meson compared to the $ω$-meson and is much less transparent than the $J/ψ$-meson. The extended analysis of $Υ$-meson photoproduction using quasi-data from the QCD approach is in perfect agreement with the light-meson findings using experimental data. Future high-quality experiments by EIC and EicC will have the opportunity to evaluate cases for $J/ψ$- and $Υ$-mesons. It allows one to understand the dynamics of $c\bar{c}$ and $b\bar{b}$ production at the threshold. The ability of J-PARC to measure $π^- p\to ϕn$ and $π^-p\to J/ψn$, which are free from the VMD model, is considered.