Speaker
Description
High-statistics total cross sections for the vector meson photoproduction at the threshold: $\gamma p\to \omega p$ (from A2 at MAMI and ELPH), $\gamma p\to \phi p$ (from CLAS6 at JLab) and $\gamma p\to J/\psi p$ (from GlueX at JLab) 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 $\phi$-meson compared to the typical hadron size of approximately
$1~\mathrm{fm}$ indicates that the proton is more transparent for the $\phi$-meson compared to the $\omega$-meson and is much less transparent than the $J/\psi$-meson. The extended analysis of $\Upsilon$-meson
photoproduction using quasi-data from the QCD approach is in perfect agreement with the light-meson findings using experimental data.
Recent high-statistical $J/\psi$ photoproduction cross sections measured by the GlueX Collaboration allow us to search for the exotic $P_c(4312)$ state observed by the LHCb Collaboration. The fits show that destructive
interference involving a $S$ wave resonance and associated nonresonance background produces a sharp dip structure approximately $77~\mathrm{MeV}$ below the LHCb mass, in the same location as a similar structure is seen in the data. The interference between open charm and gluon exchange may (by some accident) produce a dip, but there is room for resonance.
Future high-quality experiments by EIC and EicC will have the opportunity to evaluate cases for $J/\psi$- and $\Upsilon$-mesons. It allows us to understand the dynamics of $c\bar{c}$ and $b\bar{b}$ production at the threshold and to look for the effect of LHCb $P_c(4312)$. The ability of J-PARC to measure $\pi^-p\to \phi n$ and $\pi^-p\to J/\psi n$, which are free from the VMD model, is evaluated.
