JLab and J-PARC for the J/{\ensuremathψ} Production at the Threshold

Abstract

New threshold measurements for ${\hat{I}}^{3}p\to pJ/\ddot{I}ˆ\to p(\hat{I}{¼}^{+}\hat{I}{¼}^{-})$ by 007 and $γ^\ast~p\to p~J/ψ\to p~(e^+e^-)$ by CLAS12 allow us to extend the previous phenomenological determination of the J/\ensuremathψ-proton scattering length, $\hat{I}{\pm }_{J/\ddot{I}ˆp}$, using GlueX threshold data for ${\hat{I}}^{3}p\to pJ/\ddot{I}ˆ\to p(e^{+}{e}^{-})$. The agreement between all three J/\ensuremathψ data sets shows no indication of systematic differences between methodologies. Furthermore, perturbative QCD predictions support the phenomenological determination of heavy vector meson-nucleon scattering lengths. The role of the nucleon form factor, $F_N$, is discussed, and a possible correction to the phenomenological scattering length for heavy vector meson photoproduction is calculated using the pole form of $F_N$. Upcoming J-PARC threshold measurements of the reaction $\ddot{I}{€}^{-}p\to nJ/\ddot{I}ˆ\to n(l^{+}{l}^{-})$ will help to evaluate the possible role of heavy pentaquark, $P_c$, states in low-energy $J/\ddot{I}ˆ$ production and the effects caused by the nucleon form factors.

21 pages, 3 figures, 4 tables. Text was revised, including the nucleon form factor effect