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

Abstract

New threshold measurements for $γ~p\to p~J/ψ\to p~(μ^+μ^-)$ 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, $α_{J/ψp}$, using GlueX threshold data for $γ~p\to p~J/ψ\to p~(e^+e^-)$. 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. Upcoming J-PARC threshold measurements of the reaction $π^-~p\to n~J/ψ\to n~(l^+l^-)$ will help resolve a puzzle regarding the trend of the vector meson-nucleon scattering lengths, $|α_{Υp}| \ll |α_{J/ψp}| \ll |α_{φp}| \ll |α_{ωp}|$, which is consistent with the ``young vector meson'' hypothesis.

Figures (3)

• Figure 1: The total $\gamma~p \to J/\psi~p$ cross sections, $\sigma_t$, as a function of the J/$\psi$ CM momentum reported by the GlueX Collaboration (red filled circles) GlueX:2023pev (two points are filled in cyan at the dip around $q = 0.5 - 0.6~\mathrm{GeV/c}$ are discussed in the main text), the 007 Collaboration (shown in yellow-filled squares 007:2026dow), and the CLAS12 Collaboration (shown in blue-filled triangles) Chatagnon:2026qsv. The black dash-dotted curves represent polynomial fits to $\sigma_t$ using Eq. (\ref{['eq:eq3']}).
• Figure 2: The total threshold $\gamma~p \to V~p$ cross section, $\sigma_t$, derived from the A2 (magenta filled diamonds) Strakovsky:2014wja, CLAS12 (cyan filled squares) Strakovsky:2025ews, CLAS6 (blue filled circles) Strakovsky:2020uqs, and high-luminosity GlueX (red filled triangles) Strakovsky:2019bev data, and simulated EIC quasi-data Strakovsky:2021vyk based on the theoretical predictions of Ref. Guo:2021ibg (based at the Center for Nuclear Femtography) are shown as a function of the CM momentum $q$ of the final-state Vs. The vertical error bars represent the total uncertainties of the data, which sum statistical and systematic uncertainties in quadrature. Black dash-dotted curves show the fits of the data and quasi-data to a series of odd powers of $q$ using Eq. (\ref{['eq:eq3']}).
• Figure 3: Top: Comparison of $|\alpha_{V p}|$ estimated from threshold $V$ photoproduction on the proton target assuming VMD versus the inverse mass of the $V$s, i.e., $1/m_V$. Input data for phenomenological analyses came from A2 at MAMI (magenta filled diamond) Strakovsky:2014wja, ELPH (black open diamond) Ishikawa:2019rvz, and CBELSA/TAPS (black asterisk) Han:2022khg Collaborations for the $\omega$-meson case; CLAS6 (blue filled circle) Strakovsky:2020uqs and LEPS (black open circle) Han:2022khg Collaborations for the $\phi$-meson case; GlueX, 007, and CLAS12 (red filled triangle) Collaborations for the J/$\psi$-meson case; and theoretical predictions from the Center for Nuclear Femtography (yellow filled star) Strakovsky:2021vykGuo:2021ibg for the $\Upsilon$-meson case. The black dash-dotted line is a hypothetical fit to the data from Refs. Strakovsky:2014wjaStrakovsky:2020uqsStrakovsky:2021vyk with high-luminosity GlueX, 007, and CLAS12 for J/$\psi$p results using Eq. (\ref{['eq:eq5']}). Bottom: Uncertainties for individual SLs ($\Delta|\alpha_{V N}|~/~ |\alpha_{V N}|$).