Near-Threshold OPE Constraints and High-Energy Diffractive Dynamics in J/psi Photoproduction

Abstract

We analyze direct-proton forward-intercept data in the resolved near-threshold region of exclusive $J/\ddot{I}ˆ$ photoproduction and elastic total cross sections at HERA. The threshold calculation uses the leading-twist Coulombic OPE with the exact physical-domain target-mass resummation and a Peskin-consistent modern-PDF convolution. After an overall normalization and a subtraction constant are fitted, the six GlueX and CLAS12 intercepts are compatible with the OPE-generated energy dependence, but the exact-TMC and no-TMC fits differ by only $\hat{I}”\ddot{I}{‡}^2=0.021$. A two-parameter empirical exponential gives an equally good description, and $C_{\mathrm{sub}}=0$ increases the profiled minimum by only $0.033$. Thus current data identify a threshold curve, not the target-mass correction or subtraction constant separately. Propagation of 255 PDF members gives a conditional internal PDF uncertainty below $0.9\%$, while the Coulombic binding scale dominates the tested model dependence. Independently, a fit using the published H1 systematic decomposition and a reconstructed ZEUS covariance model gives $N_{90}=76.6\pm 2.3$~nb and $\hat{I}´=0.695\pm 0.023$. The absence of selected direct-proton data between $W\simeq 4.73$ and $20$~GeV prevents any data-driven determination of the location, width, or phase evolution of the crossover to high-energy diffraction.

17 pages, 6 figures

Topics & keywords

References in corpus (3)

• The energy dependence of exclusive heavy vector meson photoproduction cross-sections and NLO BFKL evolution
• Measurement of the near-threshold J$/\ddot{I}ˆ$ photoproduction cross section with the CLAS12 experiment
• Target-Mass Corrections in the OPE Sum-Rule Approach to Quarkonium-Nucleon Interactions with Global-Fit PDFs: an $x$-Resolved Analysis