Deciphering the mechanism of near-threshold $J/\psi$ photoproduction

Abstract

The photoproduction of the $J/\psi$ off the proton is believed to deepen our understanding of various physics issues. On the one hand, it is proposed to provide access to the origin of the proton mass, based on the QCD multipole expansion. On the other hand, it can be employed in a study of pentaquark states. The process is usually assumed to proceed through vector-meson dominance, that is the photon couples to a $J/\psi$ which rescatters with the proton to give the $J/\psi p$ final state. In this Letter, we provide a compelling hint for and propose measurements necessary to confirm a novel production mechanism via the ${\Lambda }_c{\bar{D}}^{(\ast )}$ intermediate states. In particular, there must be cusp structures at the ${\Lambda }_c{\bar{D}}^{(\ast )}$ thresholds in the energy dependence of the $J/\psi$ photoproduction cross section. The same mechanism also implies the $J/\psi$-nucleon scattering lengths of order 1 mfm. Given this, one expects only a minor contribution of charm quarks to the nucleon mass.

6 pages, 5 figures

References in corpus (9)

• Multiquark Resonances
• Pentaquark and Tetraquark states
• Effect of charmed meson loops on charmonium transitions
• Studying the P_c(4450) resonance in J/psi photoproduction off protons
• Possibility to study pentaquark states $P_c(4312),P_c(4440)$, and $P_c(4457)$ in $\gamma p\to J/\psi p$ reaction
• Accessing the real part of the forward $J/\psi$-p scattering amplitude from $J/\psi$ photo-production on protons around threshold
• ${\rm Y}$ photo-production on the proton at the Electron-Ion Collider
• J/psi absorption by nucleons in the meson-exchange model
• Identify the hidden charm pentaquark signal from non-resonant background in electron-proton scattering

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