### Speaker

### Description

A Pomeron-exchange model of the $\gamma p \to J/\psi p$ reaction has been used to make predictions for the on-going experiments at JLab. The parameters of the Pomeron-exchange amplitudes are determined by fitting the total cross section data of $\gamma p \to J/\psi p$ up to very high energy W = 300 GeV. To provide information for the search of nucleon resonances with hidden charm $N^*_{c\bar{c}}$, we then make predictions by including the resonant amplitude of $\gamma p \to N^*_{c\bar{c}} \to J/\psi p$ calculated from all available meson-baryons (MB) coupled-channel model of $N^*_{c\bar{c}}$ with MB = $\rho N$, $\omega N$, $J/\psi N$, $\bar{D}\Lambda_c$, $\bar{D}^* \Lambda_c$, $\bar{D}\Sigma_c$, $\bar{D}^*\Sigma_c$, $\bar{D}\Sigma^*_c$. The $N^*_{c\bar{c}}\to MB$ vertex interactions are determined from the partial width predicted from various theoretical models and SU(4) symmetry. The $\gamma p \to N^*_{c\bar{c}}$ is calculated from the Vector Meson Dominance (VMD) model as $\gamma p \to V p \to N^*_{c\bar{c}}$ with V = $\rho$, $\omega$, $J/\psi$. The model then depends on an off-shell form factor $\lambda^4/(\Lambda^4 + (q^2 - m^2_V)^2)$ which is needed to account for the $q^2$-dependence of VMD model.

It has been found that with $\Lambda = 0.55$ GeV, the predicted total cross sections are within the range of the very limited data in the energy region near $J/\psi$ production threshold. We then demonstrate that the $N^*_{c\bar{c}}$ can be most easily identified in the differential cross sections at large angles where the contribution from Pomeron-exchange becomes negligible.

Early Consideration | Yes |
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Graduate Student | No |