First measurement of near-threshold J/$\psi$ exclusive photoproduction off the proton

The collaboration
Phys.Rev.Lett. 123 (2019) 072001, 2019.

Abstract
We report on the measurement of the $\gamma p \rightarrow J/\psi p$ cross section from $E_\gamma = 11.8$ GeV down to the threshold at $8.2$ GeV using a tagged photon beam with the GlueX experiment. We find the total cross section falls toward the threshold less steeply than expected from two-gluon exchange models. The differential cross section $d\sigma /dt$ has an exponential slope of $1.67 \pm 0.39$ GeV$^{-2}$ at $10.7$ GeV average energy. The LHCb pentaquark candidates $P_c^+$ can be produced in the $s$-channel of this reaction. We see no evidence for them and set model-dependent upper limits on their branching fractions $\mathcal{B}(P_c^+ \rightarrow J/\psi p)$ and cross sections $\sigma(\gamma p \to P_c^+)\times\mathcal{B}(P_c^+ \to J/\psi p)$.

• #### Total Cross Section

Data from Table 1 (Supplemental Material) and Figure 2

10.17182/hepdata.110173.v1/t1

$\gamma p \rightarrow J/\psi p$ total cross-sections, statistical and systematic errors of the individual points in bins of beam energy....

• #### Differential Cross Section

Data from Table 2 and Figure 1 (Supplemental Material)

10.17182/hepdata.110173.v1/t2

$\gamma p \rightarrow J/\psi p$ differential cross-sections, statistical and systematic errors of the individual points in bins of $-(t-t_{min})$. There...