Abstract
Inspired by the observation of the pentaquark states $P_{c}(4312),P_{c}(4440)$ and $P_{c}(4457)$ at LHCb, photoproduction of these three $P_{c}$ states via the interaction $\gamma p\rightarrow J/\psi p$ is investigated in an effective Lagrangian approach. The $t$-channel Pomeron exchange diffractive process is considered as the main background for the $J/\psi $ photoproduction. The numerical results show that the theoretical cross section, which is calculated by assuming a branching ratio $Br[P_{c}\rightarrow J/\psi p]\simeq 3\%$, is consistent with the existing experimental data of the $ \gamma p\rightarrow J/\psi p$ process. With such a branching ratio, if experimental precision reaches 0.1 nb within a bin of 100 MeV for photon energy, two peaks are expected to be obviously observed in the $J/\psi $ photoproduction. To observe the two-peak structure from $P_{c}(4440)$ and $ P_{c}(4457)$, higher precision, about 0.1nb/10 MeV, is required to distinguish two close pentaquarks. If the physical branching ratio is larger, the requirement of experimental precision will be reduced. The differential cross sections for reaction $\gamma p\rightarrow J/\psi p$ are also present. It is found that the $t$-channel Pomeron exchange provides a sharp increase at extreme forward angles and gives a sizable contribution at most energy points, while the contributions from the $s$-channel $P_{c}$ exchanges play important roles at threshold energies. The experimental measurement of the $\gamma p\rightarrow J/\psi p$ process in the near-threshold energy region around $E_{\gamma }\simeq 9.4-10.5$ GeV is suggested, and is accessible at CEBAF@JLab and COMPASS.
Highlights
As of many exotic hadrons have been observed and listed in the Review of Particle Physics (PDG) [1]
The numerical results show that the theoretical cross section, which is calculated by assuming a branching ratio Br1⁄2Pc → J=ψp ≃ 3%, is consistent with the existing experimental data of the γp → J=ψp process
The experimental data of the γp → J=ψp process seem to be quite consistent with the total cross section
Summary
Many exotic hadrons have been observed and listed in the Review of Particle Physics (PDG) [1]. An updated result was reported: three narrow pentaquark states, Pcð4312Þ; Pcð4440Þ, and Pcð4457Þ, were observed in the J=ψp invariant mass spectrum of the Λb → J=ψpK decays [3]. The existence of such molecular states is confirmed by the calculation in the constituent quark model with the meson-exchange mechanism at the quark level [6,8] Up to now, these hidden-charm pentaquarks were only observed in the Λb decay at LHCb. Production of the pentaquarks in other ways is very helpful to obtain the definite evidence for their nature as genuine states. The high-luminosity detectors at Jefferson Laboratory will produce highprecision data in future experiments One can expect these experiments to provide an opportunity to study the hiddencharm pentaquarks in photoproduction.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
