Towards clarifying the possibility of observation of the LHCb hidden-charm pentaquarks Pc+(4312), Pc+(4337), Pc+(4440) and Pc+(4457) in near-threshold charmonium photoproduction off protons and nuclei

We study the near-threshold J/psi meson photoproduction from protons and nuclei by considering incoherent direct non-resonant (gamma p -> J/psi p, gamma n -> J/psi n) and two-step resonant (gamma p -> Pci+-> J/psi p,gamma n -> Pci0 -> J/psi n, i = 1, 2, 3, 4; P+,0 c1 = Pc+,0(4312), Pc2+,0 = Pc+,0(4337), Pc3+,0 = P +,0 c (4440), c (4457)) charmonium production processes. We calculate the absolute excitation functions, energy and momentum distributions for the non-resonant, resonant and for the combined (non-resonant plus resonant) production of J/psi mesons on protons as well as, using the nuclear spectral function approach, on carbon and tungsten target nuclei at near-threshold incident photon energies by assuming the spin-parity assignments of the hidden-charm resonances P+,0 c(4312), Pc+,0 (4337), Pc+,0(4440) and P+,0 c (4457) as JP = (1/2)-, JP = (1/2)-, JP = (1/2)- and JP = (3/2)- within three different realistic scenarios for the branching ratios of their decays to the J/psi p and J/psi n modes (0.25, 0.5 and 1%). We show that will be very hard to measure the P ci+ pentaquark states through the scan of the J/psi total photoproduction cross section on a proton target in the near-threshold energy region around the resonant photon energies of 9.44, 9.554, 10.04 and 10.12 GeV if these branching ratios similar to 1% and less. We also demonstrate that at these photon beam energies the J/psi energy and momentum combined distributions considered reveal distinct sensitivity to the above scenarios, respectively, at low J/psi total energies and momenta, which implies that they may be an important tool to provide further evidence for the existence of the pentaquark P ci+ and Pci0 resonances and to get valuable information on their decay rates to the J/psi p and J/psi n final states. The measurements of these distributions could be performed in the future at the 12 GeV CEBAF facility.

Automated summary

In this study, we investigate the near-threshold J/psi meson photoproduction from protons and nuclei. We consider both direct non-resonant and two-step resonant production processes. Our calculations show that the measurement of the P ci+ pentaquark states will be challenging, but the combined energy and momentum distributions of J/psi mesons can provide valuable information for confirming the existence of these resonances.