Double polarization observables in pentaquark photoproduction

We investigate the properties of the hidden-charm pentaquark-like resonances first observed by the LHCb Collaboration in 2015, by measuring the polarization transfer KLL between the incident photon and the outgoing proton in the exclusive photoproduction of J=ψ near threshold. We present a first estimate of the sensitivity of this observable to the pentaquark photocouplings and hadronic branching ratios, and extend our predictions to the case of the initial-state helicity correlation ALL, using a polarized target. These results serve as a benchmark for the SBS experiment at Jefferson Lab, which proposes to measure for the first time the helicity correlations ALL and KLL in J=ψ exclusive photoproduction, in order to determine the pentaquark photocouplings and branching ratios.