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 K-LL between the incident photon and the outgoing proton in the exclusive photoproduction of J/psi 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 A(LL), 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 A(LL) and K-LL in J/psi exclusive photoproduction, in order to determine the pentaquark photocouplings and branching ratios.