On LHCb pentaquarks as a baryon-psi(2S) bound state -- prediction of isospin 3/2 pentaquarks with hidden charm

Abstract

The pentaquark $P_c^+(4450)$ recently discovered by LHCb has been interpreted as a bound state of $Ψ(2S)$ and nucleon. The charmonium-nucleon interaction which provides the binding mechanism is given, in the heavy quark limit, in terms of charmonium chromoelectric polarizabilities and densities of the nucleon energy-momentum tensor (EMT). In this work we show in model-independent way, by exploring general properties of the effective interaction, that $Ψ(2S)$ can form bound states with nucleon and $Δ$. Using the Skyrme model to evaluate the effective interaction in the large-$N_c$ limit and estimate $1/N_c$ corrections, we confirm the results from prior work which were based on a different effective model (chiral quark soliton model). This shows that the interpretation of $P_c^+(4450)$ is remarkably robust and weakly dependent on the details of the effective theories for the nucleon EMT. We explore the formalism further and present robust predictions of isospin $\frac32$ bound states of $Ψ(2S)$ and $Δ$ with masses around $4.5\,{\rm GeV}$ and widths around $70\,{\rm MeV}$. The approach also predicts broader resonances in the $Ψ(2S)$-$Δ$ channel at $4.9\,{\rm GeV}$ with widths of the order of $150\,{\rm MeV}$. We discuss in which reactions these new isospin $\frac 32$ pentaquarks with hidden charm can be observed.