## Narrow Nucleon-$\psi(2S)$ Bound State and LHCb Pentaquarks

### Abstract

We interpret the newly discovered pentaquark $P_c(4450)$ as a bound state of charmonium $\psi(2S)$ and the nucleon. The binding potential is due to charmonium-nucleon interaction that in the heavy quark approximation is proportional to the product of the charmonium chromoelectric polarizability and the nucleon energy-momentum distribution. We use the large $N_c$ expansion to estimate the quarkonium polarizability and calculate the nucleon properties in the framework of the mean-field picture of light baryons. Two almost degenerate states $J^P=(1/2)^-$ and $J^P=(3/2)^-$ are predicted at the position of the $P_c(4450)$ pentaquark. We find that the nucleon-$\psi(2S)$ bound state has a naturally narrow width in the range of tens of MeV. The unitary multiplet partners of the $P_c(4450)$ pentaquark and the generalization to $b \bar b$-nucleon pentaquark bound states are discussed.Comment: 14 page

Topics: High Energy Physics - Phenomenology, High Energy Physics - Experiment, Nuclear Experiment
Publisher: 'American Physical Society (APS)'
Year: 2015
DOI identifier: 10.1103/PhysRevD.93.054039
OAI identifier: oai:arXiv.org:1512.00426

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