Mass spectra of hidden-charm molecular pentaquarks states

Very recently, the LHCb Collaboration has reported two hidden-charmed resonances P_c(4380) and P_c(4450) consistent with pentaquark states in the Λ_b⁰ → K^-J/Ψp process with masses (widths) (4380 ±8 ± 29) MeV ((205 ±18 ± 86) MeV) and (4449.8 ±1.7 ± 2.5) MeV ((39 ±5 ±19) MeV), respectively. The observation of the P_c states has aroused the theorist's strong interest in the hidden-charm pentaquark states. They have been studied in various frameworks, such as the molecule-like pentaquark states, the diquark-diquark-antiquark type pentaquark states, the diquark-triquark type pentaquark states, re-scattering effects, etc. An identification of pentaquark states as exotic hadron has been one of the long standing problems in the physics of strong interaction and quantum chromodynamics (QCD). A decade ago lots of discussion were made about pentaquarks states but due to lack of further experimental evidences the study of pentaquarks have been almost gone in the darkness. But, recent remarkable observation of two resonances i.e. P_c(4380) and P_c(4450) with hidden charm and the minimal quark content cc-baruud provided new impact for studies of pentaquark states and opens a new window to study the exotic hadronic matter