Study of the pentaquark states with a hidden charm in pp-collisions at LHC


Dzhelepov Laboratory of Nuclear Problems

Date and Time: Wednesday, 9 September 2020, at 11:00 AM

Venue: Online conference in Zoom

Seminar topic: “Study of the pentaquark states with a hidden charm in pp-collisions at LHC”

Speaker: Ivan Yeletskikh


In 2015, the LHCb experiment reported observation of two charged resonances, Pc(4380) and Pc(4450) in Λb baryons decays in the J/ψpK decay channel. Properties of these states implied they had a pentaquark structure with hidden charm. This discovery motivated a series of further theoretical and experimental studies. During 2016 – 2020, new results were obtained by different experiments: independent results on pentaquark signals were reported by ATLAS (no-signal hypothesis was excluded with the p−value=9⋅10−3), pentaquark signals were observed in proton-antiproton collisions at D0 with 3σ significance, a model-independent analysis was carried out and the contribution of pentaquarks to the Cabibbo-suppressed channel Λb → J/ψpπ was reported by LHCb. In 2019, LHCb discovered a new narrow state, Pc(4312). Moreover, Pc(4450) revealed a substructure, two narrow peaks of masses 4440 and 4457 MeV. Studies of these states are ongoing. The question remains open about the existence and properties of Pc(4380), with a large decay width ~200 MeV. No signals of pentaquarks in the photoproduction channel (γp → Pc) have been observed so far (experiment GlueX). Current studies include further analysis of Pc states, measuring their quantum numbers, performing their full amplitude analysis in different kinematic regions. No less interesting is observing new decay modes of pentaquarks — in particular to pairs of charmed hadrons. From QCD, it is natural to predict the existence of a spectrum of states: electrically neutral pentaquarks, pentaquarks with strangeness and beauty, etc. Future studies are to be dedicated to discovering them.

Record of the seminar by Ivan Yeletskikh,