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 Eletskikh

Abstract:

In 2015, the LHCb experiment reported observation of two charged resonances, P_c(4380) and P_c(4450) in Λ_b 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 Λ_b → J/ψpπ was reported by LHCb. In 2019, LHCb discovered a new narrow state, P_c(4312). Moreover, P_c(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 P_c(4380), with a large decay width ~200 MeV. No signals of pentaquarks in the photoproduction channel (γp → P_c) have been observed so far (experiment GlueX). Current studies include further analysis of P_c 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.

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