Observation of pentaquark resonances in Λb → J/ψK−p decays

Abstract

LHCb has recently reported the observation of exotic structures in the J/ψp channel, in Λb → J/ψK−p decay, which we discuss here and refer to as charmoniumpentaquarkstates. The data sample corresponds to an integrated luminosity of 3.0 fb−1acquired with the LHCb detector from 7 and 8 TeV pp collisions. An amplitude analysisof the three-body final state reproduces the two-body mass and angular distributions. Toobtain a satisfactory fit of the structures seen in the J/ψp mass spectrum, it is necessaryto include two Breit-Wigner amplitudes that each describe a resonant state. Details aregiven on the significance, and prefered quantum numbers, of these two resonances.