Fraction of χc decays in prompt J/ψ production measured in pPb collisions at √sNN = 8.16 TeV

Abstract

[Abstract] The fraction of χc1 and χc2 decays in the prompt J/ψ yield, Fχc→J/ψ = σχc→J/ψ/σJ/ψ, is measured by the LHCb detector in pPb collisions at √sNN = 8.16 TeV. The study covers the forward (1.5 < y* < 4.0) and backward (−5.0 < y* < −2.5) rapidity regions, where y* is the J/ψ rapidity in the nucleon-nucleon center-of-mass system. Forward and backward rapidity samples correspond to integrated luminosities of 13.6 ± 0.3 and 20.8 ± 0.5 nb¯¹ , respectively. The result is presented as a function of the J/ψ transverse momentum pT,J/ψ in the range 1< pT,J/ψ < 20 GeV/c. The Fχc→J/ψ fraction at forward rapidity is compatible with the LHCb measurement performed in pp collisions at √s = 7TeV, whereas the result at backward rapidity is 2.4 σ larger than in the forward region for 1 < pT,J/ψ < 3 GeV/c. The increase of Fχc→J/ψ at low pT,J/ψ at backward rapidity is compatible with the suppression of the ψ(2S) contribution to the prompt J/ψ yield. The lack of in-medium dissociation of χc states observed in this study sets an upper limit of 180 MeV on the free energy available in these pPb collisions to dissociate or inhibit charmonium state formation.