Fraction of χ_c Decays in Prompt J/ψ Production Measured in pPb Collisions at √s_NN = 8.16 TeV

The fraction of 𝜒_𝑐⁢1 and 𝜒_𝑐⁢2 decays in the prompt 𝐽/𝜓 yield, 𝐹_{𝜒𝑐→𝐽/𝜓=𝜎𝜒𝑐→𝐽/𝜓/𝜎𝐽/𝜓}, is measured by the LHCb detector in 𝑝⁢Pb collisions at √𝑠_NN=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 𝐹_{𝜒𝑐→𝐽/𝜓} fraction at forward rapidity is compatible with the LHCb measurement performed in 𝑝⁢𝑝 collisions at √𝑠=7  TeV, 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⁡(2⁢𝑆) contribution to the prompt 𝐽/𝜓 yield. The lack of in-medium dissociation of 𝜒_𝑐 states observed in this study sets an upper limit of 180 MeV on the free energy available in these 𝑝⁢Pb collisions to dissociate or inhibit charmonium state formation.