Compact Muon Solenoid
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| CMS-PAS-HIN-22-003 | ||
| Study of $ \chi_\mathrm{c} $ production in pPb collisions at $ \sqrt{\smash[b]{s_{\mathrm{NN}}}} = $ 8.16 TeV with the CMS experiment | ||
| CMS Collaboration | ||
| 28 April 2025 | ||
| Abstract: The production of prompt P-wave charmonium states $ \chi_\mathrm{c1} $(1P) and $ \chi_\mathrm{c2} $(2P) is studied in proton-lead (pPb) collisions at a center-of-mass energy per nucleon pair of $ \sqrt{\smash[b]{s_{\mathrm{NN}}}}= $ 8.16 TeV. The analysis is based on data with an integrated luminosity of 175 nb$ ^{-1} $ that were collected by CMS at the LHC. The $ \chi_\mathrm{c} $ states are measured via their decay $ \chi_\mathrm{c} \rightarrow \mathrm{J}\!/\!\psi \gamma $. The $ \mathrm{J}\!/\!\psi $ is then reconstructed through its decay to a muon pair, while the photon is reconstructed through its conversion to an electron-positron pair. The ratios of $ [\sigma (\chi_\mathrm{c1}) \times \mathrm{B}(\chi_\mathrm{c1} \rightarrow \mathrm{J}\!/\!\psi\gamma) + \sigma(\chi_\mathrm{c2})\times\mathrm{B}(\chi_\mathrm{c2} \rightarrow \mathrm{J}\!/\!\psi\gamma)] / \sigma(\mathrm{J}\!/\!\psi) $ and $ [\sigma (\chi_\mathrm{c2}) \times \mathrm{B}(\chi_\mathrm{c2} \rightarrow \mathrm{J}\!/\!\psi\gamma)] / [\sigma (\chi_\mathrm{c1}) \times \mathrm{B}(\chi_\mathrm{c1} \rightarrow \mathrm{J}\!/\!\psi\gamma)] $ are reported in the rapidity range $ |y(\mathrm{J}\!/\!\psi)| < $ 2.4 and in the transverse momentum range 6.5 $ < p_\mathrm{T}(\mathrm{J}\!/\!\psi) < $ 30 GeV. The $ \chi_\mathrm{c1} $-to-$ \mathrm{J}\!/\!\psi $ ratio is compatible with being constant as a function of rapidity and charged particle multiplicity in the event, and rises as a function of $ p_\mathrm{T} $. The $ \chi_\mathrm{c2} $-to-$ \chi_\mathrm{c1} $ ratio is flat versus charged multiplicity, rapidity, and $ p_\mathrm{T} $. Given that both ratios are consistent with the proton-proton (pp) results at similar energies, the findings rule out a strong additional suppression of the $ \chi_\mathrm{c} $ states relative to the $ \mathrm{J}\!/\!\psi $ states in pPb collisions. | ||
| Links: CDS record (PDF) ; CADI line (restricted) ; | ||
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Compact Muon Solenoid LHC, CERN |
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