CMS-PAS-HIN-23-013

CMS-PAS-HIN-23-013
Observation of double-J/$\psi$ meson production in pPb collisions at 8.16 TeV
CMS Collaboration
27 February 2024

Abstract: The first observation of the concurrent production of two J/$\psi$ mesons in proton-nucleus collisions is presented. The analysis is based on a data sample recorded at a nucleon-nucleon center-of-mass energy of 8.16 TeV by the CMS experiment at the CERN LHC corresponding to an integrated luminosity of 174.6 nb$^{-1} $. The two J/$\psi$ mesons are reconstructed in their $ \mu^+\mu^- $ decay channel for transverse momenta $ p_{\mathrm{T}} > $ 6.5 GeV and rapidity $ \|y\| < $ 2.4. Events where the second J/$\psi$ meson is reconstructed in the dielectron channel are also considered in the search. The $ \mathrm{pPb}\to\mathrm{J}/\psi\mathrm{J}/\psi+\mathrm{X} $ process is observed with a significance of 5.3 standard deviations. The measured inclusive fiducial cross section, using the four-muon channel alone, is $ \sigma(\mathrm{pPb}\to\mathrm{J}/\psi\mathrm{J}/\psi+\mathrm{X})= $ 22.0 $ \pm $ 8.9 $ $ (stat) $ \pm 1.5 $ (syst) nb. This result is compared to theoretical perturbative quantum chromodynamics predictions at next-to-leading-order accuracy, including nuclear parton distribution functions, for the production of two J/$\psi$ mesons in single- (SPS) and double- (DPS) parton scatterings. A fit of the data to the expected SPS and DPS kinematic distributions of the two J/$\psi$ mesons yields, $ \sigma^{\mathrm{pPb}\to\mathrm{J}/\psi\mathrm{J}/\psi+\mathrm{X}}_\text{SPS}= $ 16.5 $ \pm $ 10.8 $ $ (stat) $ \pm 0.1 $ (syst) nb and $ \sigma^{\mathrm{pPb}\to\mathrm{J}/\psi\mathrm{J}/\psi+\mathrm{X}}_\text{DPS}= $ 5.4 $ \pm $ 6.2 $ $ (stat) $ \pm 0.4 $ (syst) nb, respectively. This latter result can be transformed into an upper limit on the effective DPS cross section, which characterizes the area occupied by the interacting partons in the transverse space, of $ \sigma_\text{eff} > $ 1.0 mb at 95% confidence level.
Links: CDS record (PDF) ; CADI line (restricted) ; These preliminary results are superseded in this paper, Submitted to PRD. The superseded preliminary plots can be found here.

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