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Links: CDS record (PDF) ; CADI line (restricted) ; These preliminary results are superseded in this paper, Submitted to PRD. The superseded preliminary plots can be found here.

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