CMS-PAS-BPH-11-021

CMS-PAS-BPH-11-021
Measurement of the Prompt Double $\mathrm{J}/\psi$ Production Cross Section in pp Collisions at $\sqrt(s) =$ 7 TeV
CMS Collaboration
2013

Abstract: The cross section for the simultaneous production of two $\mathrm{J}/\psi$ mesons in proton-proton collisions at $\sqrt{s} =$ 7 TeV at the LHC from a sample corresponding to an integrated luminosity of 4.73 $\pm$ 0.12 fb $^{-1}$ has been measured with the CMS detector. The two $\mathrm{J}/\psi$ mesons are fully reconstructed via their decays into $\mu^+ \mu^-$ , and the signal yield is extracted with an extended maximum-likelihood fit. The acceptance region is defined by the individual $\mathrm{J}/\psi$ transverse momentum ( $p_\mathrm{T}^{\mathrm{J}/\psi}$ ) and rapidity ( $\|y^{\mathrm{J}/\psi}\|$ ): $p_\mathrm{T}^{\mathrm{J}/\psi}>$ 6.5 GeV/ $c$ for $\|y^{\mathrm{J}/\psi}\| <$ 1.2, $p_\mathrm{T}^{\mathrm{J}/\psi}>$ 6.5 $\rightarrow$ 4.5 GeV/ $c$ (where the $p_\mathrm{T}$ threshold scales linearly from 6.5 to 4.5 GeV/ $c$ ) in the region 1.2 $<\|y^{\mathrm{J}/\psi}\| <$ 1.43, and $p_\mathrm{T}^{\mathrm{J}/\psi}>$ 4.5 GeV/ $c$ for 1.43 $<\|y^{\mathrm{J}/\psi}\| <$ 2.2. The total cross section assuming unpolarized prompt double $\mathrm{J}/\psi$ production is found to be $\sigma =$ 1.49 $\pm$ 0.07 $\pm$ 0.14 nb, where the first uncertainty is statistical and the second is systematic. Different extreme assumptions about the $\mathrm{J}/\psi$ polarization can increase the cross section by as much as 27% or decrease it by as much as 31%. The differential cross section is measured in bins of the double $\mathrm{J}/\psi$ invariant mass, the absolute difference in rapidity of the two $\mathrm{J}/\psi$ mesons, and the transverse momentum of the double $\mathrm{J}/\psi$ system. The double $\mathrm{J}/\psi$ invariant mass distribution is examined for possible contributions from $\eta_b$ production.
Links: CDS record (PDF) ; inSPIRE record ; Public twiki page ; CADI line (restricted) ; Figures are available from the CDS record. These preliminary results are superseded in this paper, JHEP 09 (2014) 094.

Compact Muon Solenoid
LHC, CERN