CMS-BPH-14-008

CMS-BPH-14-008 ; CERN-EP-2016-237
Observation of $\Upsilon(\mathrm{1S})$ pair production in proton-proton collisions at $\sqrt{s} =$ 8 TeV
CMS Collaboration
23 October 2016
JHEP 05 (2017) 013
Abstract: Pair production of $\Upsilon(\mathrm{1S})$ mesons is observed at the LHC in proton-proton collisions at $\sqrt{s} =$ 8 TeV by the CMS experiment in a data sample corresponding to an integrated luminosity of 20.7 fb $^{-1}$ . Both $\Upsilon(\mathrm{1S})$ candidates are fully reconstructed via their decays to $\mu^{+}\mu^{- }$ . The fiducial acceptance region is defined by an absolute $\Upsilon(\mathrm{1S})$ rapidity smaller than 2.0. The fiducial cross section for the production of $\Upsilon(\mathrm{1S})$ pairs, assuming that both mesons decay isotropically, is measured to be 68.8 $\pm$ 12.7 (stat) $\pm$ 7.4 (syst) $\pm$ 2.8 ( $\mathcal{B}$ ) pb, where the third uncertainty comes from the uncertainty in the branching fraction of $\Upsilon(\mathrm{1S})$ decays to $\mu^{+}\mu^{-}$ . Assuming instead that the $\Upsilon(\mathrm{1S})$ mesons are produced with different polarizations leads to variations in the measured cross section in the range from $-38$ % to $+36$ %.
Links: e-print arXiv:1610.07095 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; CADI line (restricted) ;

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Two-dimensional distribution of $M^{(1)}_{\mu \mu }$ vs. $M^{(2)}_{\mu \mu }$ .
png pdf	Figure 2: Invariant mass distributions of the higher-mass muon pair (left) and the lower-mass muon pair (right). The data are shown by the points. The different curves show the contributions of the various event categories from the fit.
png pdf	Figure 2-a: Invariant mass distribution of the higher-mass muon pair. The data are shown by the points. The different curves show the contributions of the various event categories from the fit.
png pdf	Figure 2-b: Invariant mass distribution of the lower-mass muon pair. The data are shown by the points. The different curves show the contributions of the various event categories from the fit.

Tables
png pdf	Table 1: Summary of the relative systematic uncertainties in the $\Upsilon(\mathrm{1S})$ pair production cross section.
png pdf	Table 2: Relative change in percent of the acceptance-corrected $\Upsilon(\mathrm{1S})\Upsilon(\mathrm{1S})$ yield for different polarization assumptions with respect to that for $\lambda _{\theta 1} = \lambda _{\theta 2} =$ 0.

Summary

The first observation of

$\Upsilon(\mathrm{1S})$ pair production has been performed with the CMS detector in proton-proton collisions at

$\sqrt{s} =$ 8 TeV from a sample corresponding to an integrated luminosity of 20.7 fb

$^{-1}$ . A signal yield of 38

$\pm$ 7

$\Upsilon(\mathrm{1S})\Upsilon(\mathrm{1S})$ events is measured with a significance exceeding five standard deviations. Using the measured muon kinematic properties in the data, an event-based acceptance and efficiency-correction method is applied, minimizing the model dependence of the cross section measurement. The fiducial cross section of

$\Upsilon(\mathrm{1S})$ pair production measured within the single-

$\Upsilon$ acceptance

$|y^{\Upsilon}|<2.0$ is found to be

$\sigma_{\mathrm{fid}} =$ 68.8

$\pm$ 12.7 (stat)

$\pm$ 7.4 (syst)

$\pm$ 2.8 (

$\mathcal{B}$ ) pb, where the

$\Upsilon(\mathrm{1S})$ decay into muons is assumed to be isotropic. Assuming instead that the

$\Upsilon(\mathrm{1S})$ mesons are produced with different polarizations leads to variations in the measured cross section in the range from

$-$ 38% to

$+$ 36%. An effective cross section is also estimated using our result that is in agreement with the values from heavy-quarkonium measurements, but is smaller than that from multijet studies.

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