CMS-PAS-BPH-14-008

CMS-PAS-BPH-14-008
Observation of $\Upsilon(1S)$ pair production at CMS
CMS Collaboration
May 2016

Abstract: The simultaneous production of two $\Upsilon(1S)$ mesons in proton-proton collisions is observed by CMS at $\sqrt s =$ 8 TeV at LHC in a data sample corresponding to an integrated luminosity of 20.7 fb $^{-1}$ . The statistical significance is well in excess of 5 standard deviations. Both $\Upsilon$ candidates are fully reconstructed via their decays into $\mu^{+}\mu^{-}$ . The acceptance region is defined by the individual $\Upsilon$ rapidity, $y(\Upsilon)$ , and transverse momentum, $p_{\mathrm{T}}(\Upsilon)$ : $\|y(\Upsilon)\| <$ 2.0 and $p_{\mathrm{T}}(\Upsilon)<$ 50 GeV. The total cross section for the production of $\Upsilon(1S)$ pairs assuming that both $\Upsilon(1S)$ mesons decay isotropically, is measured to be 68.8 $\pm$ 12.7 (stat) $\pm$ 7.4 (syst) $\pm$ 2.8 (BR) pb, where the third uncertainty results from the uncertainty in the $\Upsilon(1S) \rightarrow \mu^{+}\mu^{-}$ branching fraction. Different assumptions about the $\Upsilon(1S)$ polarization imply modifications to the cross section ranging from -38% to 36%.
Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ; These preliminary results are superseded in this paper, JHEP 05 (2017) 013. The superseded preliminary plots can be found here.

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Lego plot of $M^{(1)}_{\mu \mu }$ vs $M^{(2)}_{\mu \mu }$ .
png pdf	Figure 2-a: Projections of the 2D fit. (a) invariant mass of higher mass muon pairs, $M^{(1)}_{\mu \mu }$ . (b) invariant mass of lower mass muon pairs, $M^{(2)}_{\mu \mu }$ . The lower pads show the difference between the total fit curve and data, with red lines corresponding to a difference of $\pm$ 2 standard deviations.
png pdf	Figure 2-b: Projections of the 2D fit. (a) invariant mass of higher mass muon pairs, $M^{(1)}_{\mu \mu }$ . (b) invariant mass of lower mass muon pairs, $M^{(2)}_{\mu \mu }$ . The lower pads show the difference between the total fit curve and data, with red lines corresponding to a difference of $\pm$ 2 standard deviations.

Tables
png pdf	Table 1: Summary of relative systematic uncertainties in the $\Upsilon$ pair production cross section.
png pdf	Table 2: Relative change of acceptance corrected yield for different polarization assumptions.

Summary

The

$\Upsilon(1S)$ meson pair production where both

$\Upsilon(1S)$ mesons originate from the common vertex is observed with the CMS detector in proton-proton collisions at

$\sqrt s=$ 8 TeV at the LHC from a sample corresponding to an integrated luminosity of 20.7 fb

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

$\pm$ 7

$\Upsilon(1S)\Upsilon(1S)$ events is measured with the local significance, including systematics, that exceeds five standard deviations. Using the measured muon kinematics in the data, an event-based acceptance and efficiency correction method is applied, minimizing the model dependence of the cross section measurement. The total cross section of

$\Upsilon(1S)$ pair production measured within the single

$\Upsilon$ acceptance,

$|y(\Upsilon)|<$ 2.0 and

$p_{\mathrm{T}}(\Upsilon)<$ 50 GeV, is found to be

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

$\pm$ 12.7 (stat)

$\pm$ 7.4 (syst)

$\pm$ 2.8 (BR) pb, where the

$\Upsilon(1S)$ decay into muons is assumed to be isotropic. Different assumptions about the

$\Upsilon(1S)$ polarization imply modifications to the cross section ranging from -38% to 36%.

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