CMS-PAS-SMP-15-012

CMS-PAS-SMP-15-012
Measurement of the differential cross sections for pairs of Z bosons produced in association with jets in pp collisions at $ \sqrt{s} = $ 8 TeV
CMS Collaboration
August 2016

Abstract: This note reports the measurement of the differential cross sections of two Z bosons produced in association with jets in pp collisions at a center-of-mass energy of $\sqrt{s}= $ 8 TeV. This analysis is based on a data sample collected with the CMS experiment at the LHC, corresponding to an integrated luminosity of 19.7 fb$^{-1}$. Measurements are performed in the leptonic decay modes $\mathrm{ZZ} \to \ell\ell\ell'\ell'$, where $\ell,\ell' = \mathrm{e}$, $\mu$.
Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ;

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1-a: Normalized differential cross sections of ${\mathrm{ Z } } {\mathrm{ Z } } \to 4\ell $ processes as a function of the multiplicity of jets (a) and central jets (b). Cross sections are compared to predictions from the MadGraph, Powheg and MadGraph5-aMCatNLO sets of samples. PYTHIA 6.4 is employed for all generators but MadGraph5-aMCatNLO, which uses PYTHIA 8.0. The total experimental uncertainties are shown with the hatched regions. Colored bands display the effect of varying the renormalization and factorization scales in Powheg and of varying the renormalization and factorization scales, PDFs and $\alpha _s$ in MadGraph5-aMCatNLO.
png pdf	Figure 1-b: Normalized differential cross sections of ${\mathrm{ Z } } {\mathrm{ Z } } \to 4\ell $ processes as a function of the multiplicity of jets (a) and central jets (b). Cross sections are compared to predictions from the MadGraph, Powheg and MadGraph5-aMCatNLO sets of samples. PYTHIA 6.4 is employed for all generators but MadGraph5-aMCatNLO, which uses PYTHIA 8.0. The total experimental uncertainties are shown with the hatched regions. Colored bands display the effect of varying the renormalization and factorization scales in Powheg and of varying the renormalization and factorization scales, PDFs and $\alpha _s$ in MadGraph5-aMCatNLO.
png pdf	Figure 2-a: Normalized differential cross sections of ${\mathrm{ Z } } {\mathrm{ Z } } \to 4\ell $ processes with $N_{jets}\ge 2$ as a function of the invariant mass of the two $ p_{\mathrm{T}}$-leading jets (a) and their interval in pseudorapidity (b). Cross sections are compared to predictions from the MadGraph, Powheg and MadGraph5-aMCatNLO sets of samples. PYTHIA 6.4 is employed for all generators but MadGraph5-aMCatNLO, which uses PYTHIA 8.0. The total experimental uncertainties are shown with the hatched regions. Colored bands display the effect of varying the renormalization and factorization scales in Powheg and of varying the renormalization and factorization scales, PDFs and $\alpha _s$ in MadGraph5-aMCatNLO.
png pdf	Figure 2-b: Normalized differential cross sections of ${\mathrm{ Z } } {\mathrm{ Z } } \to 4\ell $ processes with $N_{jets}\ge 2$ as a function of the invariant mass of the two $ p_{\mathrm{T}}$-leading jets (a) and their interval in pseudorapidity (b). Cross sections are compared to predictions from the MadGraph, Powheg and MadGraph5-aMCatNLO sets of samples. PYTHIA 6.4 is employed for all generators but MadGraph5-aMCatNLO, which uses PYTHIA 8.0. The total experimental uncertainties are shown with the hatched regions. Colored bands display the effect of varying the renormalization and factorization scales in Powheg and of varying the renormalization and factorization scales, PDFs and $\alpha _s$ in MadGraph5-aMCatNLO.
png pdf	Figure 3-a: Normalized differential cross sections of ${\mathrm{ Z } } {\mathrm{ Z } } \to 4\ell $ processes as a function of the $p_{\mathrm{T}}$-leading jet transverse momentum (a) and pseudorapidity (b), with $N_{jets}\ge 1$, and of the $p_{\mathrm{T}}$-sub-leading jet transverse momentum (c) and pseudorapidity (d), with $N_{jets}\ge 2$. Cross sections are compared to predictions from the MadGraph, Powheg and MadGraph5-aMCatNLO sets of samples. PYTHIA 6.4 is employed for all generators but MadGraph5-aMCatNLO, which uses PYTHIA 8.0. The total experimental uncertainties are shown with the hatched regions. Colored bands display the effect of varying the renormalization and factorization scales in Powheg and of varying the renormalization and factorization scales, PDFs and $\alpha _s$ in MadGraph5-aMCatNLO.
png pdf	Figure 3-b: Normalized differential cross sections of ${\mathrm{ Z } } {\mathrm{ Z } } \to 4\ell $ processes as a function of the $p_{\mathrm{T}}$-leading jet transverse momentum (a) and pseudorapidity (b), with $N_{jets}\ge 1$, and of the $p_{\mathrm{T}}$-sub-leading jet transverse momentum (c) and pseudorapidity (d), with $N_{jets}\ge 2$. Cross sections are compared to predictions from the MadGraph, Powheg and MadGraph5-aMCatNLO sets of samples. PYTHIA 6.4 is employed for all generators but MadGraph5-aMCatNLO, which uses PYTHIA 8.0. The total experimental uncertainties are shown with the hatched regions. Colored bands display the effect of varying the renormalization and factorization scales in Powheg and of varying the renormalization and factorization scales, PDFs and $\alpha _s$ in MadGraph5-aMCatNLO.
png pdf	Figure 3-c: Normalized differential cross sections of ${\mathrm{ Z } } {\mathrm{ Z } } \to 4\ell $ processes as a function of the $p_{\mathrm{T}}$-leading jet transverse momentum (a) and pseudorapidity (b), with $N_{jets}\ge 1$, and of the $p_{\mathrm{T}}$-sub-leading jet transverse momentum (c) and pseudorapidity (d), with $N_{jets}\ge 2$. Cross sections are compared to predictions from the MadGraph, Powheg and MadGraph5-aMCatNLO sets of samples. PYTHIA 6.4 is employed for all generators but MadGraph5-aMCatNLO, which uses PYTHIA 8.0. The total experimental uncertainties are shown with the hatched regions. Colored bands display the effect of varying the renormalization and factorization scales in Powheg and of varying the renormalization and factorization scales, PDFs and $\alpha _s$ in MadGraph5-aMCatNLO.
png pdf	Figure 3-d: Normalized differential cross sections of ${\mathrm{ Z } } {\mathrm{ Z } } \to 4\ell $ processes as a function of the $p_{\mathrm{T}}$-leading jet transverse momentum (a) and pseudorapidity (b), with $N_{jets}\ge 1$, and of the $p_{\mathrm{T}}$-sub-leading jet transverse momentum (c) and pseudorapidity (d), with $N_{jets}\ge 2$. Cross sections are compared to predictions from the MadGraph, Powheg and MadGraph5-aMCatNLO sets of samples. PYTHIA 6.4 is employed for all generators but MadGraph5-aMCatNLO, which uses PYTHIA 8.0. The total experimental uncertainties are shown with the hatched regions. Colored bands display the effect of varying the renormalization and factorization scales in Powheg and of varying the renormalization and factorization scales, PDFs and $\alpha _s$ in MadGraph5-aMCatNLO.

Tables

png pdf

Table 1:
The $ \mathrm{pp} \to {\mathrm{ Z } } {\mathrm{ Z } } \to \ell \ell \ell '\ell '$ production cross section as measured in each decay channel and for the sum of all channels in the fiducial region defined requiring: 60 $ < m_{{\mathrm{ Z } } } <$ 120 GeV for both Z bosons, leptons with $ p^e_{\mathrm{T}} >$ 7 GeV and $|\eta ^e| < $ 2.5 if electrons and $p^{\mu }_{\mathrm{T}} > $ 5 GeV and $|\eta ^{\mu }| < $ 2.4 if muons, at least one lepton with $p_{\mathrm{T}} > $ 20 GeV and another one with $p_{\mathrm{T}} > $ 10 GeV.

Summary

The differential cross section of Z boson pairs in association with jets produced in pp collisions at $ \sqrt{s} = $ 8 TeV has been measured in the leptonic decay channels pp $\to \mathrm{Z}\mathrm{Z}\to \ell\ell\ell'\ell'$ with $\ell,\ell'= \mathrm{e}$, $\mu$. The full 8 TeV data set is used corresponding to an integrated luminosity of 19.7 fb$^{-1}$. Simple sequential sets of lepton reconstruction, identification and isolation cuts and a set of kinematic cuts are used to obtain a clean sample of ZZ bosons decaying into a four-lepton final state accompanied by jets. The main backgrounds are estimated using data-driven techniques and Monte Carlo samples and are found to be very small with respect to the expected signal. The combined cross section is measured in the fiducial region defined by requiring the invariant mass of each Z boson between 60 and 120 GeV, leptons with $ p^{\mathrm{e}}_{\mathrm{T}} > $ 7 GeV and $|\eta^e| < $ 2.5 if electrons and $ p^{\mu}_{\mathrm{T}} >$ 5 GeV and $|\eta^{\mu}| < $ 2.4 if muons, at least one lepton with $ p_{\mathrm{T}} > $ 20 GeV and another one with $ p_{\mathrm{T}} > $ 10 GeV. It is: $\sigma_{\mathrm{p}\mathrm{p}\to \mathrm{Z}\mathrm{Z} \to 4\ell} =$ 20.4 $\pm$ 1.4 (stat) $^{+0.6}_{- 0.5}$ (syst) $\pm$ 0.5 (lumi) fb, in agreement with the SM prediction of 20.21$^{+0.67}_{-0.53}$ fb from [24]. Differential distributions for jet-related variables are presented and compared to three different sets of MC samples. In all three cases, the data/MC distribution of the jet multiplicity shows a decreasing trend, which is assumed to be due to higher order corrections to the ZZ production. The measured exclusive cross sections for $ \mathrm{pp} \to \mathrm{Z}\mathrm{Z} + n$ jets $\to \ell\ell\ell'\ell' + n$ jets for $n = 0$, $n = 1$, $n = 2$ and $n \ge 3$ ($|\eta^{jet}| <$ 4.7) are: $\sigma_{0 \mathrm{jet}}=$ 16.3 $\pm$ 1.2 (stat) $\pm$ 0.6 (syst) $\pm$ 0.4 (lumi) fb, $\sigma_{1 \mathrm{jet}}=$ 3.17 $\pm$ 0.62 (stat) $\pm$ 0.38 (syst) $\pm$ 0.08 (lumi) fb, $\sigma_{2 \mathrm{jet}}=$ 0.75 $\pm$ 0.32 (stat) $\pm$ 0.14 (syst) $\pm$ 0.02 (lumi) fb, $\sigma_{\ge3 \mathrm{jet}}=$ 0.135 $\pm$ 0.104 (stat) $\pm$ 0.045 (syst) $\pm$ 0.004 (lumi) fb. Distributions obtained by requiring more than one jet are consistent with their theoretical expectations.

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