CMS-SMP-17-006

CMS-SMP-17-006 ; CERN-EP-2017-177
Measurement of vector boson scattering and constraints on anomalous quartic couplings from events with four leptons and two jets in proton-proton collisions at $ \sqrt{s} = $ 13 TeV
CMS Collaboration
9 August 2017
Phys. Lett. B 774 (2017) 682
Abstract: A measurement of vector boson scattering and constraints on anomalous quartic gauge couplings from events with two Z bosons and two jets are presented. The analysis is based on a data sample of proton-proton collisions at $ \sqrt{s} = $ 13 TeV collected with the CMS detector and corresponding to an integrated luminosity of 35.9 fb$^{-1}$. The search is performed in the fully leptonic final state $\mathrm{ Z }\mathrm{ Z }\to\ell\ell\ell^{\prime}\!\ell^{\prime}\!$, where $\ell,\, \ell^{\prime}\! = \mathrm{ e }$ or $\mu$. The electroweak production of two Z bosons in association with two jets is measured with an observed (expected) significance of 2.7 (1.6) standard deviations. A fiducial cross section for the electroweak production is measured to be ${\sigma_{\textrm{EW}}(\mathrm{ p }\mathrm{ p }\rightarrow\mathrm{ Z }\mathrm{ Z }\textrm{jj}\rightarrow\ell\ell\ell^{\prime}\!\ell^{\prime}\textrm{jj}) } = $ 0.40$^{+0.21}_{-0.16}$ (stat) $^{+0.13}_{-0.09}$ (syst) fb, which is consistent with the standard model prediction. Limits on anomalous quartic gauge couplings are determined in terms of the effective field theory operators T0, T1, T2, T8, and T9. This is the first measurement of vector boson scattering in the ZZ channel at the LHC.
Links: e-print arXiv:1708.02812 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ;

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Representative Feynman diagrams for the EW- (top row and bottom left) and QCD-induced production (bottom right) of the $\mathrm{ Z } \mathrm{ Z } \textrm {jj}\rightarrow \ell \ell \ell ^{\prime }\!\ell ^{\prime } \textrm {jj}$ ($\ell , \ell ^{\prime }\!=\mathrm{ e } $ or $\mu $) final state. The scattering of massive gauge bosons as depicted in the top row is unitarized by the interference with amplitudes that feature the Higgs boson (bottom left).
png pdf	Figure 2: Distribution of the dijet pseudorapidity separation (left) and dijet invariant mass (right) for events passing the ZZjj selection, which requires $m_\textrm {jj} > $ 100 GeV. Points represent the data, filled histograms the expected signal and background contributions. No data beyond $ \|\Delta \eta _\textrm {jj}\|> $ 7 (left) and $m_\textrm {jj}> $ 1600 GeV (right) is observed.
png pdf	Figure 2-a: Distribution of the dijet pseudorapidity separation for events passing the ZZjj selection, which requires $m_\textrm {jj} > $ 100 GeV. Points represent the data, filled histograms the expected signal and background contributions. No data beyond $ \|\Delta \eta _\textrm {jj}\|> $ 7 is observed.
png pdf	Figure 2-b: Distribution of the dijet invariant mass for events passing the ZZjj selection, which requires $m_\textrm {jj} > $ 100 GeV. Points represent the data, filled histograms the expected signal and background contributions. No data beyond $m_\textrm {jj}> $ 1600 GeV is observed.
png pdf	Figure 3: Distribution of the BDT output in the control region obtained by selecting ZZjj events with $m_\textrm {jj}< $ 400 GeV or $ \|\Delta \eta _\textrm {jj}\| < $ 2.4 (left) and for the ZZjj selection (right). Points represent the data, filled histograms the expected signal and background contributions.
png pdf	Figure 3-a: Distribution of the BDT output in the control region obtained by selecting ZZjj events with $m_\textrm {jj}< $ 400 GeV or $ \|\Delta \eta _\textrm {jj}\| < $ 2.4. Points represent the data, filled histograms the expected signal and background contributions.
png pdf	Figure 3-b: Distribution of the BDT output for the ZZjj selection. Points represent the data, filled histograms the expected signal and background contributions.
png pdf	Figure 4: The $m_{\mathrm{ Z } \mathrm{ Z } }$ distribution in the ZZjj selection together with the SM prediction and two hypotheses for the aQGC coupling strengths. Points represent the data, filled histograms the expected signal and background contributions. The last bin includes all contributions with ${m_{\mathrm{ Z } \mathrm{ Z } } } > $ 1200 GeV.

Tables
png pdf	Table 1: Signal and background yields for the ZZjj selection together with the SM prediction and two hypotheses for the aQGC coupling strengths. Points represent the data, filled histograms the expected signal and background contributions. The last bin includes all contributions with ${m_{\mathrm{ Z } \mathrm{ Z } } } > $ 1200 GeV.
png pdf	Table 2: Expected and observed lower and upper 95% CL limits on the couplings of the quartic operators T0, T1, and T2, as well as the neutral current operators T8 and T9. The unitarity bounds are also listed. All coupling parameter limits are in TeV$^{-4}$, while the unitarity bounds are in TeV.

Summary

A search was performed for vector boson scattering in the four-lepton and two-jet final state using proton-proton collisions at 13 TeV. The data correspond to an integrated luminosity of 35.9 fb$^{-1}$ collected with the CMS detector at the LHC.

The electroweak production of two Z bosons in association with two jets was measured with an observed (expected) significance of 2.7 (1.6) standard deviations. The fiducial cross section is ${\sigma_{\textrm{EW}}(\mathrm{ p }\mathrm{ p }\rightarrow\textrm{ZZjj}\rightarrow\ell\ell\ell^{\prime}\!\ell^{\prime}\textrm{jj}) } = $ 0.40$^{+0.21}_{-0.16}$ (stat) $^{+0.13}_{-0.09}$ (syst) fb, consistent with the standard model prediction of 0.29 $^{+0.02}_{-0.03}$ fb.

Limits on anomalous quartic gauge couplings were set at the 95% confidence level in terms of effective field theory operators, in units of TeV$^{-4}$:

${-}0.46 < f_\textrm{T0}/\Lambda^4 <0.44$
${-}0.61 < f_\textrm{T1}/\Lambda^4 <0.61$
${-}1.2 < f_\textrm{T2}/\Lambda^4 < 1.2$
${-}0.84 < f_\textrm{T8}/\Lambda^4 <0.84$
${-}1.8 < f_\textrm{T9}/\Lambda^4 <1.8$.
These are the first results for the electroweak production of two Z bosons in association with jets at the LHC and the most stringent limits on the T0, T1, T2, T8, and T9 anomalous quartic gauge couplings to date.

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