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| CMS-SMP-14-014 ; CERN-EP-2016-205 | ||
| Measurement of the WZ production cross section in pp collisions at $\sqrt{s} = $ 7 and 8 TeV and search for anomalous triple gauge couplings at $ \sqrt{s} = $ 8 TeV | ||
| CMS Collaboration | ||
| 19 September 2016 | ||
| Eur. Phys. J. C 77 (2017) 236 | ||
| Abstract: The WZ production cross section is measured by the CMS experiment at the CERN LHC in proton-proton collision data samples corresponding to integrated luminosities of 4.9 fb$^{-1}$ collected at $ \sqrt{s} = $ 7 TeV, and 19.6 fb$^{-1}$ at $ \sqrt{s} = $ 8 TeV. The measurements are performed using the fully-leptonic WZ decay modes with electrons and muons in the final state. The measured cross sections for 71 $ < m_{\mathrm{ Z }} < $ 111 GeV are $\sigma(\mathrm{ p }\mathrm{ p }\to\mathrm{ W }\mathrm{ Z };\ \sqrt{s} = 7\, \mathrm{TeV}) =$ 20.14 $\pm$ 1.32 (stat) $\pm$ 1.13 (syst) $\pm$ 0.44 (lumi) pb and $\sigma(\mathrm{ p }\mathrm{ p }\to\mathrm{ W }\mathrm{ Z };\ \sqrt{s} = 8\, \mathrm{TeV}) =$ 24.09 $\pm$ 0.87 (stat) $\pm$ 1.62 (syst) $\pm$ 0.63 (lumi) pb. Differential cross sections with respect to the Z boson p$_{\mathrm{T}}$, the leading jet $p_{\mathrm{T}}$, and the number of jets are obtained using the $\sqrt{s} =$ 8 TeV data. The results are consistent with standard model predictions and constraints on anomalous triple gauge couplings are obtained. | ||
| Links: e-print arXiv:1609.05721 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; | ||
| Figures & Tables | Summary | Additional Tables | References | CMS Publications |
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| Figures | |
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Figure 1:
Leading-order Feynman diagrams for WZ production in proton-proton collisions. The three diagrams represent contributions from (left) $s$-channel through TGC, (middle) $t$-channel, and (right) $u$-channel. |
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Figure 1-a:
Leading-order Feynman diagram for WZ production in proton-proton collisions. The diagram represents the contribution from $s$-channel through TGC. |
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Figure 1-b:
Leading-order Feynman diagram for WZ production in proton-proton collisions. The diagram represents the contribution from $t$-channel. |
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Figure 1-c:
Leading-order Feynman diagram for WZ production in proton-proton collisions. The diagram represents the contribution from $u$-channel. |
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Figure 2:
Distributions of the dilepton invariant mass $m_{\ell \ell }$ in the WZ candidate events in 7 TeV (left) and 8 TeV (right) data. Points represent data and the shaded histograms represent the WZ signal and the background processes. The contribution from non-prompt leptons, dominated by the ${\mathrm{ t } {}\mathrm{ \bar{t} } }$ and Z+jets production, is obtained from data control samples. The contribution from all other backgrounds, labeled `MC background', as well as the signal contribution are determined from simulation. |
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Figure 2-a:
Distributions of the dilepton invariant mass $m_{\ell \ell }$ in the WZ candidate events in 7 TeV data. Points represent data and the shaded histograms represent the WZ signal and the background processes. The contribution from non-prompt leptons, dominated by the ${\mathrm{ t } {}\mathrm{ \bar{t} } }$ and Z+jets production, is obtained from data control samples. The contribution from all other backgrounds, labeled `MC background', as well as the signal contribution are determined from simulation. |
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Figure 2-b:
Distributions of the dilepton invariant mass $m_{\ell \ell }$ in the WZ candidate events in 8 TeV data. Points represent data and the shaded histograms represent the WZ signal and the background processes. The contribution from non-prompt leptons, dominated by the ${\mathrm{ t } {}\mathrm{ \bar{t} } }$ and Z+jets production, is obtained from data control samples. The contribution from all other backgrounds, labeled `MC background', as well as the signal contribution are determined from simulation. |
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Figure 3:
Ratio of measured inclusive cross sections to NNLO predictions. The vertical gray bands represent the theoretical uncertainties at 7 and 8 TeV. |
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Figure 4:
The WZ total cross section as a function of the proton-proton centre-of-mass energy. Results from the CMS and ATLAS experiments are compared to the predictions of MCFM and Matrix. The data uncertainties are statistical (inner bars) and statistical plus systematic added in quadrature (outer bars). The band around the theoretical predictions reflects uncertainties generated by varying the factorization and renormalization scales up and down by a factor of two and also the (PDF+$\alpha _S$) uncertainty of NNPDF3.0 for NLO predictions. The theoretical predictions and the CMS 13 TeV cross section are calculated for the Z boson mass window 60-120 GeV. The CMS 7 and 8 TeV cross sections presented in this paper are calculated for the Z boson mass window 71-111 GeV (estimated correction factor 2%), while all ATLAS measurements are performed with the Z boson mass window 66-116 GeV (1%). |
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Figure 5:
Differential WZ cross section at $ \sqrt{s} = $ 8 TeV as a function of the Z boson transverse momentum. The measurement is compared with MCFM and MadGraph predictions. The MadGraph prediction is rescaled to the total NLO cross section as predicted by MCFM . The error bands in the ratio plots indicate the relative errors on the data in each bin and contain both statistical and systematic uncertainties. |
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Figure 6:
Differential WZ cross section at $ \sqrt{s} = $ 8 TeV as a function of: (left) the leading jet transverse momentum; (right) the number of accompanying jets. The measurements are compared with MadGraph predictions. The MadGraph prediction is rescaled to the total NLO cross section as predicted by MCFM . The error bands in the ratio plots indicate the relative errors on the data in each bin and contain both statistical and systematic uncertainties. |
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Figure 6-a:
Differential WZ cross section at $ \sqrt{s} = $ 8 TeV as a function of the leading jet transverse momentum. The measurements are compared with MadGraph predictions. The MadGraph prediction is rescaled to the total NLO cross section as predicted by MCFM . The error bands in the ratio plots indicate the relative errors on the data in each bin and contain both statistical and systematic uncertainties. |
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Figure 6-b:
Differential WZ cross section at $ \sqrt{s} = $ 8 TeV as a function of the number of accompanying jets. The measurements are compared with MadGraph predictions. The MadGraph prediction is rescaled to the total NLO cross section as predicted by MCFM . The error bands in the ratio plots indicate the relative errors on the data in each bin and contain both statistical and systematic uncertainties. |
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Figure 7:
Transverse momentum distribution of the Z boson candidates, in linear scale (left) and log scale (right) for all channels combined. The SM WZ contribution (light orange) is normalized to the predicted cross section from MCFM . Dashed lines correspond to aTGC expectations with different parameter values. The last bin includes the integral of the tail. |
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Figure 7-a:
Transverse momentum distribution of the Z boson candidates, in linear scale for all channels combined. The SM WZ contribution (light orange) is normalized to the predicted cross section from MCFM . Dashed lines correspond to aTGC expectations with different parameter values. The last bin includes the integral of the tail. |
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Figure 7-b:
Transverse momentum distribution of the Z boson candidates, in log scale for all channels combined. The SM WZ contribution (light orange) is normalized to the predicted cross section from MCFM . Dashed lines correspond to aTGC expectations with different parameter values. The last bin includes the integral of the tail. |
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Figure 8:
Two-dimensional observed 95% CL limits and expected 68%, 95% and 99% CL limits on anomalous coupling parameters $\Delta \kappa ^{{\mathrm{ Z } } }$ and $\Delta g_{1}^{{\mathrm{ Z } } }$. |
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Figure 9:
Two-dimensional observed 95% CL limits and expected 68%, 95% and 99% CL limits on anomalous coupling parameters $\Delta g_{1}^{{\mathrm{ Z } } }$ and $\lambda ^{{\mathrm{ Z } } }$. |
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Figure 10:
Two-dimensional observed 95% CL limits and expected 68%, 95% and 99% CL limits on anomalous coupling parameters $\Delta \kappa ^{{\mathrm{ Z } } }$ and $\lambda ^{{\mathrm{ Z } } }$. |
| Tables | |
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Table 1:
Expected and observed event yields at $\sqrt {s} = $ 7 and 8 TeV . The contributions from ${\mathrm{ t } {}\mathrm{ \bar{t} } } $, Z+jets, and other processes with non-prompt leptons have been determined from data control samples, as described in the text. Backgrounds with at least three bosons in the decay chain comprised of WZZ, ZZZ, WWZ, WWW, ${\mathrm{ t } {}\mathrm{ \bar{t} } } \mathrm{ W } $, ${\mathrm{ t } {}\mathrm{ \bar{t} } } {\mathrm{ Z } } $, ${\mathrm{ t } {}\mathrm{ \bar{t} } } \mathrm{ W } \mathrm{ W } $, ${\mathrm{ t } {}\mathrm{ \bar{t} } } \gamma $ and $\mathrm{ W } \mathrm{ W } \gamma $ events, are referred to as VVV. Combined statistical and systematic uncertainties are shown, except for the WZ signal where only statistical uncertainties are shown. |
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Table 2:
Summary of relative uncertainties, in units of percent, in the WZ cross section measurement at 7 and 8 TeV . |
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Table 3:
Measured WZ cross section in the four leptonic channels at $\sqrt {s} = $ 7 and 8 TeV . |
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Table 4:
Differential WZ cross section as a function of the Z transverse momentum at $ \sqrt{s} = $ 8 TeV for the four leptonic final states. The first uncertainty is statistical, the second is systematic, and the third is the integrated luminosity. |
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Table 5:
Differential WZ cross section as a function of the jet multiplicity at $ \sqrt{s} = $ 8 TeV for the four leptonic final states. Notations are as in Table 4. |
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Table 6:
Differential WZ cross section as a function of the leading jet transverse momentum at $ \sqrt{s} = $ 8 TeV for the four leptonic final states. Notations are as in Table 4. |
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Table 7:
Combined result for the differential WZ cross sections at $ \sqrt{s} = $ 8 TeV. |
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Table 8:
One-dimensional limits on the aTGC parameters at a 95% CL for $\mathrm{ W } {\mathrm{ Z } } \to \ell \nu \ell '\ell '$. |
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Table 9:
One-dimensional limits on the EFT parameters at a 95% CL for ${\mathrm{ W } {\mathrm{ Z } } }\to \ell \nu \ell '\ell '$. |
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Table 10:
Lowest incoming partons energy for which observed limits on the coefficients would lead to unitarity violation. |
| Summary |
| This paper reports measurements of the WZ inclusive cross section in proton-proton collisions at $\sqrt{s} = $ 7 and 8 TeV in the fully-leptonic WZ decay modes with electrons and muons in the final state. The data samples correspond to integrated luminosities of 4.9 fb$^{-1}$ for the 7 TeV measurement and 19.6 fb$^{-1}$ for the 8 TeV measurement. The measured production cross sections for 71 $ < m_{\mathrm{ Z }} < $ 111 GeV are $\sigma(\mathrm{ p }\mathrm{ p }\to\mathrm{ W }\mathrm{ Z };\ \sqrt{s} = 7\, \mathrm{TeV}) =$ 20.14 $\pm$ 1.32 (stat) $\pm$ 1.13 (syst) $\pm$ 0.44 (lumi) pb and $\sigma(\mathrm{ p }\mathrm{ p }\to\mathrm{ W }\mathrm{ Z };\ \sqrt{s} = 8\, \mathrm{TeV}) =$ 24.09 $\pm$ 0.87 (stat) $\pm$ 1.62 (syst) $\pm$ 0.63 (lumi) pb. These results are consistent with standard model predictions. Using the data collected at $ \sqrt{s} = $ 8 TeV, results on differential cross sections are also presented, and a search for anomalous WWZ couplings has been performed. The following one-dimensional limits at 95% CL are obtained: $-0.21 < \Delta\kappa^{\mathrm{ Z }} < 0.25$, $-0.018 < \Delta g_{1}^{\mathrm{ Z }} < 0.035$, and $-0.018 < \lambda^{\mathrm{ Z }} < 0.016$. |
| Additional Tables | |
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Additional Table 1:
Expected and observed event yields at $ \sqrt{s} = $ 8 TeV as a function of the number of observed jets. The contributions from ${\mathrm{ t } {}\mathrm{ \bar{t} } } $, Z+jets, and other processes with nonprompt leptons have been determined from data control samples, as described in the publication. Backgrounds with at least three bosons in the decay chain comprised of WZZ, ZZZ, WWZ, WWW, ${\mathrm{ t } {}\mathrm{ \bar{t} } }$W, ${\mathrm{ t } {}\mathrm{ \bar{t} } } $Z, ${\mathrm{ t } {}\mathrm{ \bar{t} } } $WW, ${\mathrm{ t } {}\mathrm{ \bar{t} } } \gamma $ and WW$\gamma $ events, are referred to as VVV. Combined statistical and systematic uncertainties are shown, except for the WZ signal where only statistical uncertainties are shown. |
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