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| CMS-SMP-18-001 ; CERN-EP-2018-333 | ||
| Measurement of electroweak WZ boson production and search for new physics in WZ + two jets events in pp collisions at $\sqrt{s} = $ 13 TeV | ||
| CMS Collaboration | ||
| 14 January 2019 | ||
| Phys. Lett. B 795 (2019) 281 | ||
| Abstract: A measurement of WZ electroweak (EW) vector boson scattering is presented. The measurement is performed in the leptonic decay modes $\mathrm{W}\mathrm{Z} \to \ell\nu\ell'\ell'$, where $\ell, \ell' = $ e, $\mu$. The analysis is based on a data sample of proton-proton collisions at $\sqrt{s} = $ 13 TeV at the LHC collected with the CMS detector and corresponding to an integrated luminosity of 35.9 fb$^{-1}$. The WZ plus two jet production cross section is measured in fiducial regions with enhanced contributions from EW production and found to be consistent with standard model predictions. The EW WZ production in association with two jets is measured with an observed (expected) significance of 2.2 (2.5) standard deviations. Constraints on charged Higgs boson production and on anomalous quartic gauge couplings in terms of dimension-eight effective field theory operators are also presented. | ||
| Links: e-print arXiv:1901.04060 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Representative Feynman diagrams for ${{\mathrm {W}} {\mathrm {Z}}\mathrm {jj}}$ production in the SM and beyond the SM. The EW-induced component of WZ production includes quartic interactions (left) of the vector bosons. This is distinguishable from QCD-induced production (second from left) through kinematic variables. New physics in the EW sector modifying the quartic coupling can be parameterized in terms of dimension-eight effective field theory operators (third from left). Specific models modifying this interaction include those predicting charged Higgs bosons (right). |
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Figure 1-a:
Representative Feynman diagram for ${{\mathrm {W}} {\mathrm {Z}}\mathrm {jj}}$ production in the SM. The EW-induced component of WZ production includes quartic interactions of the vector bosons. |
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Figure 1-b:
Representative Feynman diagram for ${{\mathrm {W}} {\mathrm {Z}}\mathrm {jj}}$ production in the SM. Here, the QCD-induced production through kinematic variables. |
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Figure 1-c:
Representative Feynman diagram for ${{\mathrm {W}} {\mathrm {Z}}\mathrm {jj}}$ production beyond the SM. New physics in the EW sector modifying the quartic coupling can be parameterized in terms of dimension-eight effective field theory operators. |
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Figure 1-d:
Representative Feynman diagram for ${{\mathrm {W}} {\mathrm {Z}}\mathrm {jj}}$ production beyond the SM. Here, a model with charged Higgs boson exchange. |
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Figure 2:
The $ {m_{\mathrm {jj}}}$ (left) and $ {| {\Delta \eta _{\mathrm {jj}}} |}$ (right) of the two leading jets for events satisfying the EW signal selection. The last bin contains all events with $ {m_{\mathrm {jj}}} > $ 2500 GeV (left) and $ {| {\Delta \eta _{\mathrm {jj}}} |} > $ 7.5 (right). The dashed line shows the expected EW WZ contribution stacked on top of the backgrounds that are shown as filled histograms. The hatched bands represent the total and relative statistical uncertainties on the predicted yields. The bottom panel shows the ratio of the number of events measured in data to the total number of expected events. The predicted yields are shown with their pre-fit normalizations. |
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Figure 2-a:
The $ {m_{\mathrm {jj}}}$ of the two leading jets for events satisfying the EW signal selection. The last bin contains all events with $ {m_{\mathrm {jj}}} > $ 2500 GeV. The dashed line shows the expected EW WZ contribution stacked on top of the backgrounds that are shown as filled histograms. The hatched band represents the total and relative statistical uncertainties on the predicted yields. The bottom panel shows the ratio of the number of events measured in data to the total number of expected events. The predicted yields are shown with their pre-fit normalizations. |
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Figure 2-b:
The $ {| {\Delta \eta _{\mathrm {jj}}} |}$ of the two leading jets for events satisfying the EW signal selection. The last bin contains all events with $ {| {\Delta \eta _{\mathrm {jj}}} |} > $ 7.5. The dashed line shows the expected EW WZ contribution stacked on top of the backgrounds that are shown as filled histograms. The hatched band represents the total and relative statistical uncertainties on the predicted yields. The bottom panel shows the ratio of the number of events measured in data to the total number of expected events. The predicted yields are shown with their pre-fit normalizations. |
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Figure 3:
The one-dimensional representation of the 2D distribution of $ {m_{\mathrm {jj}}}$ and $ {| {\Delta \eta _{\mathrm {jj}}} |}$, used for the EW signal extraction. The x axis shows the ${{m_{\mathrm {jj}}}}$ distribution in the indicated bins, split into three bins of ${{\Delta \eta _{\mathrm {jj}}}}$: ${{\Delta \eta _{\mathrm {jj}}}} \in$ [2.5, 4], [4, 5], $\ge$5. The dashed line represents the EW WZ contribution stacked on top of the backgrounds that are shown as filled histograms. The hatched bands represent the total and relative systematic uncertainties on the predicted yields. The bottom panel shows the ratio of the number of events measured in data to the total number of expected events. The predicted yields are shown with their best-fit normalizations. |
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Figure 4:
$ {m_{\mathrm {T}}({\mathrm {W}} {\mathrm {Z}})}$ for events satisfying the EW signal selection, used to place constraints on the anomalous coupling parameters. The dashed lines show predictions for several aQGC parameters values that modify the EW WZ process. The last bin contains all events with $ {m_{\mathrm {T}}({\mathrm {W}} {\mathrm {Z}})} > $ 2000 GeV. The hatched bands represent the total and relative systematic uncertainties on the predicted yields. The bottom panel shows the ratio of the number of events measured in data to the total number of expected events. The predicted yields are shown with their best-fit normalizations from the background-only fit. |
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Figure 5:
Two-dimensional observed 95% CL intervals (solid contour) and expected 68, 95, and 99% CL intervals (dashed contour) on the selected aQGC parameters. The values of coefficients outside of contours are excluded at the corresponding CL. |
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Figure 5-a:
Two-dimensional observed 95% CL intervals (solid contour) and expected 68, 95, and 99% CL intervals (dashed contour) on selected aQGC parameters. The values of coefficients outside of contours are excluded at the corresponding CL. |
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Figure 5-b:
Two-dimensional observed 95% CL intervals (solid contour) and expected 68, 95, and 99% CL intervals (dashed contour) on selected aQGC parameters. The values of coefficients outside of contours are excluded at the corresponding CL. |
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Figure 6:
$ {m_{\mathrm {T}}({\mathrm {W}} {\mathrm {Z}})}$ for events satisfying the Higgs boson selection, used to place constraints on the production of charged Higgs bosons. The last bin contains all events with $ {m_{\mathrm {T}}({\mathrm {W}} {\mathrm {Z}})} > $ 2000 GeV. The dashed lines show predictions from the GM model with $m({\mathrm {H^{\pm}}}) = $ 400 (900) GeV and $s_{{\mathrm {H}}} = $ 0.3 (0.5). The bottom panel shows the ratio of the number of events measured in data to the total number of expected events. The hatched bands represent the total and relative systematic uncertainties on the predicted background yields. The predicted yields are shown with their best-fit normalizations from the background-only fit. |
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Figure 7:
Expected (dashed lines) and observed (solid lines) upper limits at 95% CL for the model independent $\sigma ({\mathrm {H}} ^{\pm}) \mathcal {B}(H^+\to {\mathrm {W}} {\mathrm {Z}})$ as a function of $m({\mathrm {H}} ^\pm)$ (left) and for $s_{{\mathrm {H}}}$ as a function of $m_{{\mathrm {H}}}$ in the GM model (right). The blue shaded area covers the theoretically not allowed parameter space [69]. |
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Figure 7-a:
Expected (dashed lines) and observed (solid lines) upper limits at 95% CL for the model independent $\sigma ({\mathrm {H}} ^{\pm}) \mathcal {B}(H^+\to {\mathrm {W}} {\mathrm {Z}})$ as a function of $m({\mathrm {H}} ^\pm)$. |
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Figure 7-b:
Expected (dashed lines) and observed (solid lines) upper limits at 95% CL for $s_{{\mathrm {H}}}$ as a function of $m_{{\mathrm {H}}}$ in the GM mode. The blue shaded area covers the theoretically not allowed parameter space [69]. |
| Tables | |
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Table 1:
Summary of event selections and fiducial region definitions for the analysis. The selections labeled "EW signal'' and "Higgs boson'' are applied to data and reconstructed simulated events. The EW signal selection is used for all measurements except for the charged Higgs boson search that uses the selection indicated in the column labeled "Higgs boson.'' The ${{\mathrm {W}} {\mathrm {Z}}\mathrm {jj}}$ cross section is reported in the fiducial regions defined by the selections specified in the last two columns applied to particle-level simulated events. The variables $n_{{\mathrm {j}}}$ and $n_{{\mathrm {b}}}$ refer to the number of anti-$ {k_{\mathrm {T}}}$ jets and the number of anti-$ {k_{\mathrm {T}}}$ b-tagged jets, respectively. Other variables are defined in the text. |
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Table 2:
The dominant systematic uncertainty contributions in the fiducial ${{\mathrm {W}} {\mathrm {Z}}\mathrm {jj}}$ cross section measurement and their expected contributions to the significance of the EW WZ measurement. |
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Table 3:
Post-fit event yields after the signal extraction fit to events satisfying the EW signal selection. The EW WZ process is corrected for the observed value of $\mu _{{\text {EW}}}$. |
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Table 4:
Observed and expected 95% CL limits for each operator coefficient (in TeV$^{-4}$) while all other parameters are set to zero. |
| Summary |
|
A measurement of the production of a W and a Z boson in association with two jets has been presented, using events where both bosons decay leptonically. Results are based on data corresponding to an integrated luminosity of 35.9 fb$^{-1}$ recorded in proton-proton collisions at $\sqrt{s} = $ 13 TeV with the CMS detector at the LHC in 2016. The cross section in a tight fiducial region with enhanced contributions from electroweak (EW) WZ production is $\sigma^{\mathrm{fid}}_{{\mathrm{W}\mathrm{Z}\mathrm{jj}} } = $ 3.18$^{+0.71}_{-0.63}$ fb, consistent with the standard model (SM) prediction. The dijet mass and dijet rapidity separation are used to measure the signal strength of EW WZ production with respect to the SM expectation, resulting in $\mu_{{\text{EW}} } = $ 0.82$^{+0.51}_{-0.43}$. The significance of this result is 2.2 standard deviations with 2.5 standard deviations expected. These are the first results for EW WZ production at 13 TeV. Constraints are placed on anomalous quartic gauge couplings in terms of dimension-eight effective field theory operators, and upper limits are given on the production cross section times branching fraction of charged Higgs bosons. The upper limits on charged Higgs boson production via vector boson fusion with decay to a W and a Z boson extend the results previously published by the CMS Collaboration [59] and are comparable to those of the ATLAS Collaboration [70]. These are the first limits for dimension-eight effective field theory operators in the WZ channel at 13 TeV. |
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