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| CMS-PAS-TOP-19-001 | ||
| Using associated top quark production to probe for new physics within the framework of effective field theory | ||
| CMS Collaboration | ||
| July 2020 | ||
| Abstract: A data sample consisting of one or more top quarks produced in association with additional leptons is used to search for signs of new physics within the framework of effective field theory (EFT). This data sample corresponds to an integrated luminosity of 41.5 fb$^{-1}$ of proton-proton collisions produced in 2017 at a center-of-mass energy of 13 TeV at the LHC and collected by the CMS experiment. The sample is selected by requiring events with multiple leptons and jets, including identified bottom quark jets; the events are then divided into categories based on the multiplicities of these objects. Sixteen dimension-six operators that can affect associated top quark production processes are considered in this analysis. Constructed to target EFT effects directly, the analysis applies a novel approach in which the observed yields are parameterized in terms of the Wilson coefficients (WCs) of the EFT operators. A fit is performed simultaneously of the 16 WCs to the data and limits on the values of the WCs are presented. The observed data are statistically consistent with standard model expectations, so the possibility of new physics is characterized in terms of 2 standard deviation confidence intervals for the WCs. | ||
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CDS record (PDF) ;
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These preliminary results are superseded in this paper, JHEP 03 (2021) 095. The superseded preliminary plots can be found here. |
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| Figures & Tables | Summary | Additional Figures | References | CMS Publications |
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| Figures | |
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Figure 1:
Example Feynman diagrams for the five signal processes considered in this analysis: ${\rm {\mathrm{t}} {\mathrm{\bar{t}}} {\mathrm {H}}}$, ${\rm {\mathrm{t}} {\mathrm{\bar{t}}}\ell \bar{\ell}}$, ${{\mathrm{t}} {\mathrm{\bar{t}}}\ell {\nu}}$, ${\rm {\mathrm{t}}\ell \bar{\ell} {\mathrm{q}}}$, and ${\rm {\mathrm{t}} {\mathrm {H}} {\mathrm{q}}}$. |
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Figure 1-a:
Example Feynman diagram for the ${\rm {\mathrm{t}} {\mathrm{\bar{t}}} {\mathrm {H}}}$ signal process. |
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Figure 1-b:
Example Feynman diagram for the ${\rm {\mathrm{t}} {\mathrm{\bar{t}}}\ell \bar{\ell}}$ signal process. |
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Figure 1-c:
Example Feynman diagram for the ${{\mathrm{t}} {\mathrm{\bar{t}}}\ell {\nu}}$ signal process. |
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Figure 1-d:
Example Feynman diagram for the ${\rm {\mathrm{t}}\ell \bar{\ell} {\mathrm{q}}}$ signal process. |
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Figure 1-e:
Example Feynman diagram for the ${\rm {\mathrm{t}} {\mathrm {H}} {\mathrm{q}}}$ signal process. |
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Figure 2:
Example Feynman diagrams showing two of the vertices associated with the $O_{\mathrm{u} G}$ operator. This operator, whose definition can be found in Table 1, gives rise to vertices involving top quarks, gluons, and the Higgs boson; as illustrated here, these interactions can contribute to the ${\rm {\mathrm{t}} {\mathrm{\bar{t}}} {\mathrm {H}}}$ process. |
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Figure 3:
Expected yields prefit (left) and postfit (right). The postfit values of the WCs are obtained from performing the fit over all WCs simultaneously. "Convs" refers to the photon conversion background, "ChargeFlips" is the lepton charge mismeasurement background, and "Fakes" is the background from misidentified leptons. |
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Figure 3-a:
Legend of the following plots. "Convs" refers to the photon conversion background, "ChargeFlips" is the lepton charge mismeasurement background, and "Fakes" is the background from misidentified leptons. |
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Figure 3-b:
Expected yields prefit. |
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Figure 3-c:
Expected yields postfit. The postfit values of the WCs are obtained from performing the fit over all WCs simultaneously. |
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Figure 4:
Observed WC 1$\sigma $ (thick line) and 2$\sigma $ (thin line) confidence intervals. Solid lines correspond to the other WCs profiled, while dashed lines correspond to the other WCs fixed to the SM value of zero. |
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Figure 5:
The observed 1$\sigma $, 2$\sigma $, and 3$\sigma $ confidence contours of a 2D scan for ${{c^{-({\ell})}_{Q {\ell}}}}$ and ${{c^{({\ell})}_{Q\mathrm{e}}}}$ with the other WCs profiled (left), and fixed to their SM values (right). Diamond markers are shown for the SM prediction. |
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Figure 5-a:
The observed 1$\sigma $, 2$\sigma $, and 3$\sigma $ confidence contours of a 2D scan for ${{c^{-({\ell})}_{Q {\ell}}}}$ and ${{c^{({\ell})}_{Q\mathrm{e}}}}$ with the other WCs profiled. Diamond markers are shown for the SM prediction. |
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Figure 5-b:
The observed 1$\sigma $, 2$\sigma $, and 3$\sigma $ confidence contours of a 2D scan for ${{c^{-({\ell})}_{Q {\ell}}}}$ and ${{c^{({\ell})}_{Q\mathrm{e}}}}$ with the other WCs fixed to their SM values. Diamond markers are shown for the SM prediction. |
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Figure 6:
The observed 1$\sigma $, 2$\sigma $, and 3$\sigma $ confidence contours of a 2D scan for ${{c_{\varphi \mathrm{t} \mathrm{b}}}}$ and ${{c^{3({\ell})}_{Q {\ell}}}}$ with the other WCs profiled (left), and fixed to their SM values (right). Diamond markers are shown for the SM prediction. |
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Figure 6-a:
The observed 1$\sigma $, 2$\sigma $, and 3$\sigma $ confidence contours of a 2D scan for ${{c_{\varphi \mathrm{t} \mathrm{b}}}}$ and ${{c^{3({\ell})}_{Q {\ell}}}}$ with the other WCs profiled. Diamond markers are shown for the SM prediction. |
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Figure 6-b:
The observed 1$\sigma $, 2$\sigma $, and 3$\sigma $ confidence contours of a 2D scan for ${{c_{\varphi \mathrm{t} \mathrm{b}}}}$ and ${{c^{3({\ell})}_{Q {\ell}}}}$ with the other WCs fixed to their SM values. Diamond markers are shown for the SM prediction. |
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Figure 7:
The observed 1$\sigma $, 2$\sigma $, and 3$\sigma $ confidence contours of a 2D scan for ${{c^{3}_{\varphi Q}}}$ and ${{c_{\mathrm{b} \mathrm{W}}}}$ with the other WCs profiled (left), and fixed to their SM values (right). Diamond markers are shown for the SM prediction. |
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Figure 7-a:
The observed 1$\sigma $, 2$\sigma $, and 3$\sigma $ confidence contours of a 2D scan for ${{c^{3}_{\varphi Q}}}$ and ${{c_{\mathrm{b} \mathrm{W}}}}$ with the other WCs profiled. Diamond markers are shown for the SM prediction. |
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Figure 7-b:
The observed 1$\sigma $, 2$\sigma $, and 3$\sigma $ confidence contours of a 2D scan for ${{c^{3}_{\varphi Q}}}$ and ${{c_{\mathrm{b} \mathrm{W}}}}$ with the other WCs fixed to their SM values. Diamond markers are shown for the SM prediction. |
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Figure 8:
The observed 1$\sigma $, 2$\sigma $, and 3$\sigma $ confidence contours of a 2D scan for ${{c_{\mathrm{t} G}}}$ and ${{c^{-}_{\varphi Q}}}$ with the other WCs profiled (left), and fixed to their SM values (right). Diamond markers are shown for the SM prediction. |
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Figure 8-a:
The observed 1$\sigma $, 2$\sigma $, and 3$\sigma $ confidence contours of a 2D scan for ${{c_{\mathrm{t} G}}}$ and ${{c^{-}_{\varphi Q}}}$ with the other WCs profiled. Diamond markers are shown for the SM prediction. |
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Figure 8-b:
The observed 1$\sigma $, 2$\sigma $, and 3$\sigma $ confidence contours of a 2D scan for ${{c_{\mathrm{t} G}}}$ and ${{c^{-}_{\varphi Q}}}$ with the other WCs fixed to their SM values. Diamond markers are shown for the SM prediction. |
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Figure 9:
The observed 1$\sigma $, 2$\sigma $, and 3$\sigma $ confidence contours of a 2D scan for ${{c_{\mathrm{t} \varphi}}}$ and ${{c_{\varphi \mathrm{t}}}}$ with the other WCs profiled (left), and fixed to their SM values (right). Diamond markers are shown for the SM prediction. |
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Figure 9-a:
The observed 1$\sigma $, 2$\sigma $, and 3$\sigma $ confidence contours of a 2D scan for ${{c_{\mathrm{t} \varphi}}}$ and ${{c_{\varphi \mathrm{t}}}}$ with the other WCs profiled. Diamond markers are shown for the SM prediction. |
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Figure 9-b:
The observed 1$\sigma $, 2$\sigma $, and 3$\sigma $ confidence contours of a 2D scan for ${{c_{\mathrm{t} \varphi}}}$ and ${{c_{\varphi \mathrm{t}}}}$ with the other WCs fixed to their SM values. Diamond markers are shown for the SM prediction. |
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Figure 10:
The observed 1$\sigma $, 2$\sigma $, and 3$\sigma $ confidence contours of a 2D scan for ${{c_{\mathrm{t} \mathrm{Z}}}}$ and ${{c_{\mathrm{t} \mathrm{W}}}}$ with the other WCs profiled (left), and fixed to their SM values (right). Diamond markers are shown for the SM prediction. |
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Figure 10-a:
The observed 1$\sigma $, 2$\sigma $, and 3$\sigma $ confidence contours of a 2D scan for ${{c_{\mathrm{t} \mathrm{Z}}}}$ and ${{c_{\mathrm{t} \mathrm{W}}}}$ with the other WCs profiled. Diamond markers are shown for the SM prediction. |
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Figure 10-b:
The observed 1$\sigma $, 2$\sigma $, and 3$\sigma $ confidence contours of a 2D scan for ${{c_{\mathrm{t} \mathrm{Z}}}}$ and ${{c_{\mathrm{t} \mathrm{W}}}}$ with the other WCs fixed to their SM values. Diamond markers are shown for the SM prediction. |
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Figure 11:
Plots showing the relative change in the expected yield for the signal processes in each event category. $\Delta $Yield refers to the change in expected yield between before fitting (prefit) values and after fitting simultaneously fitting the 16 WCs and nuisance parameters (postfit) values. The error bars represent the maximum variation for a given WC within the corresponding 2$\sigma $ confidence interval. |
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Figure 11-a:
Legend of the following plots. |
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Figure 11-b:
Plots showing the relative change in the expected yield for the signal processes in each event category. $\Delta $Yield refers to the change in expected yield between before fitting (prefit) values and after fitting simultaneously fitting the 16 WCs and nuisance parameters (postfit) values. The error bars represent the maximum variation for a given WC within the corresponding 2$\sigma $ confidence interval. |
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Figure 11-c:
Plots showing the relative change in the expected yield for the signal processes in each event category. $\Delta $Yield refers to the change in expected yield between before fitting (prefit) values and after fitting simultaneously fitting the 16 WCs and nuisance parameters (postfit) values. The error bars represent the maximum variation for a given WC within the corresponding 2$\sigma $ confidence interval. |
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Figure 11-d:
Plots showing the relative change in the expected yield for the signal processes in each event category. $\Delta $Yield refers to the change in expected yield between before fitting (prefit) values and after fitting simultaneously fitting the 16 WCs and nuisance parameters (postfit) values. The error bars represent the maximum variation for a given WC within the corresponding 2$\sigma $ confidence interval. |
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Figure 11-e:
Plots showing the relative change in the expected yield for the signal processes in each event category. $\Delta $Yield refers to the change in expected yield between before fitting (prefit) values and after fitting simultaneously fitting the 16 WCs and nuisance parameters (postfit) values. The error bars represent the maximum variation for a given WC within the corresponding 2$\sigma $ confidence interval. |
| Tables | |
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Table 1:
The list of operators that have effects on ${\rm {\mathrm{t}} {\mathrm{\bar{t}}} {\mathrm {H}}}$, $ {\rm {\mathrm{t}} {\mathrm{\bar{t}}}\ell \bar{\ell}} $, $ {{\mathrm{t}} {\mathrm{\bar{t}}}\ell {\nu}} $, $ {\rm {\mathrm{t}}\ell \bar{\ell} {\mathrm{q}}} $ and $ {\rm {\mathrm{t}} {\mathrm {H}} {\mathrm{q}}} $ processes at order $1/\lambda ^2$ and that are considered in this analysis. The couplings are assumed to involve only third-generation quarks. The field $\varphi $ ($\tilde{\varphi}=\varepsilon \varphi ^*$) is the Higgs boson doublet. The $ {\ell}$ and $\mathrm{q} $ represent the left-handed lepton and quark doublets, respectively, while $\mathrm{e} $ represents the right-handed lepton, and $\mathrm{u} $ and $\mathrm{d} $ represent the right-handed quark singlets. The quantity $T^A= ({1}/{2})\lambda ^A$ denotes the eight Gell-Mann matrices. The covariant derivative is given by $D_\mu =\partial _\mu -ig_s(1/2)\lambda ^AG_\mu ^A-ig(1/2)\tau ^I\mathrm{W} _\mu ^I-ig'Y\mathrm{B} _\mu $. The W boson field strength is $\mathrm{W} _{\mu \nu}^I=\partial _\mu \mathrm{W} _\nu ^I-\partial _\nu \mathrm{W} ^I_\mu +g\varepsilon _{IJK}\mathrm{W} ^J_\mu \mathrm{W} ^K_\nu $, and $G_{\mu \nu}^A=\partial _\mu G_\nu ^A-\partial _\nu G^A_\mu +g_sf^{ABC}G^B_\mu G^C_\nu $ is the gluon field strength. The abbreviations ${s_{\mathrm {W}}}$ and ${c_{\mathrm {W}}}$ denote the sine and cosine of the weak mixing angle (in the unitary gauge). More details about the operators can be found in Ref. [35]. The processes considered to be affected by the operators are also listed (the details of the criteria used for this determination are described in the text). |
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Table 2:
Requirements for the different event categories. Requirements separated by commas indicate a division into subcategories. The $\mathrm{b} $ jet requirement on individual jets varies based on lepton category as described in the text. |
| Summary |
| A search for signal of new physics has been performed in the production of one or more top quarks in association with additional leptons in the context of an effective field theory. The sample of pp collisions corresponding to 41.5 fb$^{-1}$ was selected by requiring events with multiple leptons and jets, including b tagged jets. Selected events were divided into categories depending on the number of leptons, jets, and b jets, and the expected yield in each category was parameterized in terms of 16 Wilson coefficients (WC) associated with effective field theory operators relevant to the dominant processes in the selected data. A fit was performed simultaneously in the 16 WCs to the data. For each WC, an interval over which the model predictions agree with the observed yields at the 2 standard deviation ($\sigma$) level was extracted under two assumptions: either keeping the other WCs fixed to zero or profiling the other WCs. Furthermore, the dependence of these one-dimensional intervals was explored by examining selected two-dimensional contours that illustrate particularly interesting features. The current results from fitting the WCs in the dimension-six model to the data are consistent with the standard model predictions at the 2$\sigma$ level. |
| Additional Figures | |
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Additional Figure 1:
The 1D likelihood scans for the Wilson coefficient (WC) $c_{\mathrm{t}}^{\mathrm{S}(\ell)}$. This fit was made by either profiling the other WCs, or by fixing the other coefficients to their Standard Model value of 0. These two results are overlaid with lines at the 1$\sigma$ and 2$\sigma$ uncertainty value for both. |
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Additional Figure 2:
Legend of the following plots. "Conv." refers to the photon conversion background, "Charge misid." is the lepton charge mismeasurement background, and "Misid. leptons" is the background from misidentified leptons |
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Additional Figure 2-a:
Expected yields when setting the Wilson coefficients (WC) to 1/6 of their final values. The nuisance parameters are all kept at their final post t values. The postfit values of the WCs are obtained from performing the fit over all WCs simultaneously. |
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Additional Figure 2-b:
Expected yields when setting the Wilson coefficients (WC) to 2/6 of their final values. The nuisance parameters are all kept at their final post t values. The postfit values of the WCs are obtained from performing the fit over all WCs simultaneously. |
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Additional Figure 2-c:
Expected yields when setting the Wilson coefficients (WC) to 3/6 of their final values. The nuisance parameters are all kept at their final post t values. The postfit values of the WCs are obtained from performing the fit over all WCs simultaneously. |
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Additional Figure 2-d:
Expected yields when setting the Wilson coefficients (WC) to 4/6 of their final values. The nuisance parameters are all kept at their final post t values. The postfit values of the WCs are obtained from performing the fit over all WCs simultaneously. |
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Additional Figure 2-e:
Expected yields when setting the Wilson coefficients (WC) to 5/6 of their final values. The nuisance parameters are all kept at their final post t values. The postfit values of the WCs are obtained from performing the fit over all WCs simultaneously. |
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