CMS-PAS-FTR-18-036 | ||
Anomalous couplings in the ttZ final state at the HL-LHC | ||
CMS Collaboration | ||
December 2018 | ||
Abstract: The electroweak couplings of the top quark provide a crucial window to physics beyond the standard model and can be put to stringent tests with the CERN High-Luminosity LHC (HL-LHC). The expected sensitivity of the CMS detector for anomalous electroweak top quark interactions based on differential cross section measurements of the ttZ process in the three lepton final state is provided for a HL-LHC scenario with 3000 fb−1 of proton-proton collision data at a centre-of-mass energy of 14 TeV. | ||
Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ; |
Figures & Tables | Summary | Additional Figures & Tables | References | CMS Publications |
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Figures | |
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Figure 1:
Representative Feynman diagram for the ttZ process. |
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Figure 2:
Differential cross sections with respect to pT(Z) (left) and cosθ∗Z (right) in the ttZ (Nlep= 3) channel as specified in Table 2 and for the Phase-2 scenario. For cosθ∗Z, an additional requirement of pT(Z)> 200 GeV is applied. The SM distributions are shown in black with systematic uncertainties, while colored lines show hypotheses for CtZ=2 (Λ/TeV)2 and C[Im]tZ= 2 (Λ/TeV)2, with yields that are area-normalized to the SM distribution. The non-informative contribution to ttZ is described in Sec. 4 and shown hatched. Backgrounds are shown in solid colors. |
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Figure 2-a:
Differential cross sections with respect to pT(Z) in the ttZ (Nlep= 3) channel as specified in Table 2 and for the Phase-2 scenario. For cosθ∗Z, an additional requirement of pT(Z)> 200 GeV is applied. The SM distributions are shown in black with systematic uncertainties, while colored lines show hypotheses for CtZ=2 (Λ/TeV)2 and C[Im]tZ= 2 (Λ/TeV)2, with yields that are area-normalized to the SM distribution. The non-informative contribution to ttZ is described in Sec. 4 and shown hatched. Backgrounds are shown in solid colors. |
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Figure 2-b:
Differential cross sections with respect to cosθ∗Z in the ttZ (Nlep= 3) channel as specified in Table 2 and for the Phase-2 scenario. For cosθ∗Z, an additional requirement of pT(Z)> 200 GeV is applied. The SM distributions are shown in black with systematic uncertainties, while colored lines show hypotheses for CtZ=2 (Λ/TeV)2 and C[Im]tZ= 2 (Λ/TeV)2, with yields that are area-normalized to the SM distribution. The non-informative contribution to ttZ is described in Sec. 4 and shown hatched. Backgrounds are shown in solid colors. |
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Figure 3:
Signal region yields from simulation for SM processes (colored histograms). The yields are estimated for an integrated luminosity of 3/ab, the cross section is scaled to 14 TeV. The total SM yield is shown with the black line, the dashed red line reflects the total expected yield assuming modified couplings, with the chosen value CtZ= 2 (Λ/TeV)2. The hatched area represents the non-informative contribution to ttZ as described in Sec. 4. |
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Figure 4:
Individual likelihood ratio for the Wilson coefficients Cϕt and C−ϕQ (top) and CtZ and C[Im]tZ (bottom) for the ttZ process. Here, only one Wilson coefficient at a time is considered non-zero. The 68% (95%) CL intervals are given in green (red). |
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Figure 4-a:
Individual likelihood ratio for the Wilson coefficients Cϕt for the ttZ process. Other Wilson coefficients are set to zero. The 68% (95%) CL interval is given in green (red). |
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Figure 4-b:
Individual likelihood ratio for the Wilson coefficients C−ϕQ for the ttZ process. Other Wilson coefficients are set to zero. The 68% (95%) CL interval is given in green (red). |
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Figure 4-c:
Individual likelihood ratio for the Wilson coefficients CtZ for the ttZ process. Other Wilson coefficients are set to zero. The 68% (95%) CL interval is given in green (red). |
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Figure 4-d:
Individual likelihood ratio for the Wilson coefficients C[Im]tZ for the ttZ process. Other Wilson coefficients are set to zero. The 68% (95%) CL interval is given in green (red). |
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Figure 5:
Individual profiled likelihood ratio for the Wilson coefficients Cϕt and C−ϕQ (top) and CtZ and C[Im]tZ (bottom) for the ttZ process under the SM hypothesis. The 68% (95%) CL intervals are given in green (red). |
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Figure 5-a:
Individual profiled likelihood ratio for the Wilson coefficients Cϕt for the ttZ process under the SM hypothesis. The 68% (95%) CL intervals are given in green (red). |
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Figure 5-b:
Individual profiled likelihood ratio for the Wilson coefficients C−ϕQ for the ttZ process under the SM hypothesis. The 68% (95%) CL intervals are given in green (red). |
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Figure 5-c:
Individual profiled likelihood ratio for the Wilson coefficients CtZ for the ttZ process under the SM hypothesis. The 68% (95%) CL intervals are given in green (red). |
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Figure 5-d:
Individual profiled likelihood ratio for the Wilson coefficients C[Im]tZ for the ttZ process under the SM hypothesis. The 68% (95%) CL intervals are given in green (red). |
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Figure 6:
Scan of the negative likelihood in the C−ϕQ/Cϕt (left) and CtZ/C[Im]tZ parameter planes (right) for the ttZ process under the SM hypothesis. The 68% (95%) CL contour lines are given in green (red). |
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Figure 6-a:
Scan of the negative likelihood in the C−ϕQ/Cϕt parameter plane for the ttZ process under the SM hypothesis. The 68% (95%) CL contour lines are given in green (red). |
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Figure 6-b:
Scan of the negative likelihood in the CtZ/C[Im]tZ parameter plane for the ttZ process under the SM hypothesis. The 68% (95%) CL contour lines are given in green (red). |
Tables | |
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Table 1:
Simulated processes with a Monte-Carlo sample size of one million events, the cross section for √s=13TeV and the scale factor for √s= 14 TeV . Here, ℓ= e, μ, τ and νℓ=νe, νμ, ντ. |
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Table 2:
Event selection and object level thresholds for the ttZ selection. |
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Table 3:
Definition of the ttZ signal regions. |
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Table 4:
The sources of systematic uncertainty grouped in experimental systematic uncertainties (exp.) and theoretical uncertainties (theo.) as well as their impacts on reconstructed objects and event yields. |
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Table 5:
Expected 68% and 95% CL intervals, where one Wilson coefficient at a time is considered non-zero. |
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Table 6:
Expected 68% and 95% CL intervals for the selected Wilson coefficients in a profiled scan over the 2D parameter planes C−ϕQ/Cϕt and CtZ/C[Im]tZ. The respective second parameter of the scan is left free. |
Summary |
The CMS sensitivity to anomalous interactions using ttZ measurements in the HL-LHC era corresponding to a simulated data set of 3 ab−1 of integrated luminosity has been been estimated in the context of SM-EFT. The considered scenario assumed advances in both experimental methods and theoretical descriptions of the relevant physics effects. With the reduced theoretical and experimental uncertainties, tight constraints are expected in two planes spanned by a total of four Wilson coefficients and in one dimensional log-likelihood scans. |
Additional Figures | |
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Additional Figure 1:
Scan of the negative likelihood in the C1V/C1A parameter plane for the ttZ process under the SM hypothesis. The 68% (95%) CL contour lines are given in green (red). Parameter definition according to [41,45]. The Standard Model values for C1V and C1A correspond to 0.244 and -0.601 respectively. |
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Additional Figure 2:
Scan of the negative likelihood in the C2V/C2A parameter plane for the ttZ process under the SM hypothesis. The 68% (95%) CL contour lines are given in green (red). Parameter definition according to [41,45]. |
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Additional Figure 3:
Profiled likelihood ratio for the Wilson coefficient C1V for the ttZ process under the SM hypothesis. The 68% (95%) CL intervals are given in green (red). Parameter definition according to [41,45]. The Standard Model value for C1V corresponds to 0.244. |
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Additional Figure 4:
Profiled likelihood ratio for the Wilson coefficient C1A for the ttZ process under the SM hypothesis. The 68% (95%) CL intervals are given in green (red). Parameter definition according to [41,45]. The Standard Model value for C1A corresponds to -0.601. |
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Additional Figure 5:
Profiled likelihood ratio for the Wilson coefficient C2V for the ttZ process under the SM hypothesis. The 68% (95%) CL intervals are given in green (red). Parameter definition according to [41,45]. |
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Additional Figure 6:
Profiled likelihood ratio for the Wilson coefficient C2A for the ttZ process under the SM hypothesis. The 68% (95%) CL intervals are given in green (red). Parameter definition according to [41,45]. |
Additional Tables | |
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Additional Table 1:
Expected 68 % and 95 % CL intervals for the selected anomalous coupling parameters in a profiled scan over the 2D parameter planes C1V/C1A and C2V/C2A. The respective second parameter of the scan is left free. Parameter definition according to [41,45]. The Standard Model values for C1V and C1A correspond to 0.244 and -0.601 respectively. |
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Additional Table 2:
Expected 68 % and 95 % CL intervals for the selected anomalous coupling parameters in a profiled scan over the 2D parameter planes δXLtt/δXRtt and δdZV/δdZA. The respective second parameter of the scan is left free. Parameter definition according to [45]. |
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Additional Table 3:
Expected 68 % and 95 % CL intervals, where one anomalous coupling parameter at a time is considered non-zero. Parameter definition according to [45]. |
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Compact Muon Solenoid LHC, CERN |
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