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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
png pdf	Figure 1: Representative Feynman diagram for the ttZ process.
png pdf	Figure 2: Differential cross sections with respect to $ { {p_\textrm {T}} ({\mathrm {Z}})} $ (left) and $\cos\theta ^\ast _{{\mathrm {Z}}}$ (right) in the ttZ (${N_{\textrm {lep}}}= $ 3) channel as specified in Table 2 and for the Phase-2 scenario. For $\cos\theta ^\ast _{{\mathrm {Z}}}$, an additional requirement of $ { {p_\textrm {T}} ({\mathrm {Z}})} > $ 200 GeV is applied. The SM distributions are shown in black with systematic uncertainties, while colored lines show hypotheses for ${C_\text {tZ}} $=2 ($\Lambda $/TeV)$^2$ and ${C_\text {tZ}^\text {[Im]}} = $ 2 ($\Lambda $/TeV)$^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.
png pdf	Figure 2-a: Differential cross sections with respect to $ { {p_\textrm {T}} ({\mathrm {Z}})} $ in the ttZ (${N_{\textrm {lep}}}= $ 3) channel as specified in Table 2 and for the Phase-2 scenario. For $\cos\theta ^\ast _{{\mathrm {Z}}}$, an additional requirement of $ { {p_\textrm {T}} ({\mathrm {Z}})} > $ 200 GeV is applied. The SM distributions are shown in black with systematic uncertainties, while colored lines show hypotheses for ${C_\text {tZ}} $=2 ($\Lambda $/TeV)$^2$ and ${C_\text {tZ}^\text {[Im]}} = $ 2 ($\Lambda $/TeV)$^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.
png pdf	Figure 2-b: Differential cross sections with respect to $\cos\theta ^\ast _{{\mathrm {Z}}}$ in the ttZ (${N_{\textrm {lep}}}= $ 3) channel as specified in Table 2 and for the Phase-2 scenario. For $\cos\theta ^\ast _{{\mathrm {Z}}}$, an additional requirement of $ { {p_\textrm {T}} ({\mathrm {Z}})} > $ 200 GeV is applied. The SM distributions are shown in black with systematic uncertainties, while colored lines show hypotheses for ${C_\text {tZ}} $=2 ($\Lambda $/TeV)$^2$ and ${C_\text {tZ}^\text {[Im]}} = $ 2 ($\Lambda $/TeV)$^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.
png pdf	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 ${C_\text {tZ}} = $ 2 ($\Lambda $/TeV)$^2$. The hatched area represents the non-informative contribution to ttZ as described in Sec. 4.
png pdf	Figure 4: Individual likelihood ratio for the Wilson coefficients $ {C_{\phi t}} $ and ${C_{\phi Q}^{-}}$ (top) and ${C_\text {tZ}}$ and ${C_\text {tZ}^\text {[Im]}}$ (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).
png pdf	Figure 4-a: Individual likelihood ratio for the Wilson coefficients $ {C_{\phi t}} $ for the ttZ process. Other Wilson coefficients are set to zero. The 68% (95%) CL interval is given in green (red).
png pdf	Figure 4-b: Individual likelihood ratio for the Wilson coefficients ${C_{\phi Q}^{-}}$ for the ttZ process. Other Wilson coefficients are set to zero. The 68% (95%) CL interval is given in green (red).
png pdf	Figure 4-c: Individual likelihood ratio for the Wilson coefficients ${C_\text {tZ}}$ for the ttZ process. Other Wilson coefficients are set to zero. The 68% (95%) CL interval is given in green (red).
png pdf	Figure 4-d: Individual likelihood ratio for the Wilson coefficients ${C_\text {tZ}^\text {[Im]}}$ for the ttZ process. Other Wilson coefficients are set to zero. The 68% (95%) CL interval is given in green (red).
png pdf	Figure 5: Individual profiled likelihood ratio for the Wilson coefficients $ {C_{\phi t}} $ and ${C_{\phi Q}^{-}}$ (top) and ${C_\text {tZ}}$ and ${C_\text {tZ}^\text {[Im]}}$ (bottom) for the ttZ process under the SM hypothesis. The 68% (95%) CL intervals are given in green (red).
png pdf	Figure 5-a: Individual profiled likelihood ratio for the Wilson coefficients $ {C_{\phi t}} $ for the ttZ process under the SM hypothesis. The 68% (95%) CL intervals are given in green (red).
png pdf	Figure 5-b: Individual profiled likelihood ratio for the Wilson coefficients ${C_{\phi Q}^{-}}$ for the ttZ process under the SM hypothesis. The 68% (95%) CL intervals are given in green (red).
png pdf	Figure 5-c: Individual profiled likelihood ratio for the Wilson coefficients ${C_\text {tZ}}$ for the ttZ process under the SM hypothesis. The 68% (95%) CL intervals are given in green (red).
png pdf	Figure 5-d: Individual profiled likelihood ratio for the Wilson coefficients ${C_\text {tZ}^\text {[Im]}}$ for the ttZ process under the SM hypothesis. The 68% (95%) CL intervals are given in green (red).
png pdf	Figure 6: Scan of the negative likelihood in the ${C_{\phi Q}^{-}} / {C_{\phi t}}$ (left) and ${C_\text {tZ}} / {C_\text {tZ}^\text {[Im]}}$ parameter planes (right) for the ttZ process under the SM hypothesis. The 68% (95%) CL contour lines are given in green (red).
png pdf	Figure 6-a: Scan of the negative likelihood in the ${C_{\phi Q}^{-}} / {C_{\phi t}}$ parameter plane for the ttZ process under the SM hypothesis. The 68% (95%) CL contour lines are given in green (red).
png pdf	Figure 6-b: Scan of the negative likelihood in the ${C_\text {tZ}} / {C_\text {tZ}^\text {[Im]}}$ parameter plane for the ttZ process under the SM hypothesis. The 68% (95%) CL contour lines are given in green (red).

Tables
png pdf	Table 1: Simulated processes with a Monte-Carlo sample size of one million events, the cross section for $\sqrt {s}=13 TeV $ and the scale factor for $\sqrt {s}=$ 14 TeV . Here, $\ell =$ e, $\mu$, $\tau $ and $\nu _\ell =\nu _e$, $\nu _\mu$, $\nu _\tau $.
png pdf	Table 2: Event selection and object level thresholds for the ttZ selection.
png pdf	Table 3: Definition of the ttZ signal regions.
png pdf	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.
png pdf	Table 5: Expected 68% and 95% CL intervals, where one Wilson coefficient at a time is considered non-zero.
png pdf	Table 6: Expected 68% and 95% CL intervals for the selected Wilson coefficients in a profiled scan over the 2D parameter planes ${C_{\phi Q}^{-}} / {C_{\phi t}}$ and ${C_\text {tZ}} / {C_\text {tZ}^\text {[Im]}}$. 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
png pdf	Additional Figure 1: Scan of the negative likelihood in the $C_\text {1V}$/$C_\text {1A}$ 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 $C_\text {1V}$ and $C_\text {1A}$ correspond to 0.244 and -0.601 respectively.
png pdf	Additional Figure 2: Scan of the negative likelihood in the $C_\text {2V}$/$C_\text {2A}$ 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].
png pdf	Additional Figure 3: Profiled likelihood ratio for the Wilson coefficient $C_\text {1V}$ 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 $C_\text {1V}$ corresponds to 0.244.
png pdf	Additional Figure 4: Profiled likelihood ratio for the Wilson coefficient $C_\text {1A}$ 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 $C_\text {1A}$ corresponds to -0.601.
png pdf	Additional Figure 5: Profiled likelihood ratio for the Wilson coefficient $C_\text {2V}$ for the ttZ process under the SM hypothesis. The 68% (95%) CL intervals are given in green (red). Parameter definition according to [41,45].
png pdf	Additional Figure 6: Profiled likelihood ratio for the Wilson coefficient $C_\text {2A}$ 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
png pdf	Additional Table 1: Expected 68 % and 95 % CL intervals for the selected anomalous coupling parameters in a profiled scan over the 2D parameter planes $C_\text {1V}$/$C_\text {1A}$ and $C_\text {2V}$/$C_\text {2A}$. The respective second parameter of the scan is left free. Parameter definition according to [41,45]. The Standard Model values for $C_\text {1V}$ and $C_\text {1A}$ correspond to 0.244 and -0.601 respectively.
png pdf	Additional Table 2: Expected 68 % and 95 % CL intervals for the selected anomalous coupling parameters in a profiled scan over the 2D parameter planes $\delta X_{t t}^{L}$/$\delta X_{t t}^{R}$ and $\delta d_{V}^{Z}$/$\delta d_{A}^{Z}$. The respective second parameter of the scan is left free. Parameter definition according to [45].
png pdf	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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