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| CMS-PAS-TOP-15-018 | ||
| Template measurement of the top quark forward-backward asymmetry and anomalous chromoelectric and chromomagnetic moments in the semileptonic channel at $\sqrt{s}=$ 13 TeV | ||
| CMS Collaboration | ||
| September 2019 | ||
| Abstract: The linearized parton-level top quark forward-backward asymmetry $A^{(1)}_{\mathrm{FB}}$ and anomalous chromoelectric ($d$) and chromomagnetic ($\mu$) moments are measured in 35.9 fb$^{-1}$ of LHC proton-proton collision data collected with the CMS detector in 2016 at a center-of-mass energy 13 TeV. Candidate top quark/antiquark pair events decaying to lepton (muon or electron) plus jets final states with "resolved" (low energy) and "boosted" (high energy) topologies are selected and reconstructed using a kinematic fit of the decay products to top quark pair hypotheses. Parameters of interest are measured using binned likelihood fits to observed data of differential models based on extensions to tree-level cross sections for quark-antiquark and gluon-gluon initial states, and are determined to be $A^{(1)}_{\mathrm{FB}}=$ 0.048$^{+0.088}_{-0.084}$(stat) $\pm$ 0.028 (syst), $d=$ 0.002 $\pm$ 0.010 (stat) $^{+0.014}_{-0.019}$ (syst), and $\mu=$ -0.024 $^{+0.013}_{-0.007}$(stat) $^{+0.016}_{-0.006}$ (syst). The forward-backward asymmetry measured using this technique is directly comparable to similar quantities derived from Tevatron measurements. | ||
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Links:
CDS record (PDF) ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, JHEP 06 (2020) 146. The superseded preliminary plots can be found here. |
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| Figures | |
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Figure 1:
(a) Feynman diagrams for the leading order (LO) quark-antiquark (${\mathrm{q} \mathrm{\bar{q}}}$) and gluon-gluon (gg) initiated subprocesses. (b) Example diagrams for the next-to-leading order (NLO) quark-gluon (${\mathrm{q}}{\mathrm{g}}$) initiated subprocess. |
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Figure 2:
The generator-level ${c^{*}}$ (top left), ${x_{F}}$ (top right), and ${m_{{\mathrm{t} {}\mathrm{\bar{t}}}}}$ (bottom left) distributions for the subprocesses $ {\mathrm{q} \mathrm{\bar{q}}} / {\mathrm{q}}{\mathrm{g}}/ {\mathrm{g}}{\mathrm{g}}\to {\mathrm{t} {}\mathrm{\bar{t}}} $. The result of taking the longitudinal direction of the ${\mathrm{t} {}\mathrm{\bar{t}}}$ pair in the lab frame as the quark direction for ${\mathrm{q} \mathrm{\bar{q}}}$ events is shown in the bottom right plot. |
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Figure 2-a:
The generator-level ${c^{*}}$ distribution for the subprocesses $ {\mathrm{q} \mathrm{\bar{q}}} / {\mathrm{q}}{\mathrm{g}}/ {\mathrm{g}}{\mathrm{g}}\to {\mathrm{t} {}\mathrm{\bar{t}}} $. |
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Figure 2-b:
The generator-level ${x_{F}}$ distribution for the subprocesses $ {\mathrm{q} \mathrm{\bar{q}}} / {\mathrm{q}}{\mathrm{g}}/ {\mathrm{g}}{\mathrm{g}}\to {\mathrm{t} {}\mathrm{\bar{t}}} $. |
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Figure 2-c:
The generator-level ${m_{{\mathrm{t} {}\mathrm{\bar{t}}}}}$ distribution for the subprocesses $ {\mathrm{q} \mathrm{\bar{q}}} / {\mathrm{q}}{\mathrm{g}}/ {\mathrm{g}}{\mathrm{g}}\to {\mathrm{t} {}\mathrm{\bar{t}}} $. |
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Figure 2-d:
The result of taking the longitudinal direction of the ${\mathrm{t} {}\mathrm{\bar{t}}}$ pair in the lab frame as the quark direction for ${\mathrm{q} \mathrm{\bar{q}}}$ events is shown. |
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Figure 3:
Data/MC comparison of reconstructed ${c^{*}_{\mathrm {r}}}$ (top), $ {| {x_{\mathrm {r}}} |}$ (middle), and ${m_{\mathrm {r}}}$ (bottom) for events passing full type-1 $\mu$+jets (left column) and e+jets (right column) selection criteria. The MC signal and background show their nominal, pre-fit predictions, and the MC uncertainty pictured in the hatched bands represents statistical errors only. Contribution from QCD multijet background is estimated using the data-driven method described in Section 5. The lower panels of each figure show the ratio of the observed data and total prediction in each bin. |
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Figure 3-a:
Data/MC comparison of reconstructed ${c^{*}_{\mathrm {r}}}$ for events passing full type-1 $\mu$+jets selection criteria. The MC signal and background show their nominal, pre-fit predictions, and the MC uncertainty pictured in the hatched bands represents statistical errors only. Contribution from QCD multijet background is estimated using the data-driven method described in Section 5. The lower panel shows the ratio of the observed data and total prediction in each bin. |
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Figure 3-b:
Data/MC comparison of reconstructed ${c^{*}_{\mathrm {r}}}$ for events passing full type-1 e+jets selection criteria. The MC signal and background show their nominal, pre-fit predictions, and the MC uncertainty pictured in the hatched bands represents statistical errors only. Contribution from QCD multijet background is estimated using the data-driven method described in Section 5. The lower panel shows the ratio of the observed data and total prediction in each bin. |
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Figure 3-c:
Data/MC comparison of reconstructed $ {| {x_{\mathrm {r}}} |}$ for events passing full type-1 $\mu$+jets selection criteria. The MC signal and background show their nominal, pre-fit predictions, and the MC uncertainty pictured in the hatched bands represents statistical errors only. Contribution from QCD multijet background is estimated using the data-driven method described in Section 5. The lower panel shows the ratio of the observed data and total prediction in each bin. |
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Figure 3-d:
Data/MC comparison of reconstructed $ {| {x_{\mathrm {r}}} |}$ for events passing full type-1 e+jets selection criteria. The MC signal and background show their nominal, pre-fit predictions, and the MC uncertainty pictured in the hatched bands represents statistical errors only. Contribution from QCD multijet background is estimated using the data-driven method described in Section 5. The lower panel shows the ratio of the observed data and total prediction in each bin. |
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Figure 3-e:
Data/MC comparison of reconstructed ${m_{\mathrm {r}}}$ for events passing full type-1 $\mu$+jets selection criteria. The MC signal and background show their nominal, pre-fit predictions, and the MC uncertainty pictured in the hatched bands represents statistical errors only. Contribution from QCD multijet background is estimated using the data-driven method described in Section 5. The lower panel shows the ratio of the observed data and total prediction in each bin. |
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Figure 3-f:
Data/MC comparison of reconstructed ${m_{\mathrm {r}}}$ for events passing full type-1 e+jets selection criteria. The MC signal and background show their nominal, pre-fit predictions, and the MC uncertainty pictured in the hatched bands represents statistical errors only. Contribution from QCD multijet background is estimated using the data-driven method described in Section 5. The lower panel shows the ratio of the observed data and total prediction in each bin. |
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Figure 4:
Data/MC comparison of reconstructed ${c^{*}_{\mathrm {r}}}$ (top), $ {| {x_{\mathrm {r}}} |}$ (middle), and ${m_{\mathrm {r}}}$ (bottom) for events passing full type-2 $\mu$+jets (left column) and e+jets (right column) selection criteria. The MC signal and background show their nominal, pre-fit predictions, and the MC uncertainty pictured in the hatched bands represents statistical errors only. Contribution from QCD multijet background is estimated using the data-driven method described in Section 5. The lower panels of each figure show the ratio of the observed data and total prediction in each bin. |
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Figure 4-a:
Data/MC comparison of reconstructed ${c^{*}_{\mathrm {r}}}$ for events passing full type-2 $\mu$+jets selection criteria. The MC signal and background show their nominal, pre-fit predictions, and the MC uncertainty pictured in the hatched bands represents statistical errors only. Contribution from QCD multijet background is estimated using the data-driven method described in Section 5. The lower panel shows the ratio of the observed data and total prediction in each bin. |
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Figure 4-b:
Data/MC comparison of reconstructed ${c^{*}_{\mathrm {r}}}$ for events passing full type-2 e+jets selection criteria. The MC signal and background show their nominal, pre-fit predictions, and the MC uncertainty pictured in the hatched bands represents statistical errors only. Contribution from QCD multijet background is estimated using the data-driven method described in Section 5. The lower panel shows the ratio of the observed data and total prediction in each bin. |
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Figure 4-c:
Data/MC comparison of reconstructed $ {| {x_{\mathrm {r}}} |}$ for events passing full type-2 $\mu$+jets selection criteria. The MC signal and background show their nominal, pre-fit predictions, and the MC uncertainty pictured in the hatched bands represents statistical errors only. Contribution from QCD multijet background is estimated using the data-driven method described in Section 5. The lower panel shows the ratio of the observed data and total prediction in each bin. |
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Figure 4-d:
Data/MC comparison of reconstructed $ {| {x_{\mathrm {r}}} |}$ for events passing full type-2 e+jets selection criteria. The MC signal and background show their nominal, pre-fit predictions, and the MC uncertainty pictured in the hatched bands represents statistical errors only. Contribution from QCD multijet background is estimated using the data-driven method described in Section 5. The lower panel shows the ratio of the observed data and total prediction in each bin. |
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Figure 4-e:
Data/MC comparison of reconstructed ${m_{\mathrm {r}}}$ for events passing full type-2 $\mu$+jets selection criteria. The MC signal and background show their nominal, pre-fit predictions, and the MC uncertainty pictured in the hatched bands represents statistical errors only. Contribution from QCD multijet background is estimated using the data-driven method described in Section 5. The lower panel shows the ratio of the observed data and total prediction in each bin. |
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Figure 4-f:
Data/MC comparison of reconstructed ${m_{\mathrm {r}}}$ for events passing full type-2 e+jets selection criteria. The MC signal and background show their nominal, pre-fit predictions, and the MC uncertainty pictured in the hatched bands represents statistical errors only. Contribution from QCD multijet background is estimated using the data-driven method described in Section 5. The lower panel shows the ratio of the observed data and total prediction in each bin. |
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Figure 5:
Data/MC comparison of reconstructed ${c^{*}_{\mathrm {r}}}$ (top), $ {| {x_{\mathrm {r}}} |}$ (middle), and ${m_{\mathrm {r}}}$ (bottom) for events passing full type-3 $\mu$+jets (left column) and e+jets (right column) selection criteria. The MC signal and background show their nominal, pre-fit predictions, and the MC uncertainty pictured in the hatched bands represents statistical errors only. Contribution from QCD multijet background is estimated using the data-driven method described in Section 5. The lower panels of each figure show the ratio of the observed data and total prediction in each bin. |
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Figure 5-a:
Data/MC comparison of reconstructed ${c^{*}_{\mathrm {r}}}$ for events passing full type-3 $\mu$+jets selection criteria. The MC signal and background show their nominal, pre-fit predictions, and the MC uncertainty pictured in the hatched bands represents statistical errors only. Contribution from QCD multijet background is estimated using the data-driven method described in Section 5. The lower panel shows the ratio of the observed data and total prediction in each bin. |
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Figure 5-b:
Data/MC comparison of reconstructed ${c^{*}_{\mathrm {r}}}$ for events passing full type-3 e+jets selection criteria. The MC signal and background show their nominal, pre-fit predictions, and the MC uncertainty pictured in the hatched bands represents statistical errors only. Contribution from QCD multijet background is estimated using the data-driven method described in Section 5. The lower panel shows the ratio of the observed data and total prediction in each bin. |
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Figure 5-c:
Data/MC comparison of reconstructed $ {| {x_{\mathrm {r}}} |}$ for events passing full type-3 $\mu$+jets selection criteria. The MC signal and background show their nominal, pre-fit predictions, and the MC uncertainty pictured in the hatched bands represents statistical errors only. Contribution from QCD multijet background is estimated using the data-driven method described in Section 5. The lower panel shows the ratio of the observed data and total prediction in each bin. |
png pdf |
Figure 5-d:
Data/MC comparison of reconstructed $ {| {x_{\mathrm {r}}} |}$ for events passing full type-3 e+jets selection criteria. The MC signal and background show their nominal, pre-fit predictions, and the MC uncertainty pictured in the hatched bands represents statistical errors only. Contribution from QCD multijet background is estimated using the data-driven method described in Section 5. The lower panel shows the ratio of the observed data and total prediction in each bin. |
png pdf |
Figure 5-e:
Data/MC comparison of reconstructed ${m_{\mathrm {r}}}$ for events passing full type-3 $\mu$+jets selection criteria. The MC signal and background show their nominal, pre-fit predictions, and the MC uncertainty pictured in the hatched bands represents statistical errors only. Contribution from QCD multijet background is estimated using the data-driven method described in Section 5. The lower panel shows the ratio of the observed data and total prediction in each bin. |
png pdf |
Figure 5-f:
Data/MC comparison of reconstructed ${m_{\mathrm {r}}}$ for events passing full type-3 e+jets selection criteria. The MC signal and background show their nominal, pre-fit predictions, and the MC uncertainty pictured in the hatched bands represents statistical errors only. Contribution from QCD multijet background is estimated using the data-driven method described in Section 5. The lower panel shows the ratio of the observed data and total prediction in each bin. |
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Figure 6:
Neyman constructions for the ${A^{(1)}_\mathrm {FB}}$ (top), $d$ (bottom left) and $\mu $ (bottom right) parameters of interest considering groups of 1,000 toys generated with systematic uncertainty nuisance parameters floating. The horizontal red lines indicate the values of the parameters determined by the fits and the vertical red lines indicate where these values intersect with the central value and uncertainty curves from the toy groups. |
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Figure 6-a:
Neyman construction for the ${A^{(1)}_\mathrm {FB}}$ parameter of interest considering groups of 1,000 toys generated with systematic uncertainty nuisance parameters floating. The horizontal red line indicates the value of the parameter determined by the fit and the vertical red lines indicate where this value intersects with the central value and uncertainty curves from the toy groups. |
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Figure 6-b:
Neyman construction for the $d$ parameter of interest considering groups of 1,000 toys generated with systematic uncertainty nuisance parameters floating. The horizontal red line indicates the value of the parameter determined by the fit and the vertical red lines indicate where this value intersects with the central value and uncertainty curves from the toy groups. |
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Figure 6-c:
Neyman construction for the $\mu $ parameter of interest considering groups of 1,000 toys generated with systematic uncertainty nuisance parameters floating. The horizontal red line indicates the value of the parameter determined by the fit and the vertical red lines indicate where this value intersects with the central value and uncertainty curves from the toy groups. |
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Figure 7:
Postfit data/MC comparisons as functions of template bin number for the ${A^{(1)}_\mathrm {FB}}$ parameter investigation. The top four plots show events in the type-1 (top row) and type-2 (second row) $\mu$+jets (left column) and e+jets (right column) channels, and the bottom two plots show events in the type-3 $\mu$+jets (third row) and e+jets (bottom row) channels, summed over lepton charge in all cases. |
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Figure 7-a:
Postfit data/MC comparison as functions of template bin number for the ${A^{(1)}_\mathrm {FB}}$ parameter investigation for events in the type-1 $\mu$+jets channel, summed over lepton charge. |
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Figure 7-b:
Postfit data/MC comparison as functions of template bin number for the ${A^{(1)}_\mathrm {FB}}$ parameter investigation for events in the type-1 e+jets channel, summed over lepton charge. |
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Figure 7-c:
Postfit data/MC comparison as functions of template bin number for the ${A^{(1)}_\mathrm {FB}}$ parameter investigation for events in the type-2 $\mu$+jets channel, summed over lepton charge. |
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Figure 7-d:
Postfit data/MC comparison as functions of template bin number for the ${A^{(1)}_\mathrm {FB}}$ parameter investigation for events in the type-2 e+jets channel, summed over lepton charge. |
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Figure 7-e:
Postfit data/MC comparison as functions of template bin number for the ${A^{(1)}_\mathrm {FB}}$ parameter investigation for events in the type-3 $\mu$+jets channel, summed over lepton charge. |
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Figure 7-f:
Postfit data/MC comparison as functions of template bin number for the ${A^{(1)}_\mathrm {FB}}$ parameter investigation for events in the type-3 e+jets channel, summed over lepton charge. |
| Tables | |
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Table 1:
List of nuisance parameters considered in fits to data. "N" stands for "normalization" and "S" for "shape" in the "type" column. The "Scale" column lists the absolute value of the associated fractional up/down shifts averaged over all affected template bins. $R_{\text {QCD}}^{t/C/R}$ indicated that the QCD multijet yield uncertainties are independent in each topology $t$, channel $C$, and region $R$. |
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Table 2:
Observed $p$-values representing channel-dependent goodness of fit. |
| Summary |
| The linearized parton-level top quark forward-backward asymmetry ${A^{(1)}_\mathrm{FB}}$ and anomalous chromoelectric ($d$) and chromomagnetic ($\mu$) moments have been measured in 35.9 fb$^{-1}$ of LHC proton-proton collision data collected with the CMS detector in 2016 at a center-of-mass energy of 13 TeV. Candidate $\mathrm{t\bar{t}}$ events decaying to lepton plus jets final states with "resolved" (low-momentum) and "boosted" (high-momentum) topologies were selected and their top quark candidate pairs were reconstructed using a kinematic fit of the decay products to $\mathrm{t\bar{t}}$ hypotheses. Parameters of interest have been measured using template-based likelihood fits to observed data of differential models based on extensions to tree-level cross sections for quark-antiquark and gluon-gluon initial states, and are determined to be ${A^{(1)}_\mathrm{FB}}= $ 0.048$^{+0.088}_{-0.084}$ (stat) $\pm$ 0.028 (syst), $d=$ 0.002 $\pm$ 0.010 (stat) $^{+0.014}_{-0.019}$ (syst), and $\mu=-$0.024 $^{+0.013}_{-0.007}$ (stat) $^{+0.016}_{-0.006}$ (syst). |
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