CMSTOP17004 ; CERNEP2019119  
Measurement of the top quark Yukawa coupling from $\mathrm{t\bar{t}}$ kinematic distributions in the lepton+jets final state in protonproton collisions at $\sqrt{s} = $ 13 TeV  
CMS Collaboration  
2 July 2019  
Phys. Rev. D 100 (2019) 072007  
Abstract: Results are presented for an extraction of the top quark Yukawa coupling from top quarkantiquark ($\mathrm{t\bar{t}}$) kinematic distributions in the lepton plus jets final state in protonproton collisions, based on data collected by the CMS experiment at the LHC at $\sqrt{s} = $ 13 TeV, corresponding to an integrated luminosity of 35.8 fb$^{1}$. Corrections from weak boson exchange, including Higgs bosons, between the top quarks can produce large distortions of differential distributions near the energy threshold of $\mathrm{t\bar{t}}$ production. Therefore, precise measurements of these distributions are sensitive to the Yukawa coupling. Top quark events are reconstructed with at least three jets in the final state, and a novel technique is introduced to reconstruct the $\mathrm{t\bar{t}}$ system for events with one missing jet. This technique enhances the experimental sensitivity in the low invariant mass region, ${M_{\mathrm{t\bar{t}}}} $. The data yields in ${M_{\mathrm{t\bar{t}}}} $, the rapidity difference ${y_{\mathrm{t}}y_{\mathrm{\bar{t}}}}$, and the number of reconstructed jets are compared with distributions representing different Yukawa couplings. These comparisons are used to measure the ratio of the top quark Yukawa coupling to its standard model predicted value to be 1.07$^{+0.34}_{0.43}$ with an upper limit of 1.67 at the 95% confidence level.  
Links: eprint arXiv:1907.01590 [hepex] (PDF) ; CDS record ; inSPIRE record ; CADI line (restricted) ; 
Figures  
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Figure 1:
Example of Feynman diagrams for gluon and ${\mathrm{q} \mathrm{\bar{q}}}$induced processes of ${\mathrm{t} {}\mathrm{\bar{t}}}$ production and the virtual corrections. The symbol $\Gamma $ stands for all contributions from gauge and Higgs boson exchanges. 
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Figure 1a:
Example of Feynman diagram for gluoninduced processes of ${\mathrm{t} {}\mathrm{\bar{t}}}$ production and the virtual corrections. The symbol $\Gamma $ stands for all contributions from gauge and Higgs boson exchanges. 
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Figure 1b:
Example of Feynman diagram for ${\mathrm{q} \mathrm{\bar{q}}}$induced processes of ${\mathrm{t} {}\mathrm{\bar{t}}}$ production and the virtual corrections. The symbol $\Gamma $ stands for all contributions from gauge and Higgs boson exchanges. 
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Figure 2:
The dependence of the ratio of weak force corrections over the LO QCD production cross section as calculated by Hathor on the sensitive kinematic variables ${M_{{\mathrm{t} {}\mathrm{\bar{t}}}}}$ and ${\Delta y_{{\mathrm{t} {}\mathrm{\bar{t}}}}}$ at the generator level for different values of ${Y_{\mathrm{t}}} $. The lines contain an uncertainty band (generally not visible) derived from the dependence of the weak correction on the top quark mass varied by $\pm $1 GeV. 
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Figure 2a:
The dependence of the ratio of weak force corrections over the LO QCD production cross section as calculated by Hathor on the sensitive kinematic variable ${M_{{\mathrm{t} {}\mathrm{\bar{t}}}}}$ at the generator level for different values of ${Y_{\mathrm{t}}} $. The lines contain an uncertainty band (generally not visible) derived from the dependence of the weak correction on the top quark mass varied by $\pm $1 GeV. 
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Figure 2b:
The dependence of the ratio of weak force corrections over the LO QCD production cross section as calculated by Hathor on the sensitive kinematic variable ${\Delta y_{{\mathrm{t} {}\mathrm{\bar{t}}}}}$ at the generator level for different values of ${Y_{\mathrm{t}}} $. The lines contain an uncertainty band (generally not visible) derived from the dependence of the weak correction on the top quark mass varied by $\pm $1 GeV. 
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Figure 3:
Threejet reconstruction. Distributions of the distance ${D_{\nu,\mathrm {min}}}$ for correctly and wrongly selected ${\mathrm{b} _\ell}$ candidates (left). Mass distribution of the correctly and wrongly selected ${\mathrm{b} _\mathrm {h}}$ and the jet from the W boson (middle). Distribution of the negative combined loglikelihood (right). All distributions are normalized to have unit area. 
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Figure 3a:
Threejet reconstruction. Distributions of the distance ${D_{\nu,\mathrm {min}}}$ for correctly and wrongly selected. All distributions are normalized to have unit area. 
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Figure 3b:
Threejet reconstruction. Distributions of the distance ${D_{\nu,\mathrm {min}}}$ for correctly and wrongly selected ${\mathrm{b} _\ell}$ candidates. All distributions are normalized to have unit area. 
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Figure 3c:
Threejet reconstruction. Distribution of the negative combined loglikelihood. All distributions are normalized to have unit area. 
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Figure 4:
Relative difference between the reconstructed and generated ${M_{{\mathrm{t} {}\mathrm{\bar{t}}}}}$ (left) and ${\Delta y_{{\mathrm{t} {}\mathrm{\bar{t}}}}}$ (right) for threejet and fourjet event categories. 
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Figure 4a:
Relative difference between the reconstructed and generated ${M_{{\mathrm{t} {}\mathrm{\bar{t}}}}}$ for threejet and fourjet event categories. 
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Figure 4b:
Relative difference between the reconstructed and generated ${\Delta y_{{\mathrm{t} {}\mathrm{\bar{t}}}}}$ for threejet and fourjet event categories. 
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Figure 5:
Threejet events after selection and ${\mathrm{t} {}\mathrm{\bar{t}}}$ reconstruction. The plots show (left to right, upper to lower) the missing transverse momentum (${{p_{\mathrm {T}}} ^\text {miss}}$), the lepton pseudorapidity, and $ {p_{\mathrm {T}}} $ and the absolute rapidity of the top quark decaying hadronically, semileptonically, and of the ${\mathrm{t} {}\mathrm{\bar{t}}}$ system. The hatched band shows the total uncertainty associated with the signal and background predictions with the individual sources of uncertainty assumed to be uncorrelated. The ratios of data to the sum of the predicted yields are provided at the bottom of each panel. 
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Figure 5a:
Threejet events after selection and ${\mathrm{t} {}\mathrm{\bar{t}}}$ reconstruction. The plot shows the missing transverse momentum (${{p_{\mathrm {T}}} ^\text {miss}}$). The hatched band shows the total uncertainty associated with the signal and background predictions with the individual sources of uncertainty assumed to be uncorrelated. The ratios of data to the sum of the predicted yields are provided at the bottom of the panel. 
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Figure 5b:
Threejet events after selection and ${\mathrm{t} {}\mathrm{\bar{t}}}$ reconstruction. The plot shows the lepton pseudorapidity. The hatched band shows the total uncertainty associated with the signal and background predictions with the individual sources of uncertainty assumed to be uncorrelated. The ratios of data to the sum of the predicted yields are provided at the bottom of the panel. 
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Figure 5c:
Threejet events after selection and ${\mathrm{t} {}\mathrm{\bar{t}}}$ reconstruction. The plot shows the $ {p_{\mathrm {T}}} $ of the top quark decaying hadronically. The hatched band shows the total uncertainty associated with the signal and background predictions with the individual sources of uncertainty assumed to be uncorrelated. The ratios of data to the sum of the predicted yields are provided at the bottom of the panel. 
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Figure 5d:
Threejet events after selection and ${\mathrm{t} {}\mathrm{\bar{t}}}$ reconstruction. The plot shows the absolute rapidity of the top quark decaying hadronically. The hatched band shows the total uncertainty associated with the signal and background predictions with the individual sources of uncertainty assumed to be uncorrelated. The ratios of data to the sum of the predicted yields are provided at the bottom of the panel. 
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Figure 5e:
Threejet events after selection and ${\mathrm{t} {}\mathrm{\bar{t}}}$ reconstruction. The plot shows the $ {p_{\mathrm {T}}} $ of the top quark decaying semileptonically. The hatched band shows the total uncertainty associated with the signal and background predictions with the individual sources of uncertainty assumed to be uncorrelated. The ratios of data to the sum of the predicted yields are provided at the bottom of the panel. 
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Figure 5f:
Threejet events after selection and ${\mathrm{t} {}\mathrm{\bar{t}}}$ reconstruction. The plot shows the absolute rapidity of the top quark decaying semileptonically. The hatched band shows the total uncertainty associated with the signal and background predictions with the individual sources of uncertainty assumed to be uncorrelated. The ratios of data to the sum of the predicted yields are provided at the bottom of the panel. 
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Figure 5g:
Threejet events after selection and ${\mathrm{t} {}\mathrm{\bar{t}}}$ reconstruction. The plot shows the $ {p_{\mathrm {T}}} $ of the ${\mathrm{t} {}\mathrm{\bar{t}}}$ system. The hatched band shows the total uncertainty associated with the signal and background predictions with the individual sources of uncertainty assumed to be uncorrelated. The ratios of data to the sum of the predicted yields are provided at the bottom of the panel. 
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Figure 5h:
Threejet events after selection and ${\mathrm{t} {}\mathrm{\bar{t}}}$ reconstruction. The plot shows the absolute rapidity of the ${\mathrm{t} {}\mathrm{\bar{t}}}$ system. The hatched band shows the total uncertainty associated with the signal and background predictions with the individual sources of uncertainty assumed to be uncorrelated. The ratios of data to the sum of the predicted yields are provided at the bottom of the panel. 
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Figure 6:
Fourjet events after selection and ${\mathrm{t} {}\mathrm{\bar{t}}}$ reconstruction. Same distributions as described in Fig. 5. 
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Figure 6a:
Fourjet events after selection and ${\mathrm{t} {}\mathrm{\bar{t}}}$ reconstruction. Same distributions as described in Fig. 5. 
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Figure 6b:
Fourjet events after selection and ${\mathrm{t} {}\mathrm{\bar{t}}}$ reconstruction. Same distributions as described in Fig. 5. 
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Figure 6c:
Fourjet events after selection and ${\mathrm{t} {}\mathrm{\bar{t}}}$ reconstruction. Same distributions as described in Fig. 5. 
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Figure 6d:
Fourjet events after selection and ${\mathrm{t} {}\mathrm{\bar{t}}}$ reconstruction. Same distributions as described in Fig. 5. 
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Figure 6e:
Fourjet events after selection and ${\mathrm{t} {}\mathrm{\bar{t}}}$ reconstruction. Same distributions as described in Fig. 5. 
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Figure 6f:
Fourjet events after selection and ${\mathrm{t} {}\mathrm{\bar{t}}}$ reconstruction. Same distributions as described in Fig. 5. 
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Figure 6g:
Fourjet events after selection and ${\mathrm{t} {}\mathrm{\bar{t}}}$ reconstruction. Same distributions as described in Fig. 5. 
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Figure 6h:
Fourjet events after selection and ${\mathrm{t} {}\mathrm{\bar{t}}}$ reconstruction. Same distributions as described in Fig. 5. 
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Figure 7:
Events with five or more jets after selection and ${\mathrm{t} {}\mathrm{\bar{t}}}$ reconstruction. Same distributions as described in Fig. 5. 
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Figure 7a:
Events with five or more jets after selection and ${\mathrm{t} {}\mathrm{\bar{t}}}$ reconstruction. Same distributions as described in Fig. 5. 
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Figure 7b:
Events with five or more jets after selection and ${\mathrm{t} {}\mathrm{\bar{t}}}$ reconstruction. Same distributions as described in Fig. 5. 
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Figure 7c:
Events with five or more jets after selection and ${\mathrm{t} {}\mathrm{\bar{t}}}$ reconstruction. Same distributions as described in Fig. 5. 
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Figure 7d:
Events with five or more jets after selection and ${\mathrm{t} {}\mathrm{\bar{t}}}$ reconstruction. Same distributions as described in Fig. 5. 
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Figure 7e:
Events with five or more jets after selection and ${\mathrm{t} {}\mathrm{\bar{t}}}$ reconstruction. Same distributions as described in Fig. 5. 
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Figure 7f:
Events with five or more jets after selection and ${\mathrm{t} {}\mathrm{\bar{t}}}$ reconstruction. Same distributions as described in Fig. 5. 
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Figure 7g:
Events with five or more jets after selection and ${\mathrm{t} {}\mathrm{\bar{t}}}$ reconstruction. Same distributions as described in Fig. 5. 
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Figure 7h:
Events with five or more jets after selection and ${\mathrm{t} {}\mathrm{\bar{t}}}$ reconstruction. Same distributions as described in Fig. 5. 
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Figure 8:
The strength of the weak interaction correction, relative to the predicted POWHEG signal, $R^\mathrm {bin}$, as a function of ${Y_{\mathrm{t}}} $ in the threejet category. The plots correspond to the first eight ${M_{{\mathrm{t} {}\mathrm{\bar{t}}}}}$ bins for $ { {\Delta y_{{\mathrm{t} {}\mathrm{\bar{t}}}}} } < $ 0.6 (as shown in Fig. 10). A quadratic fit is performed in each bin. 
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Figure 8a:
The strength of the weak interaction correction, relative to the predicted POWHEG signal, $R^\mathrm {bin}$, as a function of ${Y_{\mathrm{t}}} $ in the threejet category. The plot corresponds to ${M_{{\mathrm{t} {}\mathrm{\bar{t}}}}}$ bin 1 for $ { {\Delta y_{{\mathrm{t} {}\mathrm{\bar{t}}}}} } < $ 0.6 (as shown in Fig. 10). A quadratic fit is performed in the bin. 
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Figure 8b:
The strength of the weak interaction correction, relative to the predicted POWHEG signal, $R^\mathrm {bin}$, as a function of ${Y_{\mathrm{t}}} $ in the threejet category. The plot corresponds to ${M_{{\mathrm{t} {}\mathrm{\bar{t}}}}}$ bin 2 for $ { {\Delta y_{{\mathrm{t} {}\mathrm{\bar{t}}}}} } < $ 0.6 (as shown in Fig. 10). A quadratic fit is performed in the bin. 
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Figure 8c:
The strength of the weak interaction correction, relative to the predicted POWHEG signal, $R^\mathrm {bin}$, as a function of ${Y_{\mathrm{t}}} $ in the threejet category. The plot corresponds to ${M_{{\mathrm{t} {}\mathrm{\bar{t}}}}}$ bin 3 for $ { {\Delta y_{{\mathrm{t} {}\mathrm{\bar{t}}}}} } < $ 0.6 (as shown in Fig. 10). A quadratic fit is performed in the bin. 
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Figure 8d:
The strength of the weak interaction correction, relative to the predicted POWHEG signal, $R^\mathrm {bin}$, as a function of ${Y_{\mathrm{t}}} $ in the threejet category. The plot corresponds to ${M_{{\mathrm{t} {}\mathrm{\bar{t}}}}}$ bin 4 for $ { {\Delta y_{{\mathrm{t} {}\mathrm{\bar{t}}}}} } < $ 0.6 (as shown in Fig. 10). A quadratic fit is performed in the bin. 
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Figure 8e:
The strength of the weak interaction correction, relative to the predicted POWHEG signal, $R^\mathrm {bin}$, as a function of ${Y_{\mathrm{t}}} $ in the threejet category. The plot corresponds to ${M_{{\mathrm{t} {}\mathrm{\bar{t}}}}}$ bin 5 for $ { {\Delta y_{{\mathrm{t} {}\mathrm{\bar{t}}}}} } < $ 0.6 (as shown in Fig. 10). A quadratic fit is performed in the bin. 
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Figure 8f:
The strength of the weak interaction correction, relative to the predicted POWHEG signal, $R^\mathrm {bin}$, as a function of ${Y_{\mathrm{t}}} $ in the threejet category. The plot corresponds to ${M_{{\mathrm{t} {}\mathrm{\bar{t}}}}}$ bin 6 for $ { {\Delta y_{{\mathrm{t} {}\mathrm{\bar{t}}}}} } < $ 0.6 (as shown in Fig. 10). A quadratic fit is performed in the bin. 
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Figure 8g:
The strength of the weak interaction correction, relative to the predicted POWHEG signal, $R^\mathrm {bin}$, as a function of ${Y_{\mathrm{t}}} $ in the threejet category. The plot corresponds to ${M_{{\mathrm{t} {}\mathrm{\bar{t}}}}}$ bin 7 for $ { {\Delta y_{{\mathrm{t} {}\mathrm{\bar{t}}}}} } < $ 0.6 (as shown in Fig. 10). A quadratic fit is performed in the bin. 
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Figure 8h:
The strength of the weak interaction correction, relative to the predicted POWHEG signal, $R^\mathrm {bin}$, as a function of ${Y_{\mathrm{t}}} $ in the threejet category. The plot corresponds to ${M_{{\mathrm{t} {}\mathrm{\bar{t}}}}}$ bin 8 for $ { {\Delta y_{{\mathrm{t} {}\mathrm{\bar{t}}}}} } < $ 0.6 (as shown in Fig. 10). A quadratic fit is performed in the bin. 
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Figure 9:
The strength of the weak interaction correction, relative to the predicted POWHEG signal, $R^\mathrm {bin}$, as a function of ${Y_{\mathrm{t}}} $ in the categories with four and five or more jets. The plots correspond to the first six ${M_{{\mathrm{t} {}\mathrm{\bar{t}}}}}$ bins for $ { {\Delta y_{{\mathrm{t} {}\mathrm{\bar{t}}}}} } < $ 0.6 (as shown in Fig. 8). A quadratic fit is performed in each bin. 
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Figure 9a:
The strength of the weak interaction correction, relative to the predicted POWHEG signal, $R^\mathrm {bin}$, as a function of ${Y_{\mathrm{t}}} $ in the categories with four and five or more jets. The plot corresponds to ${M_{{\mathrm{t} {}\mathrm{\bar{t}}}}}$ bin 1 for $ { {\Delta y_{{\mathrm{t} {}\mathrm{\bar{t}}}}} } < $ 0.6 (as shown in Fig. 8). A quadratic fit is performed in the bin. 
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Figure 9b:
The strength of the weak interaction correction, relative to the predicted POWHEG signal, $R^\mathrm {bin}$, as a function of ${Y_{\mathrm{t}}} $ in the categories with four and five or more jets. The plot corresponds to ${M_{{\mathrm{t} {}\mathrm{\bar{t}}}}}$ bin 2 for $ { {\Delta y_{{\mathrm{t} {}\mathrm{\bar{t}}}}} } < $ 0.6 (as shown in Fig. 8). A quadratic fit is performed in the bin. 
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Figure 9c:
The strength of the weak interaction correction, relative to the predicted POWHEG signal, $R^\mathrm {bin}$, as a function of ${Y_{\mathrm{t}}} $ in the categories with four and five or more jets. The plot corresponds to ${M_{{\mathrm{t} {}\mathrm{\bar{t}}}}}$ bin 3 for $ { {\Delta y_{{\mathrm{t} {}\mathrm{\bar{t}}}}} } < $ 0.6 (as shown in Fig. 8). A quadratic fit is performed in the bin. 
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Figure 9d:
The strength of the weak interaction correction, relative to the predicted POWHEG signal, $R^\mathrm {bin}$, as a function of ${Y_{\mathrm{t}}} $ in the categories with four and five or more jets. The plot corresponds to ${M_{{\mathrm{t} {}\mathrm{\bar{t}}}}}$ bin 4 for $ { {\Delta y_{{\mathrm{t} {}\mathrm{\bar{t}}}}} } < $ 0.6 (as shown in Fig. 8). A quadratic fit is performed in the bin. 
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Figure 9e:
The strength of the weak interaction correction, relative to the predicted POWHEG signal, $R^\mathrm {bin}$, as a function of ${Y_{\mathrm{t}}} $ in the categories with four and five or more jets. The plot corresponds to ${M_{{\mathrm{t} {}\mathrm{\bar{t}}}}}$ bin 5 for $ { {\Delta y_{{\mathrm{t} {}\mathrm{\bar{t}}}}} } < $ 0.6 (as shown in Fig. 8). A quadratic fit is performed in the bin. 
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Figure 9f:
The strength of the weak interaction correction, relative to the predicted POWHEG signal, $R^\mathrm {bin}$, as a function of ${Y_{\mathrm{t}}} $ in the categories with four and five or more jets. The plot corresponds to ${M_{{\mathrm{t} {}\mathrm{\bar{t}}}}}$ bin 6 for $ { {\Delta y_{{\mathrm{t} {}\mathrm{\bar{t}}}}} } < $ 0.6 (as shown in Fig. 8). A quadratic fit is performed in the bin. 
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Figure 10:
The $ {M_{{\mathrm{t} {}\mathrm{\bar{t}}}}} $ distribution in $ { {\Delta y_{{\mathrm{t} {}\mathrm{\bar{t}}}}} }$ bins for all events combined, after the simultaneous likelihood fit in all jet channels. The hatched bands show the total postfit uncertainty. The ratios of data to the sum of the predicted yields are provided in the lower panel. To show the sensitivity of the data to ${Y_{\mathrm{t}}} = $ 1 and ${Y_{\mathrm{t}}} = $ 2, the prefit yields are shown in the upper panel, and the yield ratio $R^{\mathrm {bin}}({Y_{\mathrm{t}}} =2)/R^{\mathrm {bin}}({Y_{\mathrm{t}}} =1)$ in the lower panel. 
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Figure 11:
The test statistic scan versus ${Y_{\mathrm{t}}} $ for each channel (three, four, and five or more jets), and all channels combined. The test statistic minimum indicates the best fit of ${Y_{\mathrm{t}}} $. The horizontal lines indicate 68 and 95% CL intervals. 
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Figure 11a:
The test statistic scan versus ${Y_{\mathrm{t}}} $ for the channel with three jets. The test statistic minimum indicates the best fit of ${Y_{\mathrm{t}}} $. The horizontal lines indicate 68 and 95% CL intervals. 
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Figure 11b:
The test statistic scan versus ${Y_{\mathrm{t}}} $ for the channel with four jets. The test statistic minimum indicates the best fit of ${Y_{\mathrm{t}}} $. The horizontal lines indicate 68 and 95% CL intervals. 
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Figure 11c:
The test statistic scan versus ${Y_{\mathrm{t}}} $ for the channel with five or more jets. The test statistic minimum indicates the best fit of ${Y_{\mathrm{t}}} $. The horizontal lines indicate 68 and 95% CL intervals. 
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Figure 11d:
The test statistic scan versus ${Y_{\mathrm{t}}} $ for all channels combined. The test statistic minimum indicates the best fit of ${Y_{\mathrm{t}}} $. The horizontal lines indicate 68 and 95% CL intervals. 
Tables  
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Table 1:
Expected and observed yields after event selection and ${\mathrm{t} {}\mathrm{\bar{t}}}$ reconstruction, with statistical uncertainties in the expected yields. The QCD multijet yield is derived from Eq. (3) and its uncertainty is the statistical uncertainty in the control region from the databased QCD multijet determination described in Section 7. 
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Table 2:
Summary of the sources of systematic uncertainty, their effects and magnitudes on signal and backgrounds. If the uncertainty shows a shape dependence in the ${M_{{\mathrm{t} {}\mathrm{\bar{t}}}}}$ and ${\Delta y_{{\mathrm{t} {}\mathrm{\bar{t}}}}}$ distributions, it is treated as such in the likelihood. Only the luminosity, background normalization, and ISR uncertainties are not considered as shape uncertainties. 
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Table 3:
The expected and observed best fit values and 95% CL upper limits on ${Y_{\mathrm{t}}} $. 
Summary 
A measurement of the top quark Yukawa coupling is presented, extracted by investigating $\mathrm{t\bar{t}}$ pair production in final states with an electron or muon and several jets, using protonproton data collected by the CMS experiment at $\sqrt{s} = $ 13 TeV, corresponding to an integrated luminosity of 35.8 fb$^{1}$. The $\mathrm{t\bar{t}}$ production cross section is sensitive to the top quark Yukawa coupling through weak force corrections that can modify the distributions of the mass of top quarkantiquark pairs, ${M_{\mathrm{t\bar{t}}}} $, and the rapidity difference between top quark and antiquark, $\delta Y$. The kinematic properties of these final states are reconstructed in events with at least three jets, two of which are identified as originating from bottom quarks. The inclusion of events with only three reconstructed jets using a dedicated algorithm improves the sensitivity of the analysis by increasing the signal from events in the low${M_{\mathrm{t\bar{t}}}}$ region, which is most sensitive to the Yukawa coupling. The ratio of the top quark Yukawa coupling to its expected SM value, ${Y_{\mathrm{t}}} $, is extracted by comparing the data with the expected $\mathrm{t\bar{t}}$ signal for different values of ${Y_{\mathrm{t}}} $ in a total of 55 bins in ${M_{\mathrm{t\bar{t}}}} $, ${\delta Y}$, and the number of reconstructed jets. The measured value of ${Y_{\mathrm{t}}} $ is 1.07$^{+0.34}_{0.43}$, compared to an expected value of 1.00$^{+0.35}_{0.48}$. The observed upper limit on ${Y_{\mathrm{t}}} $ is 1.67 at 95% confidence level (CL), with an expected value of 1.62. Although the method presented in this paper is not as sensitive as the combined CMS measurement of ${Y_{\mathrm{t}}} $ performed using Higgs boson production and decays in multiple channels [61], it has the advantage that it does not depend on any assumptions about the couplings of the Higgs boson to particles other than the top quark. The result presented here is more sensitive than the only other result from CMS exclusively dependent on ${Y_{\mathrm{t}}} $, namely the limit on the ${\mathrm{t\bar{t}}}{\mathrm{t\bar{t}}}$ cross section, which constrains ${Y_{\mathrm{t}}} $ to be less than 2.1 at 95% CL [8]. 
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