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| CMS-PAS-TOP-20-008 | ||
| A profile likelihood approach to measure the top quark mass in the lepton+jets channel at $\sqrt{s}= $ 13 TeV | ||
| CMS Collaboration | ||
| April 2022 | ||
| Abstract: The mass of the top quark is measured in 36 fb$^{-1}$ of LHC proton-proton collision data collected with the CMS detector at $\sqrt{s}= $ 13 TeV. The measurement uses a sample of $\mathrm{t\bar{t}}$ events containing one isolated muon or electron and at least four jets in the final state. For each event, the mass is reconstructed from a kinematic fit of the decay products to a $\mathrm{t\bar{t}}$ hypothesis. A profile likelihood method is applied to up to five observables to extract the top quark mass. The impact of systematic uncertainty sources is reduced by including their effect as nuisance parameters in the likelihood. The top quark mass is measured to be 171.77 $\pm$ 0.38 GeV. | ||
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Links:
CDS record (PDF) ;
Physics Briefing ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, EPJC 83 (2023) 963. The superseded preliminary plots can be found here. |
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| Figures | |
png pdf |
Figure 1:
The top quark mass distribution before (left) and after (right) the $ {P_\text {gof}} \ge $ 0.2 selection and the kinematic fit. For the simulated $\mathrm{t\bar{t}}$ events, the jet-parton assignments are classified as correct, wrong, and unmatched permutations as described in the text. The uncertainty bands contain statistical uncertainties in the simulation, normalization uncertainties due to luminosity and cross-section, and all weight-based uncertainties. A value of $ {m_{\mathrm{t}}^\text {gen}} = $ 172.5 GeV is used in the simulation. |
png pdf |
Figure 1-a:
The top quark mass distribution before (left) and after (right) the $ {P_\text {gof}} \ge $ 0.2 selection and the kinematic fit. For the simulated $\mathrm{t\bar{t}}$ events, the jet-parton assignments are classified as correct, wrong, and unmatched permutations as described in the text. The uncertainty bands contain statistical uncertainties in the simulation, normalization uncertainties due to luminosity and cross-section, and all weight-based uncertainties. A value of $ {m_{\mathrm{t}}^\text {gen}} = $ 172.5 GeV is used in the simulation. |
png pdf |
Figure 1-b:
The top quark mass distribution before (left) and after (right) the $ {P_\text {gof}} \ge $ 0.2 selection and the kinematic fit. For the simulated $\mathrm{t\bar{t}}$ events, the jet-parton assignments are classified as correct, wrong, and unmatched permutations as described in the text. The uncertainty bands contain statistical uncertainties in the simulation, normalization uncertainties due to luminosity and cross-section, and all weight-based uncertainties. A value of $ {m_{\mathrm{t}}^\text {gen}} = $ 172.5 GeV is used in the simulation. |
png pdf |
Figure 2:
The distributions of the reconstructed W boson mass for the $ {P_\text {gof}} \ge $ 0.2 category (left) and of the invariant mass of the lepton and the jet assigned to the semileptonic decaying top quark for the category $ {P_\text {gof}} < $ 0.2 category (right). The uncertainty bands contain statistical uncertainties in the simulation, normalization uncertainties due to luminosity and cross-section, and all weight-based uncertainties. A value of $ {m_{\mathrm{t}}^\text {gen}} = $ 172.5 GeV is used in the simulation. |
png pdf |
Figure 2-a:
The distributions of the reconstructed W boson mass for the $ {P_\text {gof}} \ge $ 0.2 category (left) and of the invariant mass of the lepton and the jet assigned to the semileptonic decaying top quark for the category $ {P_\text {gof}} < $ 0.2 category (right). The uncertainty bands contain statistical uncertainties in the simulation, normalization uncertainties due to luminosity and cross-section, and all weight-based uncertainties. A value of $ {m_{\mathrm{t}}^\text {gen}} = $ 172.5 GeV is used in the simulation. |
png pdf |
Figure 2-b:
The distributions of the reconstructed W boson mass for the $ {P_\text {gof}} \ge $ 0.2 category (left) and of the invariant mass of the lepton and the jet assigned to the semileptonic decaying top quark for the category $ {P_\text {gof}} < $ 0.2 category (right). The uncertainty bands contain statistical uncertainties in the simulation, normalization uncertainties due to luminosity and cross-section, and all weight-based uncertainties. A value of $ {m_{\mathrm{t}}^\text {gen}} = $ 172.5 GeV is used in the simulation. |
png pdf |
Figure 3:
The distributions of $ {m_{\ell \mathrm{b}}^\text {reco}} / {m_{\mathrm{t}}^\text {fit}} $, the invariant mass of the lepton and the jet assigned to the semileptonic decaying top quark divided by the top quark mass form the kinematic fit, (left) and of ${R_{\mathrm{b} \mathrm{q}}^\text {reco}}$, the ratio of the scalar sum of the transverse momenta of the two b-tagged jets, and the two leading untagged jets (right), both for the $ {P_\text {gof}} \ge $ 0.2 category. The uncertainty bands contain statistical uncertainties in the simulation, normalization uncertainties due to luminosity and cross-section, and all weight-based uncertainties. A value of $ {m_{\mathrm{t}}^\text {gen}} = $ 172.5 GeV is used in the simulation. |
png pdf |
Figure 3-a:
The distributions of $ {m_{\ell \mathrm{b}}^\text {reco}} / {m_{\mathrm{t}}^\text {fit}} $, the invariant mass of the lepton and the jet assigned to the semileptonic decaying top quark divided by the top quark mass form the kinematic fit, (left) and of ${R_{\mathrm{b} \mathrm{q}}^\text {reco}}$, the ratio of the scalar sum of the transverse momenta of the two b-tagged jets, and the two leading untagged jets (right), both for the $ {P_\text {gof}} \ge $ 0.2 category. The uncertainty bands contain statistical uncertainties in the simulation, normalization uncertainties due to luminosity and cross-section, and all weight-based uncertainties. A value of $ {m_{\mathrm{t}}^\text {gen}} = $ 172.5 GeV is used in the simulation. |
png pdf |
Figure 3-b:
The distributions of $ {m_{\ell \mathrm{b}}^\text {reco}} / {m_{\mathrm{t}}^\text {fit}} $, the invariant mass of the lepton and the jet assigned to the semileptonic decaying top quark divided by the top quark mass form the kinematic fit, (left) and of ${R_{\mathrm{b} \mathrm{q}}^\text {reco}}$, the ratio of the scalar sum of the transverse momenta of the two b-tagged jets, and the two leading untagged jets (right), both for the $ {P_\text {gof}} \ge $ 0.2 category. The uncertainty bands contain statistical uncertainties in the simulation, normalization uncertainties due to luminosity and cross-section, and all weight-based uncertainties. A value of $ {m_{\mathrm{t}}^\text {gen}} = $ 172.5 GeV is used in the simulation. |
png pdf |
Figure 4:
Left: Comparison of the expected total uncertainty on ${m_{\mathrm{t}}}$ in the combined lepton+jets channel and for the different observable-category sets defined in Table 1. Right: The difference between the measured and generated ${m_{\mathrm{t}}}$ values divided by the uncertainty reported by the fit from pseudo-experiments without (red) or with (blue) the statistical nuisance parameters ${\hat{\beta}}$ and ${\hat{\omega}}$ in the ML fit. The $\mu $ and $\sigma $ parameters of Gaussian functions (red and blue lines) fit to the histograms are included in the legend. |
png pdf |
Figure 4-a:
Left: Comparison of the expected total uncertainty on ${m_{\mathrm{t}}}$ in the combined lepton+jets channel and for the different observable-category sets defined in Table 1. Right: The difference between the measured and generated ${m_{\mathrm{t}}}$ values divided by the uncertainty reported by the fit from pseudo-experiments without (red) or with (blue) the statistical nuisance parameters ${\hat{\beta}}$ and ${\hat{\omega}}$ in the ML fit. The $\mu $ and $\sigma $ parameters of Gaussian functions (red and blue lines) fit to the histograms are included in the legend. |
png pdf |
Figure 4-b:
Left: Comparison of the expected total uncertainty on ${m_{\mathrm{t}}}$ in the combined lepton+jets channel and for the different observable-category sets defined in Table 1. Right: The difference between the measured and generated ${m_{\mathrm{t}}}$ values divided by the uncertainty reported by the fit from pseudo-experiments without (red) or with (blue) the statistical nuisance parameters ${\hat{\beta}}$ and ${\hat{\omega}}$ in the ML fit. The $\mu $ and $\sigma $ parameters of Gaussian functions (red and blue lines) fit to the histograms are included in the legend. |
png pdf |
Figure 5:
Left: Measurement of ${m_{\mathrm{t}}}$ in the the three different channels for the different sets of observables and categories. Right: Dependence of the 5D result on the assumed correlation between the FSR PS scales per branching in the lepton + jets channel. |
png pdf |
Figure 5-a:
Left: Measurement of ${m_{\mathrm{t}}}$ in the the three different channels for the different sets of observables and categories. Right: Dependence of the 5D result on the assumed correlation between the FSR PS scales per branching in the lepton + jets channel. |
png pdf |
Figure 5-b:
Left: Measurement of ${m_{\mathrm{t}}}$ in the the three different channels for the different sets of observables and categories. Right: Dependence of the 5D result on the assumed correlation between the FSR PS scales per branching in the lepton + jets channel. |
png pdf |
Figure 6:
Distribution of ${m_{\mathrm{t}}^\text {fit}}$ (top) and the additional observables (bottom) that are the input to the ML fit and their post-fit probability density functions. The green and yellow bands represent the 1-sigma and 2-sigma error bands. |
png pdf |
Figure 6-a:
Distribution of ${m_{\mathrm{t}}^\text {fit}}$ (top) and the additional observables (bottom) that are the input to the ML fit and their post-fit probability density functions. The green and yellow bands represent the 1-sigma and 2-sigma error bands. |
png pdf |
Figure 6-b:
Distribution of ${m_{\mathrm{t}}^\text {fit}}$ (top) and the additional observables (bottom) that are the input to the ML fit and their post-fit probability density functions. The green and yellow bands represent the 1-sigma and 2-sigma error bands. |
png pdf |
Figure 7:
Measurement of ${m_{\mathrm{t}}}$ in the combined lepton+jets channel using the 5D set of observables and categories. The left plot shows the post-fit pulls on the most important nuisance parameters and the numbers quote the post-fit uncertainty on the nuisance parameter. The right plot shows their pre-fit and post-fit impacts. The post-fit impacts include the contribution from the nuisance parameters accounting for the limited size of simulation samples (MC stat.). The average of these post-fit impacts is printed on the right. The rows are sorted by the size of the post-fit impact. |
| Tables | |
png pdf |
Table 1:
The overall list of different input histograms and their inclusion in a certain histogram set. A histogram marked with "x" is included in a set (measurement). |
| Summary |
| The mass of the top quark is measured in 36 fb$^{-1}$ of LHC proton-proton collision data collected with the CMS detector at $ \sqrt{s} = $ 13 TeV. The measurement uses a sample of $\mathrm{t\bar{t}}$ events containing one isolated muon or electron and at least four jets in the final state. For each event the mass is reconstructed from a kinematic fit of the decay products to a $\mathrm{t\bar{t}}$ hypothesis. A likelihood method is applied to up to five observables to extract the top quark mass and constrain the influence of systematic effects which are included as nuisance parameters in the likelihood. Consistent results are obtained for measurements with different sets of observables and the top quark mass is measured to be 171.77 $\pm$ 0.38 GeV, including 0.04 GeV statistical uncertainty. This result denotes a considerable improvement compared to all previously published top quark mass measurements and supersedes the previously published measurement in this channel on the same data set. |
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