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| CMS-HIN-24-021 ; CERN-EP-2026-066 | ||
| Measurement of the top quark pair production cross section in $ \mathrm{Pb}\mathrm{Pb} $ collisions at$ \sqrt{\smash[b]{s_{_{\mathrm{NN}}}}}= $ 5.36 TeV | ||
| CMS Collaboration | ||
| 29 April 2026 | ||
| Submitted to the Journal of High Energy Physics | ||
| Abstract: The inclusive cross section for top quark pair ( $ \mathrm{t} \overline{\mathrm{t}} $) production in lead-lead ($ \mathrm{Pb}\mathrm{Pb} $) collisions is reported for the first time at a center-of-mass energy per nucleon pair of 5.36 TeV. The analysis uses data corresponding to an integrated luminosity of 1.58$ \text{nb}^{-1}$ collected by the CMS experiment at the CERN LHC in 2023. The $ \mathrm{t} \overline{\mathrm{t}} $ production cross section, $ \sigma_{{\mathrm{t}\overline{\mathrm{t}}} }= $ 3.42 $ ^{+0.54}_{-0.51} $ $ $ (stat) $ ^{+0.50}_{-0.43} $ (syst) $\mu b$, is measured in dilepton final states using a fit to a multivariate discriminator that combines the decay electron and muon kinematic properties with the multiplicity of bottom quark jets. The result is consistent with perturbative quantum chromodynamics calculations at next-to-next-to-leading order (NNLO) accuracy employing several nuclear parton distribution functions. In addition, the Drell--Yan production cross section ($ \sigma_\text{DY} $) for dilepton masses above 10 GeV and the ratio of $ \mathrm{t} \overline{\mathrm{t}} $ to DY cross sections ($ R_{{\mathrm{t}\overline{\mathrm{t}}} /\mathrm{DY}} $) are found to be compatible with the NNLO predictions. The observables $ \sigma_{{\mathrm{t}\overline{\mathrm{t}}} } $, $ \sigma_\text{DY} $, and $ R_{{\mathrm{t}\overline{\mathrm{t}}} /\mathrm{DY}} $ are measured separately for central and semicentral $ \mathrm{Pb}\mathrm{Pb} $ collisions to investigate for the first time the dependence of top quark production on the collision impact parameter. | ||
| Links: e-print arXiv:2604.27091 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Distributions of dilepton $ p_{\mathrm{T}}(\ell\ell) $ (left) and invariant mass $ m(\ell\ell) $ (right) variables in the same-flavor ($ \ell\ell $) channels. The $ m(\ell\ell) $ distribution is shown before applying the veto of the Z boson resonant region. The data (black markers with error bars representing statistical uncertainties) are overlaid on top of the stacked contributions from the expected $ \mathrm{t} \overline{\mathrm{t}} $ (blue), nonprompt (light orange), WW (red), single top quark (gray), and $ \mathrm{DY} $ (violet) processes. The last bin includes the overflow entries. In the left panel, the event counts are divided by the variable bin width. |
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Figure 1-a:
Distributions of dilepton $ p_{\mathrm{T}}(\ell\ell) $ (left) and invariant mass $ m(\ell\ell) $ (right) variables in the same-flavor ($ \ell\ell $) channels. The $ m(\ell\ell) $ distribution is shown before applying the veto of the Z boson resonant region. The data (black markers with error bars representing statistical uncertainties) are overlaid on top of the stacked contributions from the expected $ \mathrm{t} \overline{\mathrm{t}} $ (blue), nonprompt (light orange), WW (red), single top quark (gray), and $ \mathrm{DY} $ (violet) processes. The last bin includes the overflow entries. In the left panel, the event counts are divided by the variable bin width. |
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Figure 1-b:
Distributions of dilepton $ p_{\mathrm{T}}(\ell\ell) $ (left) and invariant mass $ m(\ell\ell) $ (right) variables in the same-flavor ($ \ell\ell $) channels. The $ m(\ell\ell) $ distribution is shown before applying the veto of the Z boson resonant region. The data (black markers with error bars representing statistical uncertainties) are overlaid on top of the stacked contributions from the expected $ \mathrm{t} \overline{\mathrm{t}} $ (blue), nonprompt (light orange), WW (red), single top quark (gray), and $ \mathrm{DY} $ (violet) processes. The last bin includes the overflow entries. In the left panel, the event counts are divided by the variable bin width. |
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Figure 2:
Distributions of $ p_{\mathrm{T}}(\ell_2) $ (upper left), $ p_{\mathrm{T}}(\ell\ell) $ (upper right), and $ \sum|\eta_\ell| $ (lower) variables in the different-flavor ($ \mathrm{e}^{\mp}\mu^{\pm} $) channel. The data (black markers with error bars representing statistical uncertainties) are overlaid on top of the stacked contributions from the expected $ \mathrm{t} \overline{\mathrm{t}} $ (blue), nonprompt (light orange), WW (red), single top quark (gray), and $ \mathrm{DY} $ (violet) processes. The last bin includes the overflow entries. |
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Figure 2-a:
Distributions of $ p_{\mathrm{T}}(\ell_2) $ (upper left), $ p_{\mathrm{T}}(\ell\ell) $ (upper right), and $ \sum|\eta_\ell| $ (lower) variables in the different-flavor ($ \mathrm{e}^{\mp}\mu^{\pm} $) channel. The data (black markers with error bars representing statistical uncertainties) are overlaid on top of the stacked contributions from the expected $ \mathrm{t} \overline{\mathrm{t}} $ (blue), nonprompt (light orange), WW (red), single top quark (gray), and $ \mathrm{DY} $ (violet) processes. The last bin includes the overflow entries. |
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Figure 2-b:
Distributions of $ p_{\mathrm{T}}(\ell_2) $ (upper left), $ p_{\mathrm{T}}(\ell\ell) $ (upper right), and $ \sum|\eta_\ell| $ (lower) variables in the different-flavor ($ \mathrm{e}^{\mp}\mu^{\pm} $) channel. The data (black markers with error bars representing statistical uncertainties) are overlaid on top of the stacked contributions from the expected $ \mathrm{t} \overline{\mathrm{t}} $ (blue), nonprompt (light orange), WW (red), single top quark (gray), and $ \mathrm{DY} $ (violet) processes. The last bin includes the overflow entries. |
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Figure 2-c:
Distributions of $ p_{\mathrm{T}}(\ell_2) $ (upper left), $ p_{\mathrm{T}}(\ell\ell) $ (upper right), and $ \sum|\eta_\ell| $ (lower) variables in the different-flavor ($ \mathrm{e}^{\mp}\mu^{\pm} $) channel. The data (black markers with error bars representing statistical uncertainties) are overlaid on top of the stacked contributions from the expected $ \mathrm{t} \overline{\mathrm{t}} $ (blue), nonprompt (light orange), WW (red), single top quark (gray), and $ \mathrm{DY} $ (violet) processes. The last bin includes the overflow entries. |
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Figure 3:
Distribution of the $ x_\mathrm{j}=p_{\mathrm{T}} $ (jet) $ /p_{\mathrm{T}}(\mathrm{Z}) $ ratio in $ \mathrm{Z}+\text{jet} $ events in the 0--10% (left) and 10--90% (right) $ \mathrm{Pb}\mathrm{Pb} $ centralities. The data (solid dots with error bars) are compared with the contributions from UE jets (gray histograms) and true recoil jets (black dashed curves) stacked. The blue curves show the sum of UE and recoil jet contributions. |
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Figure 3-a:
Distribution of the $ x_\mathrm{j}=p_{\mathrm{T}} $ (jet) $ /p_{\mathrm{T}}(\mathrm{Z}) $ ratio in $ \mathrm{Z}+\text{jet} $ events in the 0--10% (left) and 10--90% (right) $ \mathrm{Pb}\mathrm{Pb} $ centralities. The data (solid dots with error bars) are compared with the contributions from UE jets (gray histograms) and true recoil jets (black dashed curves) stacked. The blue curves show the sum of UE and recoil jet contributions. |
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Figure 3-b:
Distribution of the $ x_\mathrm{j}=p_{\mathrm{T}} $ (jet) $ /p_{\mathrm{T}}(\mathrm{Z}) $ ratio in $ \mathrm{Z}+\text{jet} $ events in the 0--10% (left) and 10--90% (right) $ \mathrm{Pb}\mathrm{Pb} $ centralities. The data (solid dots with error bars) are compared with the contributions from UE jets (gray histograms) and true recoil jets (black dashed curves) stacked. The blue curves show the sum of UE and recoil jet contributions. |
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Figure 4:
Ratio of the average $ \langle{x_\mathrm{j}}\rangle $ detector-level distributions measured in data over simulation as a function of the collision centrality with a fit to an error function (blue dashed curve) superimposed. |
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Figure 5:
Multiplicities of inclusive (upper) and b-tagged (lower) jets in Z boson candidate events in the 0--10% (left) and 10--90% (right) centrality bins measured in the data (black markers) compared with the post-fit stacked model of the $ \mathrm{t} \overline{\mathrm{t}} $ (blue), nonprompt (light orange), WW (red), single top quark (gray), and $ \mathrm{DY} $ (violet) contributions. The lower panels show the data-to-expectation ratios before (orange lines) and after (black markers) the fit. The hatched band represents the post-fit uncertainty of the model in each bin. The last bins include the overflow entries. |
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Figure 5-a:
Multiplicities of inclusive (upper) and b-tagged (lower) jets in Z boson candidate events in the 0--10% (left) and 10--90% (right) centrality bins measured in the data (black markers) compared with the post-fit stacked model of the $ \mathrm{t} \overline{\mathrm{t}} $ (blue), nonprompt (light orange), WW (red), single top quark (gray), and $ \mathrm{DY} $ (violet) contributions. The lower panels show the data-to-expectation ratios before (orange lines) and after (black markers) the fit. The hatched band represents the post-fit uncertainty of the model in each bin. The last bins include the overflow entries. |
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Figure 5-b:
Multiplicities of inclusive (upper) and b-tagged (lower) jets in Z boson candidate events in the 0--10% (left) and 10--90% (right) centrality bins measured in the data (black markers) compared with the post-fit stacked model of the $ \mathrm{t} \overline{\mathrm{t}} $ (blue), nonprompt (light orange), WW (red), single top quark (gray), and $ \mathrm{DY} $ (violet) contributions. The lower panels show the data-to-expectation ratios before (orange lines) and after (black markers) the fit. The hatched band represents the post-fit uncertainty of the model in each bin. The last bins include the overflow entries. |
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Figure 5-c:
Multiplicities of inclusive (upper) and b-tagged (lower) jets in Z boson candidate events in the 0--10% (left) and 10--90% (right) centrality bins measured in the data (black markers) compared with the post-fit stacked model of the $ \mathrm{t} \overline{\mathrm{t}} $ (blue), nonprompt (light orange), WW (red), single top quark (gray), and $ \mathrm{DY} $ (violet) contributions. The lower panels show the data-to-expectation ratios before (orange lines) and after (black markers) the fit. The hatched band represents the post-fit uncertainty of the model in each bin. The last bins include the overflow entries. |
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Figure 5-d:
Multiplicities of inclusive (upper) and b-tagged (lower) jets in Z boson candidate events in the 0--10% (left) and 10--90% (right) centrality bins measured in the data (black markers) compared with the post-fit stacked model of the $ \mathrm{t} \overline{\mathrm{t}} $ (blue), nonprompt (light orange), WW (red), single top quark (gray), and $ \mathrm{DY} $ (violet) contributions. The lower panels show the data-to-expectation ratios before (orange lines) and after (black markers) the fit. The hatched band represents the post-fit uncertainty of the model in each bin. The last bins include the overflow entries. |
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Figure 6:
Distributions of the final BDT discriminator after the fit for the same-flavor $ \ell\ell $ (upper) and different-flavor $ \mathrm{e}^{\mp}\mu^{\pm} $ (lower) channels. The discriminator output is shown for 0, 1, and $ \geq $ 2 b-tagged jet events. The left (right) figures correspond to events reconstructed in the 0--10% (10--90%) centrality bin. The data (black markers) are compared with the stacked histograms corresponding to the $ \mathrm{t} \overline{\mathrm{t}} $ signal (blue), and the nonprompt (light orange), WW (red), single top quark (gray), and $ \mathrm{DY} $ (violet) background processes normalized to their post-fit expectations. The hatched gray bands show the total uncertainty in the predicted yields after the fit is performed. |
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Figure 6-a:
Distributions of the final BDT discriminator after the fit for the same-flavor $ \ell\ell $ (upper) and different-flavor $ \mathrm{e}^{\mp}\mu^{\pm} $ (lower) channels. The discriminator output is shown for 0, 1, and $ \geq $ 2 b-tagged jet events. The left (right) figures correspond to events reconstructed in the 0--10% (10--90%) centrality bin. The data (black markers) are compared with the stacked histograms corresponding to the $ \mathrm{t} \overline{\mathrm{t}} $ signal (blue), and the nonprompt (light orange), WW (red), single top quark (gray), and $ \mathrm{DY} $ (violet) background processes normalized to their post-fit expectations. The hatched gray bands show the total uncertainty in the predicted yields after the fit is performed. |
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Figure 6-b:
Distributions of the final BDT discriminator after the fit for the same-flavor $ \ell\ell $ (upper) and different-flavor $ \mathrm{e}^{\mp}\mu^{\pm} $ (lower) channels. The discriminator output is shown for 0, 1, and $ \geq $ 2 b-tagged jet events. The left (right) figures correspond to events reconstructed in the 0--10% (10--90%) centrality bin. The data (black markers) are compared with the stacked histograms corresponding to the $ \mathrm{t} \overline{\mathrm{t}} $ signal (blue), and the nonprompt (light orange), WW (red), single top quark (gray), and $ \mathrm{DY} $ (violet) background processes normalized to their post-fit expectations. The hatched gray bands show the total uncertainty in the predicted yields after the fit is performed. |
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Figure 6-c:
Distributions of the final BDT discriminator after the fit for the same-flavor $ \ell\ell $ (upper) and different-flavor $ \mathrm{e}^{\mp}\mu^{\pm} $ (lower) channels. The discriminator output is shown for 0, 1, and $ \geq $ 2 b-tagged jet events. The left (right) figures correspond to events reconstructed in the 0--10% (10--90%) centrality bin. The data (black markers) are compared with the stacked histograms corresponding to the $ \mathrm{t} \overline{\mathrm{t}} $ signal (blue), and the nonprompt (light orange), WW (red), single top quark (gray), and $ \mathrm{DY} $ (violet) background processes normalized to their post-fit expectations. The hatched gray bands show the total uncertainty in the predicted yields after the fit is performed. |
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Figure 6-d:
Distributions of the final BDT discriminator after the fit for the same-flavor $ \ell\ell $ (upper) and different-flavor $ \mathrm{e}^{\mp}\mu^{\pm} $ (lower) channels. The discriminator output is shown for 0, 1, and $ \geq $ 2 b-tagged jet events. The left (right) figures correspond to events reconstructed in the 0--10% (10--90%) centrality bin. The data (black markers) are compared with the stacked histograms corresponding to the $ \mathrm{t} \overline{\mathrm{t}} $ signal (blue), and the nonprompt (light orange), WW (red), single top quark (gray), and $ \mathrm{DY} $ (violet) background processes normalized to their post-fit expectations. The hatched gray bands show the total uncertainty in the predicted yields after the fit is performed. |
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Figure 7:
Scan of the profile likelihood as a function of the $ \mathrm{t} \overline{\mathrm{t}} $ signal strength. The expected (orange) and observed (black) scans are displayed with (solid curve) and without (dashed curve) accounting for systematic uncertainties. The horizontal dashed lines indicate the likelihood values used to extract the 68% and 95% CL intervals on the parameter of interest. |
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Figure 8:
Impact of systematic uncertainties on the fitted $ \mathrm{t} \overline{\mathrm{t}} $ signal strength parameter. The systematic uncertainties are listed in decreasing order of their impact on the signal strength. |
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Figure 9:
Experimental measurements (colored bands) of the $ \mathrm{t} \overline{\mathrm{t}} $ cross section (upper), DY cross section (middle), and $ R_{{\mathrm{t}\overline{\mathrm{t}}} /\mathrm{DY}} $ ratio (lower) in inclusive $ \mathrm{Pb}\mathrm{Pb} $ collisions at $ \sqrt{\smash[b]{s_{_{\mathrm{NN}}}}}= $ 5.36 TeV compared with the corresponding NLO (red bars) or NNLO $ + $ NNLL (black bars) theoretical predictions obtained with the EPPS21_nlo, nNNPDF10_(n)nlo, nNNPDF30_nlo, and TUJU21_(n)nlo nPDF sets. The error bars represent the theoretical uncertainties, and the blue (orange) area shows the total (statistical) uncertainties of the measurements. In the upper plot a dashed line separates the theory predictions obtained with nuclear PDFs (above the line) from those with the proton PDFs (below the line). |
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Figure 9-a:
Experimental measurements (colored bands) of the $ \mathrm{t} \overline{\mathrm{t}} $ cross section (upper), DY cross section (middle), and $ R_{{\mathrm{t}\overline{\mathrm{t}}} /\mathrm{DY}} $ ratio (lower) in inclusive $ \mathrm{Pb}\mathrm{Pb} $ collisions at $ \sqrt{\smash[b]{s_{_{\mathrm{NN}}}}}= $ 5.36 TeV compared with the corresponding NLO (red bars) or NNLO $ + $ NNLL (black bars) theoretical predictions obtained with the EPPS21_nlo, nNNPDF10_(n)nlo, nNNPDF30_nlo, and TUJU21_(n)nlo nPDF sets. The error bars represent the theoretical uncertainties, and the blue (orange) area shows the total (statistical) uncertainties of the measurements. In the upper plot a dashed line separates the theory predictions obtained with nuclear PDFs (above the line) from those with the proton PDFs (below the line). |
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Figure 9-b:
Experimental measurements (colored bands) of the $ \mathrm{t} \overline{\mathrm{t}} $ cross section (upper), DY cross section (middle), and $ R_{{\mathrm{t}\overline{\mathrm{t}}} /\mathrm{DY}} $ ratio (lower) in inclusive $ \mathrm{Pb}\mathrm{Pb} $ collisions at $ \sqrt{\smash[b]{s_{_{\mathrm{NN}}}}}= $ 5.36 TeV compared with the corresponding NLO (red bars) or NNLO $ + $ NNLL (black bars) theoretical predictions obtained with the EPPS21_nlo, nNNPDF10_(n)nlo, nNNPDF30_nlo, and TUJU21_(n)nlo nPDF sets. The error bars represent the theoretical uncertainties, and the blue (orange) area shows the total (statistical) uncertainties of the measurements. In the upper plot a dashed line separates the theory predictions obtained with nuclear PDFs (above the line) from those with the proton PDFs (below the line). |
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Figure 9-c:
Experimental measurements (colored bands) of the $ \mathrm{t} \overline{\mathrm{t}} $ cross section (upper), DY cross section (middle), and $ R_{{\mathrm{t}\overline{\mathrm{t}}} /\mathrm{DY}} $ ratio (lower) in inclusive $ \mathrm{Pb}\mathrm{Pb} $ collisions at $ \sqrt{\smash[b]{s_{_{\mathrm{NN}}}}}= $ 5.36 TeV compared with the corresponding NLO (red bars) or NNLO $ + $ NNLL (black bars) theoretical predictions obtained with the EPPS21_nlo, nNNPDF10_(n)nlo, nNNPDF30_nlo, and TUJU21_(n)nlo nPDF sets. The error bars represent the theoretical uncertainties, and the blue (orange) area shows the total (statistical) uncertainties of the measurements. In the upper plot a dashed line separates the theory predictions obtained with nuclear PDFs (above the line) from those with the proton PDFs (below the line). |
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Figure 10:
Experimental measurements (colored bands) of the $ \mathrm{t} \overline{\mathrm{t}} $ cross section (upper), DY cross section (middle), and $ R_{{\mathrm{t}\overline{\mathrm{t}}} /\mathrm{DY}} $ ratio (lower) in semicentral (10--90%), central (0--10%), and inclusive $ \mathrm{Pb}\mathrm{Pb} $ collisions at $ \sqrt{\smash[b]{s_{_{\mathrm{NN}}}}}= $ 5.36 TeV compared with the corresponding NNLO $ + $ NNLL theoretical predictions (black markers with error bars) obtained with the EPPS21_nlo [23] nPDF set. The blue (orange) bands indicate the total (statistical) uncertainties of the measured observables, whereas the error bars represent the uncertainties in the theory calculations. |
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Figure 10-a:
Experimental measurements (colored bands) of the $ \mathrm{t} \overline{\mathrm{t}} $ cross section (upper), DY cross section (middle), and $ R_{{\mathrm{t}\overline{\mathrm{t}}} /\mathrm{DY}} $ ratio (lower) in semicentral (10--90%), central (0--10%), and inclusive $ \mathrm{Pb}\mathrm{Pb} $ collisions at $ \sqrt{\smash[b]{s_{_{\mathrm{NN}}}}}= $ 5.36 TeV compared with the corresponding NNLO $ + $ NNLL theoretical predictions (black markers with error bars) obtained with the EPPS21_nlo [23] nPDF set. The blue (orange) bands indicate the total (statistical) uncertainties of the measured observables, whereas the error bars represent the uncertainties in the theory calculations. |
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Figure 10-b:
Experimental measurements (colored bands) of the $ \mathrm{t} \overline{\mathrm{t}} $ cross section (upper), DY cross section (middle), and $ R_{{\mathrm{t}\overline{\mathrm{t}}} /\mathrm{DY}} $ ratio (lower) in semicentral (10--90%), central (0--10%), and inclusive $ \mathrm{Pb}\mathrm{Pb} $ collisions at $ \sqrt{\smash[b]{s_{_{\mathrm{NN}}}}}= $ 5.36 TeV compared with the corresponding NNLO $ + $ NNLL theoretical predictions (black markers with error bars) obtained with the EPPS21_nlo [23] nPDF set. The blue (orange) bands indicate the total (statistical) uncertainties of the measured observables, whereas the error bars represent the uncertainties in the theory calculations. |
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Figure 10-c:
Experimental measurements (colored bands) of the $ \mathrm{t} \overline{\mathrm{t}} $ cross section (upper), DY cross section (middle), and $ R_{{\mathrm{t}\overline{\mathrm{t}}} /\mathrm{DY}} $ ratio (lower) in semicentral (10--90%), central (0--10%), and inclusive $ \mathrm{Pb}\mathrm{Pb} $ collisions at $ \sqrt{\smash[b]{s_{_{\mathrm{NN}}}}}= $ 5.36 TeV compared with the corresponding NNLO $ + $ NNLL theoretical predictions (black markers with error bars) obtained with the EPPS21_nlo [23] nPDF set. The blue (orange) bands indicate the total (statistical) uncertainties of the measured observables, whereas the error bars represent the uncertainties in the theory calculations. |
| Tables | |
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Table 1:
Measured $ \mathrm{t} \overline{\mathrm{t}} $ cross section, DY cross section, and $ R_{{\mathrm{t}\overline{\mathrm{t}}} /\mathrm{DY}} $ ratio for three different $ \mathrm{Pb}\mathrm{Pb} $ centrality selections. For each measurement, the statistical and systematic uncertainty components are shown separately. |
| Summary |
| The first measurement of the inclusive production of top quark pairs ($ {\mathrm{t}\overline{\mathrm{t}}} $) in lead-lead ($ \mathrm{Pb}\mathrm{Pb} $) collisions at a nucleon-nucleon center-of-mass energy of $ \sqrt{\smash[b]{s_{_{\mathrm{NN}}}}}= $ 5.36 TeV has been presented, extending earlier studies performed at lower collision energies. The analysis is based on dilepton events selected from the 2023 dataset recorded by the CMS experiment, corresponding to an integrated luminosity of 1.58$ \text{nb}^{-1}$. Several improvements have been implemented---including enhanced electron identification and lepton isolation, refined heavy-flavor jet identification, and a dedicated calibration of the b jet energy scale---which collectively provide a substantial gain in precision compared with previous analyses. The cross sections $ \sigma_{{\mathrm{t}\overline{\mathrm{t}}} }= $ 3.42 $ ^{+0.54}_{-0.51} $ $ $ (stat) $ ^{+0.50}_{-0.43} $ (syst) $\mu b$, and $ \sigma_\text{DY}= $ 397 $ \pm $ 3 (stat) $ ^{+27}_{-25} $ (syst) $\mu b$ for the Drell--Yan process, along with their ratio $ R_{{\mathrm{t}\overline{\mathrm{t}}} /\mathrm{DY}}= $ 0.0086 $ ^{+0.0014}_{-0.0013} $ $ $ (stat) $ ^{+0.0011}_{-0.0010} $ (syst), have been measured. The $ \sigma_{{\mathrm{t}\overline{\mathrm{t}}} } $ and $ R_{{\mathrm{t}\overline{\mathrm{t}}} /\mathrm{DY}} $ measurements have total uncertainties of $ {\approx}20% $ and are consistent with perturbative quantum chromodynamics calculations at next-to-next-to-leading-order accuracy obtained using different nuclear parton distribution functions. Results for central and semicentral $ \mathrm{Pb}\mathrm{Pb} $ collisions are also reported for the first time to examine the dependence of the top quark yields on the collision impact parameter. Combined with the higher collision energy and the larger data samples anticipated for the remainder of Run 3, these developments firmly establish top quark production as a future probe of initial- and final-state effects in heavy ions. |
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