CMS-PAS-TOP-12-028

CMS-PAS-TOP-12-028
Measurement of the differential top-quark pair production cross section in the dilepton channel in pp collisions at $\sqrt{s} =$ 8 TeV
CMS Collaboration
2013

Abstract: Normalised differential top-quark pair production cross sections are measured in pp collisions at a centre-of-mass energy of 8 TeV at the LHC with the CMS detector using data recorded in 2012 corresponding to an integrated luminosity of 12.2 fb $^{-1}.$ The measurements are performed in the dilepton decay channels ( $\mathrm{e^+e^-}$ , $\mu^+\mu^-$ , and $\mu^{\pm} \mathrm{e^{\mp}}$ ). The $\mathrm{t \bar t}$ production cross section is measured as a function of kinematic properties of the final-state charged leptons and jets associated to b quarks, as well as those of the top quarks and the $\mathrm{t \bar t}$ system. The data are compared with several predictions from perturbative QCD calculations up to approximate next-to-next-to-leading-order precision. No significant deviations from the standard model are observed.
Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ; These preliminary results are superseded in this paper, EPJC 75 (2015) 542. The superseded preliminary plots can be found here.

Figures	Summary	References	CMS Publications

Figures
png pdf	Figure 1-a: Kinematic distributions after event selection for the dilepton channels. The (a) plot shows the multiplicity of the reconstructed b-tagged jets. The multiplicity of the reconstructed jets (b), the ${p_{\mathrm {T}}}$ of the highest ${p_{\mathrm {T}}}$ (leading) isolated leptons (c), and the ${p_{\mathrm {T}}}$ of the leading b jet (d) are shown after the b-tagging requirement. The normalisation of the Z/ $\gamma ^{*}$ +jets background is determined from data.
png pdf	Figure 1-b: Kinematic distributions after event selection for the dilepton channels. The (a) plot shows the multiplicity of the reconstructed b-tagged jets. The multiplicity of the reconstructed jets (b), the ${p_{\mathrm {T}}}$ of the highest ${p_{\mathrm {T}}}$ (leading) isolated leptons (c), and the ${p_{\mathrm {T}}}$ of the leading b jet (d) are shown after the b-tagging requirement. The normalisation of the Z/ $\gamma ^{*}$ +jets background is determined from data.
png pdf	Figure 1-c: Kinematic distributions after event selection for the dilepton channels. The (a) plot shows the multiplicity of the reconstructed b-tagged jets. The multiplicity of the reconstructed jets (b), the ${p_{\mathrm {T}}}$ of the highest ${p_{\mathrm {T}}}$ (leading) isolated leptons (c), and the ${p_{\mathrm {T}}}$ of the leading b jet (d) are shown after the b-tagging requirement. The normalisation of the Z/ $\gamma ^{*}$ +jets background is determined from data.
png pdf	Figure 1-d: Kinematic distributions after event selection for the dilepton channels. The (a) plot shows the multiplicity of the reconstructed b-tagged jets. The multiplicity of the reconstructed jets (b), the ${p_{\mathrm {T}}}$ of the highest ${p_{\mathrm {T}}}$ (leading) isolated leptons (c), and the ${p_{\mathrm {T}}}$ of the leading b jet (d) are shown after the b-tagging requirement. The normalisation of the Z/ $\gamma ^{*}$ +jets background is determined from data.
png pdf	Figure 2-a: Distribution of the leading top quark (a) and of ${\mathrm{ t \bar{t} } }$ quantities (b) as obtained from the kinematic reconstruction. The (a,b) plots show the transverse momenta, and the (c,s) plots show the rapidities. The normalisation of the Z/ $\gamma ^{*}$ +jets background is determined from data.
png pdf	Figure 2-b: Distribution of the leading top quark (a) and of ${\mathrm{ t \bar{t} } }$ quantities (b) as obtained from the kinematic reconstruction. The (a,b) plots show the transverse momenta, and the (c,s) plots show the rapidities. The normalisation of the Z/ $\gamma ^{*}$ +jets background is determined from data.
png pdf	Figure 2-c: Distribution of the leading top quark (a) and of ${\mathrm{ t \bar{t} } }$ quantities (b) as obtained from the kinematic reconstruction. The (a,b) plots show the transverse momenta, and the (c,s) plots show the rapidities. The normalisation of the Z/ $\gamma ^{*}$ +jets background is determined from data.
png pdf	Figure 2-d: Distribution of the leading top quark (a) and of ${\mathrm{ t \bar{t} } }$ quantities (b) as obtained from the kinematic reconstruction. The (a,b) plots show the transverse momenta, and the (c,s) plots show the rapidities. The normalisation of the Z/ $\gamma ^{*}$ +jets background is determined from data.
png pdf	Figure 3-a: Normalised differential ${\mathrm{ t \bar{t} } }$ production cross section as a function of the ${p_{\mathrm {T}}} ^{\ell }$ (a,b) and $\eta ^{\ell }$ (c,d) of the leading and next-to-leading lepton, and the ${p_{\mathrm {T}}} ^{\ell ^{+}\ell ^{-}}$ (e), and $m^{\ell ^{+}\ell ^{-}}$ (f) of the lepton pair. The superscript ` $\ell$ ' refers to both $\ell ^{+}$ and $\ell ^{-}$ . The inner (outer) error bars indicate the statistical (combined statistical and systematic) uncertainty. The measurements are compared to predictions from MadGraph +PYTHIA , POWHEG +PYTHIA , and MC@NLO+HERWIG. The MadGraph +PYTHIA prediction is shown both as a curve and as a binned histogram.
png pdf	Figure 3-b: Normalised differential ${\mathrm{ t \bar{t} } }$ production cross section as a function of the ${p_{\mathrm {T}}} ^{\ell }$ (a,b) and $\eta ^{\ell }$ (c,d) of the leading and next-to-leading lepton, and the ${p_{\mathrm {T}}} ^{\ell ^{+}\ell ^{-}}$ (e), and $m^{\ell ^{+}\ell ^{-}}$ (f) of the lepton pair. The superscript ` $\ell$ ' refers to both $\ell ^{+}$ and $\ell ^{-}$ . The inner (outer) error bars indicate the statistical (combined statistical and systematic) uncertainty. The measurements are compared to predictions from MadGraph +PYTHIA , POWHEG +PYTHIA , and MC@NLO+HERWIG. The MadGraph +PYTHIA prediction is shown both as a curve and as a binned histogram.
png pdf	Figure 3-c: Normalised differential ${\mathrm{ t \bar{t} } }$ production cross section as a function of the ${p_{\mathrm {T}}} ^{\ell }$ (a,b) and $\eta ^{\ell }$ (c,d) of the leading and next-to-leading lepton, and the ${p_{\mathrm {T}}} ^{\ell ^{+}\ell ^{-}}$ (e), and $m^{\ell ^{+}\ell ^{-}}$ (f) of the lepton pair. The superscript ` $\ell$ ' refers to both $\ell ^{+}$ and $\ell ^{-}$ . The inner (outer) error bars indicate the statistical (combined statistical and systematic) uncertainty. The measurements are compared to predictions from MadGraph +PYTHIA , POWHEG +PYTHIA , and MC@NLO+HERWIG. The MadGraph +PYTHIA prediction is shown both as a curve and as a binned histogram.
png pdf	Figure 3-d: Normalised differential ${\mathrm{ t \bar{t} } }$ production cross section as a function of the ${p_{\mathrm {T}}} ^{\ell }$ (a,b) and $\eta ^{\ell }$ (c,d) of the leading and next-to-leading lepton, and the ${p_{\mathrm {T}}} ^{\ell ^{+}\ell ^{-}}$ (e), and $m^{\ell ^{+}\ell ^{-}}$ (f) of the lepton pair. The superscript ` $\ell$ ' refers to both $\ell ^{+}$ and $\ell ^{-}$ . The inner (outer) error bars indicate the statistical (combined statistical and systematic) uncertainty. The measurements are compared to predictions from MadGraph +PYTHIA , POWHEG +PYTHIA , and MC@NLO+HERWIG. The MadGraph +PYTHIA prediction is shown both as a curve and as a binned histogram.
png pdf	Figure 3-e: Normalised differential ${\mathrm{ t \bar{t} } }$ production cross section as a function of the ${p_{\mathrm {T}}} ^{\ell }$ (a,b) and $\eta ^{\ell }$ (c,d) of the leading and next-to-leading lepton, and the ${p_{\mathrm {T}}} ^{\ell ^{+}\ell ^{-}}$ (e), and $m^{\ell ^{+}\ell ^{-}}$ (f) of the lepton pair. The superscript ` $\ell$ ' refers to both $\ell ^{+}$ and $\ell ^{-}$ . The inner (outer) error bars indicate the statistical (combined statistical and systematic) uncertainty. The measurements are compared to predictions from MadGraph +PYTHIA , POWHEG +PYTHIA , and MC@NLO+HERWIG. The MadGraph +PYTHIA prediction is shown both as a curve and as a binned histogram.
png pdf	Figure 3-f: Normalised differential ${\mathrm{ t \bar{t} } }$ production cross section as a function of the ${p_{\mathrm {T}}} ^{\ell }$ (a,b) and $\eta ^{\ell }$ (c,d) of the leading and next-to-leading lepton, and the ${p_{\mathrm {T}}} ^{\ell ^{+}\ell ^{-}}$ (e), and $m^{\ell ^{+}\ell ^{-}}$ (f) of the lepton pair. The superscript ` $\ell$ ' refers to both $\ell ^{+}$ and $\ell ^{-}$ . The inner (outer) error bars indicate the statistical (combined statistical and systematic) uncertainty. The measurements are compared to predictions from MadGraph +PYTHIA , POWHEG +PYTHIA , and MC@NLO+HERWIG. The MadGraph +PYTHIA prediction is shown both as a curve and as a binned histogram.
png pdf	Figure 4-a: Normalised differential ${\mathrm{ t \bar{t} } }$ production cross section as a function of the ${p_{\mathrm {T}}} ^{\text {b}}$ (a,b) and $\eta ^{\text {b}}$ of the leading and next-to-leading b jet (c,d), and the invariant mass of the lepton and b jet $m^{\ell \rm {b}}$ (e). The superscript `b' refers to both b and b-bar jets. The inner (outer) error bars indicate the statistical (combined statistical and systematic) uncertainty. The measurements are compared to predictions from MadGraph +PYTHIA , POWHEG +PYTHIA , and MC@NLO+HERWIG. The MadGraph +PYTHIA prediction is shown both as a curve and as a binned histogram when available.
png pdf	Figure 4-b: Normalised differential ${\mathrm{ t \bar{t} } }$ production cross section as a function of the ${p_{\mathrm {T}}} ^{\text {b}}$ (a,b) and $\eta ^{\text {b}}$ of the leading and next-to-leading b jet (c,d), and the invariant mass of the lepton and b jet $m^{\ell \rm {b}}$ (e). The superscript `b' refers to both b and b-bar jets. The inner (outer) error bars indicate the statistical (combined statistical and systematic) uncertainty. The measurements are compared to predictions from MadGraph +PYTHIA , POWHEG +PYTHIA , and MC@NLO+HERWIG. The MadGraph +PYTHIA prediction is shown both as a curve and as a binned histogram when available.
png pdf	Figure 4-c: Normalised differential ${\mathrm{ t \bar{t} } }$ production cross section as a function of the ${p_{\mathrm {T}}} ^{\text {b}}$ (a,b) and $\eta ^{\text {b}}$ of the leading and next-to-leading b jet (c,d), and the invariant mass of the lepton and b jet $m^{\ell \rm {b}}$ (e). The superscript `b' refers to both b and b-bar jets. The inner (outer) error bars indicate the statistical (combined statistical and systematic) uncertainty. The measurements are compared to predictions from MadGraph +PYTHIA , POWHEG +PYTHIA , and MC@NLO+HERWIG. The MadGraph +PYTHIA prediction is shown both as a curve and as a binned histogram when available.
png pdf	Figure 4-d: Normalised differential ${\mathrm{ t \bar{t} } }$ production cross section as a function of the ${p_{\mathrm {T}}} ^{\text {b}}$ (a,b) and $\eta ^{\text {b}}$ of the leading and next-to-leading b jet (c,d), and the invariant mass of the lepton and b jet $m^{\ell \rm {b}}$ (e). The superscript `b' refers to both b and b-bar jets. The inner (outer) error bars indicate the statistical (combined statistical and systematic) uncertainty. The measurements are compared to predictions from MadGraph +PYTHIA , POWHEG +PYTHIA , and MC@NLO+HERWIG. The MadGraph +PYTHIA prediction is shown both as a curve and as a binned histogram when available.
png pdf	Figure 4-e: Normalised differential ${\mathrm{ t \bar{t} } }$ production cross section as a function of the ${p_{\mathrm {T}}} ^{\text {b}}$ (a,b) and $\eta ^{\text {b}}$ of the leading and next-to-leading b jet (c,d), and the invariant mass of the lepton and b jet $m^{\ell \rm {b}}$ (e). The superscript `b' refers to both b and b-bar jets. The inner (outer) error bars indicate the statistical (combined statistical and systematic) uncertainty. The measurements are compared to predictions from MadGraph +PYTHIA , POWHEG +PYTHIA , and MC@NLO+HERWIG. The MadGraph +PYTHIA prediction is shown both as a curve and as a binned histogram when available.
png pdf	Figure 5-a: Normalised differential ${\mathrm{ t \bar{t} } }$ production cross section as a function of the ${p_{\mathrm {T}}} ^{\text {t}}$ (a,b) and $y^{\text {t}}$ (c,d) of the leading and next-to-leading top quarks or antiquarks. The inner (outer) error bars indicate the statistical (combined statistical and systematic) uncertainty. The measurements are compared to predictions from MadGraph +PYTHIA , POWHEG +PYTHIA , and MC@NLO+HERWIG. The MadGraph +PYTHIA prediction is shown both as a curve and as a binned histogram.
png pdf	Figure 5-b: Normalised differential ${\mathrm{ t \bar{t} } }$ production cross section as a function of the ${p_{\mathrm {T}}} ^{\text {t}}$ (a,b) and $y^{\text {t}}$ (c,d) of the leading and next-to-leading top quarks or antiquarks. The inner (outer) error bars indicate the statistical (combined statistical and systematic) uncertainty. The measurements are compared to predictions from MadGraph +PYTHIA , POWHEG +PYTHIA , and MC@NLO+HERWIG. The MadGraph +PYTHIA prediction is shown both as a curve and as a binned histogram.
png pdf	Figure 5-c: Normalised differential ${\mathrm{ t \bar{t} } }$ production cross section as a function of the ${p_{\mathrm {T}}} ^{\text {t}}$ (a,b) and $y^{\text {t}}$ (c,d) of the leading and next-to-leading top quarks or antiquarks. The inner (outer) error bars indicate the statistical (combined statistical and systematic) uncertainty. The measurements are compared to predictions from MadGraph +PYTHIA , POWHEG +PYTHIA , and MC@NLO+HERWIG. The MadGraph +PYTHIA prediction is shown both as a curve and as a binned histogram.
png pdf	Figure 5-d: Normalised differential ${\mathrm{ t \bar{t} } }$ production cross section as a function of the ${p_{\mathrm {T}}} ^{\text {t}}$ (a,b) and $y^{\text {t}}$ (c,d) of the leading and next-to-leading top quarks or antiquarks. The inner (outer) error bars indicate the statistical (combined statistical and systematic) uncertainty. The measurements are compared to predictions from MadGraph +PYTHIA , POWHEG +PYTHIA , and MC@NLO+HERWIG. The MadGraph +PYTHIA prediction is shown both as a curve and as a binned histogram.
png pdf	Figure 6-a: Normalised differential ${\mathrm{ t \bar{t} } }$ production cross section as a function of the ${p_{\mathrm {T}}} ^{\text {t}}$ (a) and $y^{\text {t}}$ (b) of the top quarks or antiquarks, the ${p_{\mathrm {T}}} ^{ {\mathrm{ t \bar{t} } } }$ (c), $m^{ {\mathrm{ t \bar{t} } } }$ (d), and $y^{ {\mathrm{ t \bar{t} } } }$ (e) of the top-quark pairs. The inner (outer) error bars indicate the statistical (combined statistical and systematic) uncertainty. The measurements are compared to predictions from MadGraph +PYTHIA , POWHEG +PYTHIA , MC@NLO+HERWIG, and to an approximate NNLO calculation [8], when available. The MadGraph +PYTHIA prediction is shown both as a curve and as a binned histogram.
png pdf	Figure 6-b: Normalised differential ${\mathrm{ t \bar{t} } }$ production cross section as a function of the ${p_{\mathrm {T}}} ^{\text {t}}$ (a) and $y^{\text {t}}$ (b) of the top quarks or antiquarks, the ${p_{\mathrm {T}}} ^{ {\mathrm{ t \bar{t} } } }$ (c), $m^{ {\mathrm{ t \bar{t} } } }$ (d), and $y^{ {\mathrm{ t \bar{t} } } }$ (e) of the top-quark pairs. The inner (outer) error bars indicate the statistical (combined statistical and systematic) uncertainty. The measurements are compared to predictions from MadGraph +PYTHIA , POWHEG +PYTHIA , MC@NLO+HERWIG, and to an approximate NNLO calculation [8], when available. The MadGraph +PYTHIA prediction is shown both as a curve and as a binned histogram.
png pdf	Figure 6-c: Normalised differential ${\mathrm{ t \bar{t} } }$ production cross section as a function of the ${p_{\mathrm {T}}} ^{\text {t}}$ (a) and $y^{\text {t}}$ (b) of the top quarks or antiquarks, the ${p_{\mathrm {T}}} ^{ {\mathrm{ t \bar{t} } } }$ (c), $m^{ {\mathrm{ t \bar{t} } } }$ (d), and $y^{ {\mathrm{ t \bar{t} } } }$ (e) of the top-quark pairs. The inner (outer) error bars indicate the statistical (combined statistical and systematic) uncertainty. The measurements are compared to predictions from MadGraph +PYTHIA , POWHEG +PYTHIA , MC@NLO+HERWIG, and to an approximate NNLO calculation [8], when available. The MadGraph +PYTHIA prediction is shown both as a curve and as a binned histogram.
png pdf	Figure 6-d: Normalised differential ${\mathrm{ t \bar{t} } }$ production cross section as a function of the ${p_{\mathrm {T}}} ^{\text {t}}$ (a) and $y^{\text {t}}$ (b) of the top quarks or antiquarks, the ${p_{\mathrm {T}}} ^{ {\mathrm{ t \bar{t} } } }$ (c), $m^{ {\mathrm{ t \bar{t} } } }$ (d), and $y^{ {\mathrm{ t \bar{t} } } }$ (e) of the top-quark pairs. The inner (outer) error bars indicate the statistical (combined statistical and systematic) uncertainty. The measurements are compared to predictions from MadGraph +PYTHIA , POWHEG +PYTHIA , MC@NLO+HERWIG, and to an approximate NNLO calculation [8], when available. The MadGraph +PYTHIA prediction is shown both as a curve and as a binned histogram.
png pdf	Figure 6-e: Normalised differential ${\mathrm{ t \bar{t} } }$ production cross section as a function of the ${p_{\mathrm {T}}} ^{\text {t}}$ (a) and $y^{\text {t}}$ (b) of the top quarks or antiquarks, the ${p_{\mathrm {T}}} ^{ {\mathrm{ t \bar{t} } } }$ (c), $m^{ {\mathrm{ t \bar{t} } } }$ (d), and $y^{ {\mathrm{ t \bar{t} } } }$ (e) of the top-quark pairs. The inner (outer) error bars indicate the statistical (combined statistical and systematic) uncertainty. The measurements are compared to predictions from MadGraph +PYTHIA , POWHEG +PYTHIA , MC@NLO+HERWIG, and to an approximate NNLO calculation [8], when available. The MadGraph +PYTHIA prediction is shown both as a curve and as a binned histogram.

Summary

A measurement of normalised differential top-quark pair production cross sections in pp collisions at

$\sqrt{s} =$ 8 TeV with the CMS detector is presented. The measurement is performed in the dilepton (

$\mathrm{e^+e^-}$ ,

$\mu^+\mu^-$ , and

$\mu^{\pm}\mathrm{e^{\mp}}$ )

$\mathrm{ t \bar{t} }$ decay channels. The normalised

$\mathrm{ t \bar{t} }$ cross section is measured as a function of the transverse momentum, (pseudo)rapidity, and invariant mass of the final-state leading and next-to-leading leptons and b jets in the visible phase space, and of the top quarks (including the leading and next-to-leading top quarks) and

$\mathrm{ t \bar{t} }$ system in the full phase space. The measurements are in agreement with each other and with standard model predictions. The prediction at approximate NNLO precision is found to give a particularly good description of the top-quark transverse momentum.

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