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| CMS-PAS-TOP-16-023 | ||
| Measurement of the inclusive $\mathrm{t\overline{t}}$ cross section at $\sqrt{s} = $ 5.02 TeV | ||
| CMS Collaboration | ||
| April 2017 | ||
| Abstract: The top quark pair production cross section is measured is measured in pp collisions at a center-of-mass energy $\sqrt{s} = $ 5.02 TeV. The analyzed data have been collected by the CMS experiment at the CERN LHC and correspond to an integrated luminosity of 27.4 pb$^{-1}$. The measurement is performed by analyzing events with at least one charged lepton. The measured cross section is $\sigma_{\rm{t\bar t}} = $ 69.5 $\pm$ 8.4 pb, in agreement with the expectation from the standard model. The impact of the presented measurement on the gluon distribution function is illustrated through a QCD analysis at next-to-next-to leading order. | ||
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Links:
CDS record (PDF) ;
inSPIRE record ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, JHEP 03 (2018) 115. The superseded preliminary plots can be found here. |
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| Figures | |
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Figure 1:
Distribution of the $M( \mathrm{j,\, j' } )$ variable for $\ell $+jets events in 0b- (left), 1b- (center) and $\geq $ 2b- (right) jet categories. The distributions observed in the data are compared to the sum of the expectations for the signal and backgrounds prior to any fit. The QCD multijet background is estimated from data (cf. Section 5.1). The shaded band represents the statistical and integrated luminosity uncertainties on the expected signal and background yields. |
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Figure 1-a:
Distribution of the $M( \mathrm{j,\, j' } )$ variable for $\ell $+jets events in the 0b-jet category. The distribution observed in the data is compared to the sum of the expectations for the signal and backgrounds prior to any fit. The QCD multijet background is estimated from data (cf. Section 5.1). The shaded band represents the statistical and integrated luminosity uncertainties on the expected signal and background yields. |
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Figure 1-b:
Distribution of the $M( \mathrm{j,\, j' } )$ variable for $\ell $+jets events in the 1b-jet category. The distribution observed in the data is compared to the sum of the expectations for the signal and backgrounds prior to any fit. The QCD multijet background is estimated from data (cf. Section 5.1). The shaded band represents the statistical and integrated luminosity uncertainties on the expected signal and background yields. |
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Figure 1-c:
Distribution of the $M( \mathrm{j,\, j' } )$ variable for $\ell $+jets events in the $\geq $ 2b-jet category. The distribution observed in the data is compared to the sum of the expectations for the signal and backgrounds prior to any fit. The QCD multijet background is estimated from data (cf. Section 5.1). The shaded band represents the statistical and integrated luminosity uncertainties on the expected signal and background yields. |
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Figure 2:
Distribution of the $\text{min}\Delta R( \mathrm{ j,\, j' } )$ variable for $\ell $+jets events in 0b- (left), 1b- (center) and $\geq $ 2b- (right) jet categories. The distributions observed in the data are compared to the sum of the expectations for the signal and backgrounds prior to any fit. The QCD multijet background is estimated from data (cf. Section 5.1). The shaded band represents the statistical and integrated luminosity uncertainties on the expected signal and background yields. |
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Figure 2-a:
Distribution of the $\text{min}\Delta R( \mathrm{ j,\, j' } )$ variable for $\ell $+jets events in the 0b-jet category. The distribution observed in the data is compared to the sum of the expectations for the signal and backgrounds prior to any fit. The QCD multijet background is estimated from data (cf. Section 5.1). The shaded band represents the statistical and integrated luminosity uncertainties on the expected signal and background yields. |
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Figure 2-b:
Distribution of the $\text{min}\Delta R( \mathrm{ j,\, j' } )$ variable for $\ell $+jets events in the 1b-jet category. The distribution observed in the data is compared to the sum of the expectations for the signal and backgrounds prior to any fit. The QCD multijet background is estimated from data (cf. Section 5.1). The shaded band represents the statistical and integrated luminosity uncertainties on the expected signal and background yields. |
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Figure 2-c:
Distribution of the $\text{min}\Delta R( \mathrm{ j,\, j' } )$ variable for $\ell $+jets events in the $\geq $ 2b- jet category. The distribution observed in the data is compared to the sum of the expectations for the signal and backgrounds prior to any fit. The QCD multijet background is estimated from data (cf. Section 5.1). The shaded band represents the statistical and integrated luminosity uncertainties on the expected signal and background yields. |
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Figure 3:
Left: the 68% CL contour obtained from the scan of the likelihood, as function of the signal strength and the b-tagging scale factor in the l+jets analysis. The solid (dashed) contours represent the contours observed in data (expected from simulation). The solid (hollow) point represents the observed fit result (SM expectation). Right: summary of the signal strengths separately obtained in the $\mu$+jets and the e+jets channel, and after their combination in the $\ell$+jets channel. The results of the analysis from the distributions (Distr.) are compared to those of a cross-check analysis based on event counting (Count). The inner (outer) bars correspond to the statistical (total) uncertainty of the signal strengths. Bands represent the total uncertainty of the signal strengths in the $\ell$+jets channel. |
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Figure 3-a:
The 68% CL contour obtained from the scan of the likelihood, as function of the signal strength and the b-tagging scale factor in the l+jets analysis. The solid (dashed) contours represent the contours observed in data (expected from simulation). The solid (hollow) point represents the observed fit result (SM expectation). |
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Figure 3-b:
Summary of the signal strengths separately obtained in the $\mu$+jets and the e+jets channel, and after their combination in the $\ell$+jets channel. The results of the analysis from the distributions (Distr.) are compared to those of a cross-check analysis based on event counting (Count). The inner (outer) bars correspond to the statistical (total) uncertainty of the signal strengths. Bands represent the total uncertainty of the signal strengths in the $\ell$+jets channel. |
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Figure 4:
Distributions of the jet multiplicity (left), and scalar ${p_{\mathrm {T}}}$ sum of all jets (right) in events passing the dilepton pair criteria in the ${\mathrm{ e } ^\pm \mu ^\mp }$ channel. The Z/$\gamma ^{*}$ and Non-W/Z backgrounds are determined from data (cf. Section xxx). The shaded band represents the statistical and integrated luminosity uncertainties on the expected signal and background yields. The last bin of the distributions contains the overflow events. |
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Figure 4-a:
Distribution of the jet multiplicity in events passing the dilepton pair criteria in the ${\mathrm{ e } ^\pm \mu ^\mp }$ channel. The Z/$\gamma ^{*}$ and Non-W/Z backgrounds are determined from data (cf. Section 5.2). The shaded band represents the statistical and integrated luminosity uncertainties on the expected signal and background yields. The last bin of the distributions contains the overflow events. |
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Figure 4-b:
Distribution of the scalar ${p_{\mathrm {T}}}$ sum of all jets in events passing the dilepton pair criteria in the ${\mathrm{ e } ^\pm \mu ^\mp }$ channel. The Z/$\gamma ^{*}$ and Non-W/Z backgrounds are determined from data (cf. Section 5.2). The shaded band represents the statistical and integrated luminosity uncertainties on the expected signal and background yields. The last bin of the distributions contains the overflow events. |
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Figure 5:
Distributions of the invariant mass (left) and ${p_{\mathrm {T}}}$ (right) of the dilepton pair after requiring at least two jets in the ${\mathrm{ e } ^\pm \mu ^\mp }$ channel. The Z/$\gamma ^{*}$ and Non-W/Z backgrounds are determined from data (cf. Section 5.2). The shaded band represents the statistical and integrated luminosity uncertainties on the expected signal and background yields. The last bin of the distributions contains the overflow events. |
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Figure 5-a:
Distribution of the invariant mass of the dilepton pair after requiring at least two jets in the ${\mathrm{ e } ^\pm \mu ^\mp }$ channel. The Z/$\gamma ^{*}$ and Non-W/Z backgrounds are determined from data (cf. Section 5.2). The shaded band represents the statistical and integrated luminosity uncertainties on the expected signal and background yields. The last bin of the distributions contains the overflow events. |
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Figure 5-b:
Distribution of the ${p_{\mathrm {T}}}$ of the dilepton pair after requiring at least two jets in the ${\mathrm{ e } ^\pm \mu ^\mp }$ channel. The Z/$\gamma ^{*}$ and Non-W/Z backgrounds are determined from data (cf. Section 5.2). The shaded band represents the statistical and integrated luminosity uncertainties on the expected signal and background yields. The last bin of the distributions contains the overflow events. |
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Figure 6:
Distributions of the missing transverse momentum (left) in events passing the dilepton criteria and Z veto, and invariant mass (right) of the dilepton pair after the missing transverse momentum requirement in the ${\mu ^\pm \mu ^\mp } $ channel. The shaded band represents the statistical and integrated luminosity uncertainties on the expected signal and background yields. The last bin of the distributions contains the overflow events. |
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Figure 6-a:
Distribution of the missing transverse momentum in events passing the dilepton criteria and Z veto. The shaded band represents the statistical and integrated luminosity uncertainties on the expected signal and background yields. The last bin of the distributions contains the overflow events. |
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Figure 6-b:
Invariant mass of the dilepton pair after the missing transverse momentum requirement in the ${\mu ^\pm \mu ^\mp } $ channel. The shaded band represents the statistical and integrated luminosity uncertainties on the expected signal and background yields. The last bin of the distributions contains the overflow events. |
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Figure 7:
Top quark pair production cross section in $\mathrm{ p \bar{p} } $ and $ \mathrm{ pp } $ collisions as a function of the center-of-mass energy; the Tevatron combination at ${\sqrt {s}} = $ 1.96 TeV is displayed, as well as CMS results at 7, 8 and 13 TeV in the dilepton and $\ell $+jets channel. The measurements are compared to the NNLO+NNLL theory predictions. |
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Figure 8:
The gluon distribution as functions of $x$ at the scale of 100000 GeV$^2$. The results of the fit including top-quark measurements (shaded band), and without those (hatched band) are compared. The fit uncertainties as obtained by using the MC method,are shown. In the bottom panel, the relative fractional uncertainties are presented. |
| Tables | |
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Table 1:
Basic selection criteria applied in the three final states considered in this analysis. |
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Table 2:
Expected and observed event yields in the different categories used in the $\ell $+jets analysis, prior to the fit. With the exception of the QCD multijet estimate, for which the total uncertainty is reported, the uncertainties reflect the limited statistics in the simulations. |
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Table 3:
Estimated impact of each source of uncertainty on the analysis of distributions and on the cross-check from event counting. ``Other backgrounds'' contains the residual contribution from Z/$\gamma ^{*}$, tW and WV events. The total uncertainty is obtained by adding in quadrature statistical, systematic and theory uncertainties. The values quoted have been symmetrized. |
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Table 4:
Number of dilepton events obtained after applying the full selection. The results are given for the individual sources of background, ${\mathrm{ t } {}\mathrm{ \bar{t} } }$ signal, and data. The uncertainties correspond to statistical and systematic components. |
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Table 5:
Summary of individual contributions to the systematic uncertainty on the $\sigma _{{\mathrm{ t } {}\mathrm{ \bar{t} } } }$ measurement in the dilepton channel. The absolute uncertainties $\Delta \sigma _{{\mathrm{ t } {}\mathrm{ \bar{t} } } }$ in pb as well as relative uncertainties ($\Delta \sigma _{{\mathrm{ t } {}\mathrm{ \bar{t} } } } /\sigma _{{\mathrm{ t } {}\mathrm{ \bar{t} } } }$) are given. |
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Table 6:
Partial $\chi ^2$ per number of data points, $n_{\textrm {dp}}$, and the global $\chi ^2$ per degrees of freedom, $n_{\text {dof}}$, as obtained in the QCD analysis of DIS data, the CMS muon charge asymmetry and the inclusive cross sections of top-quark pair production at $\sqrt {s} = $ 5.02 TeV. For HERA measurements, the energy of the proton beam is listed for each data set, with electron energy being $E_{\mathrm{ e } }= $ 27.5 GeV. |
| Summary |
| In summary, the first measurement of the $ \mathrm{ t \bar{t} }$ production cross section in pp collisions at ${\sqrt{s}} = $ 5.02 TeV is presented for events with one or two leptons and at least two jets using a data sample corresponding to an integrated luminosity of 27.4 pb$^{-1}$. The final measurement is obtained as the combination of the measurements in the individual channels. The result is 69.5 pb, with a total relative uncertainty of 12%, which is consistent with the SM prediction. The impact of the measured $\mathrm{ t \bar{t} }$ cross section on the proton PDFs is studied in a QCD analysis at NNLO and a moderate decrease of the uncertainty in the gluon distribution at high fractions $x$ of the proton momentum carried by the gluon is observed. |
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