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CMS-PAS-TOP-16-015
First measurement of the top quark pair production cross section in proton-proton collisions at $\sqrt{s}=$ 5.02 TeV
Abstract: The top quark pair production cross section is measured for the first time in proton-proton collisions at $\sqrt{s} =$ 5.02 TeV using data corresponding to an integrated luminosity of 26 pb$^{-1}$. The measurement is performed by analyzing events with at least one electron and one muon of opposite charge, and at least two jets. The measured cross section is $\sigma_{t\bar t} =$ 82 $\pm$ 20 (stat) $\pm$ 5 (syst) $\pm$ 10 (lumi) pb, in agreement with the expectation from the standard model.
Figures & Tables Summary Additional Figures References CMS Publications
Figures

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Figure 1-a:
Distributions of the jet multiplicity (a), and scalar ${p_{\mathrm {T}}}$ sum of all jets (b) in events passing the dilepton criteria. The DY and Non W/Z backgrounds are determined from data. The last bin of the distributions contains the overflow events.

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Figure 1-b:
Distributions of the jet multiplicity (a), and scalar ${p_{\mathrm {T}}}$ sum of all jets (b) in events passing the dilepton criteria. The DY and Non W/Z backgrounds are determined from data. The last bin of the distributions contains the overflow events.

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Figure 2-a:
Distributions of the invariant mass (a) and ${p_{\mathrm {T}}}$ (b) of the dilepton after requiring at least two jets in the event. The DY and Non W/Z backgrounds are determined from data. The last bin of the distributions contains the overflow events.

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Figure 2-b:
Distributions of the invariant mass (a) and ${p_{\mathrm {T}}}$ (b) of the dilepton after requiring at least two jets in the event. The DY and Non W/Z backgrounds are determined from data. The last bin of the distributions contains the overflow events.

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Figure 3:
Top quark pair production cross section in $\mathrm{ p \bar{p} }$ and $\mathrm{pp}$ collisions as a function of the centre-of-mass energy; the Tevatron combination at $\sqrt {s}= $ 1.96 TeV is displayed, as well as CMS results at 7, 8 and 13TeV in the dilepton channel. The measurements are compared to the NNLO+NNLL theory predictions.
Tables

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Table 1:
Selection criteria applied in the analysis. Note that electron candidates between the barrel and endcap sections of ECAL are excluded.

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Table 2:
Summary of individual contributions to the systematic uncertainty on the $\sigma _{ \mathrm {t \bar{t} } }$ measurement. The absolute uncertainties $\Delta \sigma _{ \mathrm {t \bar{t} } }$ are given in pb, as well as relative uncertainties ($\Delta \sigma _{ \mathrm {t \bar{t} } } /\sigma _{ \mathrm {t \bar{t} } }$). The separate total systematic uncertainty without integrated luminosity, the part attributed to the integrated luminosity, and the statistical contribution are added in quadrature to obtain the total uncertainty.

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Table 3:
The number of ${\mathrm{ e } ^\pm \mu ^\mp }$ events after final event selection expected for background and signal, and observed in data. The uncertainties represent only the statistical component.
Summary
In summary, the first measurement of the $\mathrm{ t \bar{t} }$ production cross section in proton-proton collisions at $\sqrt{s} =$ 5.02 TeV is presented for events containing an electron-muon pair and at least two jets. The measurement is obtained through an event-counting analysis based on a data sample corresponding to an integrated luminosity of 26 $\pm$ 3 pb$^{-1}$. The result is 82 pb, with a total relative uncertainty of 28%. This measurement is consistent with the SM prediction.
Additional Figures

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Additional Figure 1:
Initial partonic states yielding $\mathrm{ t \bar{t} }$ pairs in pp collisions at $\sqrt {s}= $ 5.02 TeV simulated at NLO with POWHEG and the NNPDF3.0 PDF set. The fraction (in %) of each initial state is represented.

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Additional Figure 2:
Expected average momentum of the incoming partons measured with respect to the proton momentum, for collisions at $\sqrt {s}= $ 5.02 TeV and 13 TeV, as simulated by POWHEG and the NNPDF3.0 set.

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Additional Figure 3:
Average momentum transfer in the partonic collision yielding a $\mathrm{ t \bar{t} }$ pair for collisions at $\sqrt {s}= $ 5.02 TeV and 13 TeV, as simulated by POWHEG and the NNPDF3.0 set.

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Additional Figure 4:
Event display of a candidate $\mathrm{ t \bar{t} }$ event selected in the $\sqrt {s}= $ 5.02 TeV dataset recorded by CMS. The figure depicts the CMS sub-detectors in the $\rho$-$\phi $ plane. Calorimetric energy deposits in ECAL (HCAL) are depicted as red (blue) bars with a height proportional to the magnitude of the deposit. Tracks are represented by green (red) lines if reconstructed from tracker (tracker+muon system) hits. The measured kinematics of the reconstructed electron, muon, jets and missing transverse energy ($ E_{\mathrm{T}}^{\text{miss}} $) are represented next to each object.
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