CMS-PAS-TOP-16-015

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
CMS Collaboration
June 2016

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.
Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ;

Figures & Tables	Summary	Additional Figures	References	CMS Publications

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