CMS-TOP-17-018

CMS-TOP-17-018 ; CERN-EP-2018-074
Measurement of the production cross section for single top quarks in association with W bosons in proton-proton collisions at $\sqrt{s} =$ 13 TeV
CMS Collaboration
18 May 2018
JHEP 10 (2018) 117
Abstract: A measurement is presented of the associated production of a single top quark and a W boson in proton-proton collisions at $\sqrt{s} =$ 13 TeV by the CMS Collaboration at the CERN LHC. The data collected corresponds to an integrated luminosity of 35.9 fb $^{-1}$ . The measurement is performed using events with one electron and one muon in the final state along with at least one jet originated from a bottom quark. A multivariate discriminant, exploiting the kinematic properties of the events, is used to separate the signal from the dominant $\mathrm{t\bar{t}}$ background. The measured cross section of 63.1 $\pm$ 1.8 (stat) $\pm$ 6.4 (syst) $\pm$ 2.1 (lumi) pb is in agreement with the standard model expectation.
Links: e-print arXiv:1805.07399 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ;

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Leading-order Feynman diagrams for single top quark production in the tW channel that implicitly include the charge-conjugate contributions.
png pdf	Figure 1-a: Leading-order Feynman diagram for single top quark production in the tW channel that implicitly include the charge-conjugate contributions.
png pdf	Figure 1-b: Leading-order Feynman diagram for single top quark production in the tW channel that implicitly include the charge-conjugate contributions.
png pdf	Figure 2: Comparison of several lepton kinematic variables for the observed data and simulated events after the dilepton selection is applied. The last bin includes overflow events. The error band includes the statistical and all systematic uncertainties, except those from background normalization. The bottom of each panel shows the ratios of data to the sum of the expected yields.
png pdf	Figure 2-a: Comparison of the leading lepton $p_{\mathrm{T}}$ for the observed data and simulated events after the dilepton selection is applied. The last bin includes overflow events. The error band includes the statistical and all systematic uncertainties, except those from background normalization. The bottom of the panel shows the ratios of data to the sum of the expected yields.
png pdf	Figure 2-b: Comparison of the subleading lepton $p_{\mathrm{T}}$ for the observed data and simulated events after the dilepton selection is applied. The last bin includes overflow events. The error band includes the statistical and all systematic uncertainties, except those from background normalization. The bottom of the panel shows the ratios of data to the sum of the expected yields.
png pdf	Figure 2-c: Comparison of the leading lepton $\| \eta \|$ for the observed data and simulated events after the dilepton selection is applied. The last bin includes overflow events. The error band includes the statistical and all systematic uncertainties, except those from background normalization. The bottom of the panel shows the ratios of data to the sum of the expected yields.
png pdf	Figure 2-d: Comparison of the subleading lepton $\| \eta \|$ for the observed data and simulated events after the dilepton selection is applied. The last bin includes overflow events. The error band includes the statistical and all systematic uncertainties, except those from background normalization. The bottom of the panel shows the ratios of data to the sum of the expected yields.
png pdf	Figure 2-e: Comparison of the dilepton $p_{\mathrm{T}}$ for the observed data and simulated events after the dilepton selection is applied. The last bin includes overflow events. The error band includes the statistical and all systematic uncertainties, except those from background normalization. The bottom of the panel shows the ratios of data to the sum of the expected yields.
png pdf	Figure 2-f: Comparison of $M_{\mathrm{e}^{\pm}\mu^{\mp}}$ for the observed data and simulated events after the dilepton selection is applied. The last bin includes overflow events. The error band includes the statistical and all systematic uncertainties, except those from background normalization. The bottom of the panel shows the ratios of data to the sum of the expected yields.
png pdf	Figure 3: Yields observed in data, compared with those expected from simulation, as a function of the number of jets and number of b-tagged jets for events passing the baseline dilepton selection. The error band includes the statistical and all systematic uncertainties, except those from background normalization. The bottom of each panel shows the ratios of data to the sum of the expected yields.
png pdf	Figure 4: Most discriminating variables used for the training of the BDT in the 1j1b category. The last bin includes overflow events. The error band includes the statistical and all systematic uncertainties. The bottom of each panel shows the ratios of data to the sum of the expected yields.
png pdf	Figure 4-a: Loose jet $p_{\mathrm{T}}$ . The last bin includes overflow events. The error band includes the statistical and all systematic uncertainties. The bottom of the panel shows the ratios of data to the sum of the expected yields.
png pdf	Figure 4-b: $p_{\mathrm{T}}^{\text{sys}}$ . The last bin includes overflow events. The error band includes the statistical and all systematic uncertainties. The bottom of the panel shows the ratios of data to the sum of the expected yields.
png pdf	Figure 4-c: Leading jet $p_{\mathrm{T}}$ . The last bin includes overflow events. The error band includes the statistical and all systematic uncertainties. The bottom of the panel shows the ratios of data to the sum of the expected yields.
png pdf	Figure 4-d: $( p_{\mathrm{T}}(\mathrm{e})+p_{\mathrm{T}}(\mu) )/H_{\mathrm{T}}$ . The last bin includes overflow events. The error band includes the statistical and all systematic uncertainties. The bottom of the panel shows the ratios of data to the sum of the expected yields.
png pdf	Figure 5: Comparison of the BDT output in the 1j1b (upper left) and 2j1b (upper right) regions and the ${p_{\mathrm {T}}}$ of the subleading jet in the 2j2b region (lower) distributions after the fit is performed for the observed data and simulated events. The error band includes the statistical and systematic uncertainties. The bottom of each panel shows the ratios of data to the prediction from simulations and from the fit.
png pdf	Figure 5-a: Comparison of the BDT output in the 1j1b region, after the fit is performed for the observed data and simulated events. The error band includes the statistical and systematic uncertainties. The bottom of the panel shows the ratios of data to the prediction from simulations and from the fit.
png pdf	Figure 5-b: Comparison of the BDT output in the 2j1b region, after the fit is performed for the observed data and simulated events. The error band includes the statistical and systematic uncertainties. The bottom of the panel shows the ratios of data to the prediction from simulations and from the fit.
png pdf	Figure 5-c: Distribution of the ${p_{\mathrm {T}}}$ of the subleading jet in the 2j2b region, after the fit is performed for the observed data and simulated events. The error band includes the statistical and systematic uncertainties. The bottom of the panel shows the ratios of data to the prediction from simulations and from the fit.

Tables
png pdf	Table 1: Number of expected prefit and postfit signal and ${{\mathrm {t}\overline {\mathrm {t}}}}$ background events.
png pdf	Table 2: Estimation of the effect on the signal strength of each source of uncertainty in the fit. Experimental and modeling uncertainties affect both the rate and the shape of the templates while background normalization uncertainties affect only the rate.

Summary

The data recorded by CMS at 13 TeV, corresponding to an integrated luminosity of 35.9

$\pm$ 0.9 fb

$^{-1}$ , are used to measure the tW production cross section in the

${\mathrm{e^{\pm}}\mu^{\mp}}$ channel, classifying the events in terms of the number of jets and jets originating from bottom quarks. The signal is measured using a maximum likelihood fit to the distribution of boosted decision tree discriminants in two of the categories, and to the

${p_{\mathrm{T}}}$ distribution of the second jet with highest

${p_{\mathrm{T}}}$ in a third category. The measured cross section for tW production is found to be 63.1

$\pm$ 1.8 (stat)

$\pm$ 6.4 (syst)

$\pm$ 2.1 (lumi) pb, achieving a relative uncertainty of 11%. This is the first measurement of this process by the CMS Collaboration at

$\sqrt{s} =$ 13 TeV. The measured cross section is in agreement with the standard model prediction of 71.7

$\pm$ 1.8 (scale)

$\pm$ 3.4 (PDF) pb and with a similar measurement by the ATLAS Collaboration [13].

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