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| CMS-SMP-14-020 ; CERN-EP-2016-190 | ||
| Measurement of the production cross section of a W boson in association with two b jets in pp collisions at $ \sqrt{s} = $ 8 TeV | ||
| CMS Collaboration | ||
| 26 August 2016 | ||
| EPJC 77 (2017) 92 | ||
| Abstract: The production cross section of a W boson in association with two b jets is measured using a sample of proton-proton collisions at $ \sqrt{s} = $ 8 TeV collected by the CMS experiment at the CERN LHC. The data sample corresponds to an integrated luminosity of 19.8 fb$^{-1}$. The W bosons are reconstructed via their leptonic decays, $ \mathrm{ W }\to\ell\nu $, where $\ell=\mu$ or $\mathrm{ e }$. The fiducial region studied contains exactly one lepton with transverse momentum $ p_{\mathrm{T}}^{\ell} > $ 30 GeV and pseudorapidity $ | {\eta^{\ell}} | < $ 2.1, with exactly two b jets with $ p_{\mathrm{T}} > $ 25 GeV and $ | {\eta} | < $ 2.4 and no other jets with $ p_{\mathrm{T}} > $ 25 GeV and $ | {\eta} | < $ 4.7. The cross section is measured to be $ \sigma ( {{\mathrm{ p }\mathrm{ p }}} \to {\mathrm{ W }} (\ell\nu) + \mathrm{ b \bar{b} }) =$ 0.64 $\pm$ 0.03 (stat) $\pm$ 0.10 (syst) $\pm$ 0.06 (theory) $\pm$ 0.02 (lumi) pb, in agreement with standard model predictions. | ||
| Links: e-print arXiv:1608.07561 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
The transverse mass distributions (upper) in the $ {\mathrm{ t } {}\mathrm{ \bar{t} } } $-multijet phase space after fitting to obtain the b tagging efficiency rescale factors, (middle) in the $ {\mathrm{ t } {}\mathrm{ \bar{t} } } $-multilepton sample after fitting to find the appropriate JES, and (lower) in the $ \mathrm{ W } + {\mathrm{ b \bar{b} } }$ signal sample after fitting simultaneously muon and electron decay channels. The lepton channels are shown separately with the muon sample on the left and the electron sample on the right. The last bin contains overflow events. The shaded area represents the total uncertainty in the simulation after the fit. |
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Figure 1-a:
The transverse mass distributions in the $ {\mathrm{ t } {}\mathrm{ \bar{t} } } $-multijet phase space after fitting to obtain the b tagging efficiency rescale factors, muon sample. The last bin contains overflow events. The shaded area represents the total uncertainty in the simulation after the fit. |
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Figure 1-b:
The transverse mass distributions in the $ {\mathrm{ t } {}\mathrm{ \bar{t} } } $-multijet phase space after fitting to obtain the b tagging efficiency rescale factors, electron sample. The last bin contains overflow events. The shaded area represents the total uncertainty in the simulation after the fit. |
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Figure 1-c:
The transverse mass distributions in the $ {\mathrm{ t } {}\mathrm{ \bar{t} } } $-multilepton sample after fitting to find the appropriate JES, muon sample. The last bin contains overflow events. The shaded area represents the total uncertainty in the simulation after the fit. |
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Figure 1-d:
The transverse mass distributions in the $ {\mathrm{ t } {}\mathrm{ \bar{t} } } $-multilepton sample after fitting to find the appropriate JES, electron sample. The last bin contains overflow events. The shaded area represents the total uncertainty in the simulation after the fit. |
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Figure 1-e:
The transverse mass distributions in the $ \mathrm{ W } + {\mathrm{ b \bar{b} } }$ signal sample after fitting simultaneously muon and electron decay channels, muon sample. The last bin contains overflow events. The shaded area represents the total uncertainty in the simulation after the fit. |
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Figure 1-f:
The transverse mass distributions in the $ \mathrm{ W } + {\mathrm{ b \bar{b} } }$ signal sample after fitting simultaneously muon and electron decay channels, electron sample. The last bin contains overflow events. The shaded area represents the total uncertainty in the simulation after the fit. |
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Figure 2:
Distributions of $\Delta R(\mathrm{ b } ,\mathrm{ \bar{b} } )$ and $ {p_{\mathrm {T}}} ^\ell $ after applying the results from the fits to the simulation. The QCD background shape is taken from an $ {M_\mathrm {T}} < $ 30 GeV sideband and the muon and electron channels have been combined in these distributions. The last bin contains overflow events and the shaded area represents the total uncertainty in the simulation after the fit. |
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Figure 2-a:
Distribution of $\Delta R(\mathrm{ b } ,\mathrm{ \bar{b} } )$ after applying the results from the fits to the simulation. The QCD background shape is taken from an $ {M_\mathrm {T}} < $ 30 GeV sideband and the muon and electron channels have been combined in these distributions. The last bin contains overflow events and the shaded area represents the total uncertainty in the simulation after the fit. |
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Figure 2-b:
Distributions of $ {p_{\mathrm {T}}} ^\ell $ after applying the results from the fits to the simulation. The QCD background shape is taken from an $ {M_\mathrm {T}} < $ 30 GeV sideband and the muon and electron channels have been combined in these distributions. The last bin contains overflow events and the shaded area represents the total uncertainty in the simulation after the fit. |
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Figure 3:
Comparison between the measured $ {\mathrm{ W } (\ell \nu )}+ {\mathrm{ b \bar{b} } } $ cross section and various QCD predictions. The orange band indicates the uncertainty in the given sample associated with PDF choice and the yellow band represents the uncertainty associated with DPI. The labels 4F and 5F refer to the four- and five-flavour PDF schemes. In the case of the MadGraph + PYTHIA-6 (5F) sample, the effects of DPI are already included in the generated samples so the DPI correction is not needed. The measured cross section is also shown with the total uncertainty in black and the luminosity, statistical, theoretical, and systematic uncertainties indicated. |
| Tables | |
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Table 1:
The main sources of systematic uncertainty in the $ \mathrm{ W } + {\mathrm{ b \bar{b} } } $ signal event sample. The column labeled ``Variation'' indicates the bounds on the normalization change of a given sample due to a variation of the uncertainty by one standard deviation. The last column indicates the contribution of the given systematic to the overall uncertainty in the measured cross section. The uncertainty labeled ``b tag eff rescaling'' is the uncertainty associated with the rescaling of the b tagging efficiency. UES refers to the scale of energy deposits not clustered into jets, and MES and EES refer to the muon and electron energy scales. The uncertainty labeled as "Id/Iso/Trg" is the uncertainty associated with the efficiency of the lepton identification, isolation, and trigger. The uncertainties in the integrated luminosity [14] and in the acceptance due to PDF uncertainties and scale choices are not included in the fit, and are treated separately. |
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Table 2:
Initial and final yields obtained in the $ \mathrm{ W } + {\mathrm{ b \bar{b} } } $ signal region. The uncertainties in the signal strength represent the total uncertainty of the fit. |
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Table 3:
Measured cross sections in the muon, electron, and combined lepton channels. |
| Summary |
| The cross section for the production of a W boson in association with two b jets was measured using a sample of proton-proton collisions at $ \sqrt{s} = $ 8 TeV collected by the CMS experiment. The data sample corresponds to an integrated luminosity of 19.8 fb$^{-1}$. The W bosons were reconstructed via their leptonic decays, $ \mathrm{ W }\to\ell\nu $, where $\ell=\mu$ or $\mathrm{ e }$. The fiducial region studied contains exactly one lepton with transverse momentum $ p_{\mathrm{T}}^{\ell} > $ 30 GeV and pseudorapidity $ | {\eta^{\ell}} | < $ 2.1, with exactly two b jets with $ p_{\mathrm{T}} > $ 25 GeV and $ | {\eta} | < $ 2.4 and no other jets with $ p_{\mathrm{T}} > $ 25 GeV and $ | {\eta} | < $ 4.7. The cross section is $ \sigma ( {{\mathrm{ p }\mathrm{ p }}} \to {\mathrm{ W }} (\ell\nu)+\mathrm{ b \bar{b} }) = $ 0.64 $\pm$ 0.03 (stat) $\pm$ 0.10 (syst) $\pm$ 0.06 (theory) $\pm$ 0.02 (lumi) pb, in agreement with standard model predictions. |
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