CMS-PAS-SMP-17-014 | ||

Measurement of associated production of W bosons with charm quarks in proton-proton collisions at $\sqrt{s}= $ 13 TeV with the CMS experiment at the LHC | ||

CMS Collaboration | ||

April 2018 | ||

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Abstract:
Measurements are presented of the associated production of a W boson and a charm quark (W+c) in proton-proton collisions at a center-of-mass energy of 13 TeV. The data correspond to an integrated luminosity of 35.7 fb$^{-1}$, collected by the CMS experiment at the LHC. The W bosons are identified by their decays into a muon and a neutrino. The charm quarks are tagged through the full reconstruction of $\mathrm{D}^*(2010)^{\pm}$ mesons in their decays $\mathrm{D}^*(2010)^{\pm} \to \mathrm{D}^0 + \pi^{\pm}_{\text{slow}} \to \mathrm{K}^{\mp} + \pi^{\pm} + \pi^{\pm}_{\text{slow}}$. The measurements are performed for the transverse momentum of the muon from the W boson decay greater than 26 GeV in the pseudorapidity range $|\eta^{\mu}| < $ 2.4 and for transverse momentum of the charm quark greater than 5 GeV. The total cross section of $\sigma(\mathrm{W+c}) = $ 1026 $\pm$ 31 (stat) $^{+76}_{-72}$ (syst) pb is obtained. The cross sectionW+c is also measured differentially with respect to the absolute value of the pseudorapidity of the muon from the W boson decay. Results are compared with theoretical predictions and are used to probe the strange quark content of the proton.
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Links:
CDS record (PDF) ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, EPJC 79 (2019) 269.The superseded preliminary plots can be found here. |

Figures | |

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Figure 1:
Dominant contributions to W+c production at the LHC at leading order QCD. |

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Figure 1-a:
Dominant contribution to W+c production at the LHC at leading order QCD. |

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Figure 1-b:
Dominant contribution to W+c production at the LHC at leading order QCD. |

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Figure 2:
Distribution of the muon transverse momentum (left) and muon pseudorapidity (right). The data (filled circles) are compared to the MC simulation of contributions of different processes (filled bands of different color). |

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Figure 2-a:
Distribution of the muon transverse momentum. The data (filled circles) are compared to the MC simulation of contributions of different processes (filled bands of different color). |

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Figure 2-b:
Distribution of the muon pseudorapidity. The data (filled circles) are compared to the MC simulation of contributions of different processes (filled bands of different color). |

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Figure 3:
Distributions of missing transverse momentum (left) and of transverse mass (right). The data (filled circles) are compared to the MC simulation of contributions of different processes (filled bands of different color). |

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Figure 3-a:
Distribution of missing transverse momentum. The data (filled circles) are compared to the MC simulation of contributions of different processes (filled bands of different color). |

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Figure 3-b:
Distribution of transverse mass. The data (filled circles) are compared to the MC simulation of contributions of different processes (filled bands of different color). |

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Figure 4:
Distributions of the reconstructed invariant mass of $ {\mathrm {K}}^\pm \pi ^\mp $ candidates (left) in the range $| \Delta m(\mathrm{D}^*,\,\mathrm{D}^0) -145.45| < $ 1 MeV, and of the reconstructed mass difference $\Delta m(\mathrm{D}^*,\,\mathrm{D}^0)$ (right). The SS combinations are subtracted. The data (closed symbols) are compared to MC simulation with contributions from different processes shown as histograms of different shades. |

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Figure 4-a:
Distribution of the reconstructed invariant mass of $ {\mathrm {K}}^\pm \pi ^\mp $ candidates in the range $| \Delta m(\mathrm{D}^*,\,\mathrm{D}^0) -145.45| < $ 1 MeV. The SS combinations are subtracted. The data (closed symbols) are compared to MC simulation with contributions from different processes shown as histograms of different shades. |

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Figure 4-b:
Distribution of the reconstructed mass difference $\Delta m(\mathrm{D}^*,\,\mathrm{D}^0)$. The SS combinations are subtracted. The data (closed symbols) are compared to MC simulation with contributions from different processes shown as histograms of different shades. |

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Figure 5:
Number of events after OS-SS subtraction for the data (closed symbols) and MC simulation (filled histograms) as a function of $|\eta ^{{{\mu}}}|$. |

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Figure 6:
Inclusive cross section of $\sigma ( {\mathrm {W}}+ {\mathrm {c}})$ (left) and the cross section ratio for $\sigma ( {\mathrm {W^+}}+ {\overline {\mathrm {c}}})/\sigma ( {\mathrm {W^-}}+ {\mathrm {c}})$ (right) at 13 TeV. The data are represented by a line with the statistical (total) uncertainty shown by a light (dark) shaded band. The measurements are compared to the NLO QCD prediction using several PDF sets, represented by symbols of different types. The horizontal error bars depict the total theory uncertainty, including the PDF and the scale variation uncertainty. |

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Figure 6-a:
Inclusive cross section of $\sigma ( {\mathrm {W}}+ {\mathrm {c}})$ at 13 TeV. The data are represented by a line with the statistical (total) uncertainty shown by a light (dark) shaded band. The measurements are compared to the NLO QCD prediction using several PDF sets, represented by symbols of different types. The horizontal error bars depict the total theory uncertainty, including the PDF and the scale variation uncertainty. |

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Figure 6-b:
Cross section ratio for $\sigma ( {\mathrm {W^+}}+ {\overline {\mathrm {c}}})/\sigma ( {\mathrm {W^-}}+ {\mathrm {c}})$ at 13 TeV. The data are represented by a line with the statistical (total) uncertainty shown by a light (dark) shaded band. The measurements are compared to the NLO QCD prediction using several PDF sets, represented by symbols of different types. The horizontal error bars depict the total theory uncertainty, including the PDF and the scale variation uncertainty. |

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Figure 7:
Left: cross sections of $\sigma ( {\mathrm {W}}+ {\mathrm {c}})$ production at 13 TeV measured as a function of the pseudorapidity of the muon from the W boson decay. The data are presented by filled circles with the statistical (total) uncertainties shown by light (dark) shaded bands. The measurements are compared to the QCD predictions calculated with MCFM at NLO using different PDF sets, presented by symbols of different style. The horizontal error bars represent theory uncertainties including PDF uncertainty and the scale variation uncertainty. Right: $\sigma (\mathrm{W + D^*})$ production cross sections presented as a function of the pseudorapidity of the muon from the W boson decay. The data (closed symbols) are shown with their total (vertical error bars) and statistical uncertainties (inner error bars) and are compared to the predictions of the signal MC accounting for PDF uncertainties and scale variations, which are added in quadrature (shaded band). |

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Figure 7-a:
Cross sections of $\sigma ( {\mathrm {W}} + {\mathrm {c}})$ production at 13 TeV measured as a function of the pseudorapidity of the muon from the W boson decay. The data are presented by filled circles with the statistical (total) uncertainties shown by light (dark) shaded bands. The measurements are compared to the QCD predictions calculated with MCFM at NLO using different PDF sets, presented by symbols of different style. The horizontal error bars represent theory uncertainties including PDF uncertainty and the scale variation uncertainty. |

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Figure 7-b:
$\sigma (\mathrm{W + D^*})$ production cross sections presented as a function of the pseudorapidity of the muon from the W boson decay. The data (closed symbols) are shown with their total (vertical error bars) and statistical uncertainties (inner error bars) and are compared to the predictions of the signal MC accounting for PDF uncertainties and scale variations, which are added in quadrature (shaded band). |

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Figure 7-c:
Cross sections of $\sigma ( {\mathrm {W}}^{+} + \overline{\mathrm {c}})$ production at 13 TeV measured as a function of the pseudorapidity of the muon from the W boson decay. The data are presented by filled circles with the statistical (total) uncertainties shown by light (dark) shaded bands. The measurements are compared to the QCD predictions calculated with MCFM at NLO using different PDF sets, presented by symbols of different style. The horizontal error bars represent theory uncertainties including PDF uncertainty and the scale variation uncertainty. |

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Figure 7-d:
$\sigma (\mathrm{W^{+} + D^{*-}})$ production cross sections presented as a function of the pseudorapidity of the muon from the W boson decay. The data (closed symbols) are shown with their total (vertical error bars) and statistical uncertainties (inner error bars) and are compared to the predictions of the signal MC accounting for PDF uncertainties and scale variations, which are added in quadrature (shaded band). |

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Figure 7-e:
Cross sections of $\sigma ( {\mathrm {W}}^{-} + {\mathrm {c}})$ production at 13 TeV measured as a function of the pseudorapidity of the muon from the W boson decay. The data are presented by filled circles with the statistical (total) uncertainties shown by light (dark) shaded bands. The measurements are compared to the QCD predictions calculated with MCFM at NLO using different PDF sets, presented by symbols of different style. The horizontal error bars represent theory uncertainties including PDF uncertainty and the scale variation uncertainty. |

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Figure 7-f:
$\sigma (\mathrm{W^{-} + D^{*+}})$ production cross sections presented as a function of the pseudorapidity of the muon from the W boson decay. The data (closed symbols) are shown with their total (vertical error bars) and statistical uncertainties (inner error bars) and are compared to the predictions of the signal MC accounting for PDF uncertainties and scale variations, which are added in quadrature (shaded band). |

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Figure 8:
The s quark distribution (upper) and the strangeness suppression factor (lower) as functions of $x$ at the factorization scale of 1.9 GeV$^2$ (left) and $m^2_{{\mathrm {W}}}$ (right). The results of the current analysis are presented with the fit uncertainties estimated by Hessian method (hatched band) and using MC replicas (shaded band). |

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Figure 8-a:
The s quark distribution as a function of $x$ at the factorization scale of 1.9 GeV$^2$. The results of the current analysis are presented with the fit uncertainties estimated by Hessian method (hatched band) and using MC replicas (shaded band). |

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Figure 8-b:
The s quark distribution as a function of $m^2_{{\mathrm {W}}}$. The results of the current analysis are presented with the fit uncertainties estimated by Hessian method (hatched band) and using MC replicas (shaded band). |

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Figure 8-c:
The strangeness suppression factor as a function of $x$ at the factorization scale of 1.9 GeV$^2$. The results of the current analysis are presented with the fit uncertainties estimated by Hessian method (hatched band) and using MC replicas (shaded band). |

png pdf |
Figure 8-d:
The strangeness suppression factor as a function of $m^2_{{\mathrm {W}}}$. The results of the current analysis are presented with the fit uncertainties estimated by Hessian method (hatched band) and using MC replicas (shaded band). |

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Figure 9:
The strangeness suppression factor as a function of $x$ at the factorization scale of 1.9 GeV$^2$ (left) and $m^2_{{\mathrm {W}}}$ (right). The results of the current analysis (hatched band) are compared to ABMP16nlo (dark shaded band) and ATLASepWZ16nnlo (light shaded band) PDFs. |

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Figure 9-a:
The strangeness suppression factor as a function of $x$ at the factorization scale of 1.9 GeV$^2$. The results of the current analysis (hatched band) are compared to ABMP16nlo (dark shaded band) and ATLASepWZ16nnlo (light shaded band) PDFs. |

png pdf |
Figure 9-b:
The strangeness suppression factor as a function of $m^2_{{\mathrm {W}}}$. The results of the current analysis (hatched band) are compared to ABMP16nlo (dark shaded band) and ATLASepWZ16nnlo (light shaded band) PDFs. |

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Figure 10:
The distributions of s quark (upper panel) in the proton and its relative uncertainty (lower panel) as functions of $x$ at the factorization scale of 1.9 GeV$^2$ (left) and $m^2_{{\mathrm {W}}}$ (right). The result of the current analysis (filled band) is compared to the result of Ref. [11] (dashed band). The PDF uncertainties resulting from the fit are shown. |

png pdf |
Figure 10-a:
The distributions of s quark (upper panel) in the proton and its relative uncertainty (lower panel) as a function of $x$ at the factorization scale of 1.9 GeV$^2$. The result of the current analysis (filled band) is compared to the result of Ref. [11] (dashed band). The PDF uncertainties resulting from the fit are shown. |

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Figure 10-b:
The distributions of s quark (upper panel) in the proton and its relative uncertainty (lower panel) as a function of $m^2_{{\mathrm {W}}}$. The result of the current analysis (filled band) is compared to the result of Ref. [11] (dashed band). The PDF uncertainties resulting from the fit are shown. |

Tables | |

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Table 1:
Systematic uncertainties of the inclusive cross section and the five bins of $\eta ^{{{\mu}}}$ of the differential cross section of W+c in the fiducial range of the analysis. All contributions are in percent. The contributions listed above the gap cancel in the ratio $\sigma ( {\mathrm {W^+}}+ {\overline {\mathrm {c}}}) / \sigma ( {\mathrm {W^-}}+ {\mathrm {c}})$. |

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Table 2:
Inclusive cross sections of W+c and W+$\mathrm{D}^*$ production at ${\sqrt {s}}=$ 13 TeV in the fiducial range of the analysis. |

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Table 3:
Number of signal events, correction factors c and of the differential cross-sections in each $|\eta ^{{{\mu}}}|$ range for W+c (upper), $ {\mathrm {W^+}}+ {\overline {\mathrm {c}}}$ (middle) and $ {\mathrm {W^-}}+ {\mathrm {c}}$ (lower). |

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Table 4:
NLO predictions for $\sigma ( {\mathrm {W}}+ {\mathrm {c}})$. The uncertainties account for PDF and scale variations. |

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Table 5:
Theoretical predictions for $\mathrm{d}\sigma ( {\mathrm {W}}+ {\mathrm {c}})/\mathrm{d} |\eta ^\mu |$ calculated with MCFM at NLO for different PDF sets, used. The relative uncertainty due to PDF and scale variations are indicated. |

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Table 6:
The partial $\chi ^2$ per number of data points, $n_{\text{dp}}$, and the global $\chi ^2$ per number of degree of freedom, $n_{\text{dof}}$, resulting from the PDF fit. |

Summary |

The associated production of W bosons with charm quarks in pp collisions at ${\sqrt{s}}$ = 13 TeV is measured using the data collected by the CMS experiment in 2016 and corresponding to an integrated luminosity of $\mathcal{L}_{int}$ = 35.7 fb$^{-1}$. The W boson is detected through the presence of a high-$p_{\mathrm{T}}$ muon and missing transverse momentum. The charm quark is identified through the full reconstruction of ${{\mathrm{D}^{*}(2010)^{\pm}}}$ mesons, in decays ${{\mathrm{D}^{*}(2010)^{\pm}}} \to {\mathrm{D^0}} + \pi^{\pm}_{\text{slow}} \to \mathrm{K}^{\mp} + \pi^{\pm} + \pi^{\pm}_{\text{slow}}$. Since W+c is produced with the W boson and the charm quark of opposite charges, contributions from background processes, mainly c quark production from gluon splitting, are largely removed by subtracting the events in which the charges of the W boson and of the ${{\mathrm{D}^{*}(2010)^{\pm}}}$ meson have the same sign. The cross sections are measured in the kinematic range $|p_{\mathrm{T}}^{\mu}| > $ 26 GeV, $|\eta^{\mu}| < $ 2.4 and $p_{\mathrm{T}}^{\mathrm{c}} > $ 5 GeV, inclusively and in five bins of the absolute pseudorapidity of the muon coming from the W boson decay. The values for the inclusive cross section and for the cross section ratio are obtained as |

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Compact Muon Solenoid LHC, CERN |