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| CMS-SMP-19-004 ; CERN-EP-2019-262 | ||
| Measurement of the associated production of a Z boson with charm or bottom quark jets in proton-proton collisions at $\sqrt{s}=$ 13 TeV | ||
| CMS Collaboration | ||
| 19 January 2020 | ||
| Phys. Rev. D 102 (2020) 032007 | ||
| Abstract: Ratios of cross sections, $\sigma(\mathrm{Z+c\ \text{jets}})/\sigma(\mathrm{Z+ \text{jets}})$, $\sigma(\mathrm{Z+b\ \text{jets}})/\sigma(\mathrm{Z+ \text{jets}})$, and $\sigma(\mathrm{Z+c\ \text{jets}})/\sigma(\mathrm{Z+b\ \text{jets}})$ in the associated production of a Z boson with at least one charm or bottom quark jet are measured in proton-proton collisions at $\sqrt{s}=$ 13 TeV. The data sample, collected by the CMS experiment at the CERN LHC, corresponds to an integrated luminosity of 35.9 fb$^{-1}$, with a fiducial volume of ${p_{\mathrm{T}}} > $ 30 GeV and $|\eta| < $ 2.4 for the jets, where ${p_{\mathrm{T}}}$ and $\eta$ represent transverse momentum and pseudorapidity, respectively. The Z boson candidates come from leptonic decays into electrons or muons with ${p_{\mathrm{T}}} > $ 25 GeV and $|{\eta}| < $ 2.4, and the dilepton mass satisfies 71 $ < m_{\mathrm{Z}} < $ 111 GeV. The measured values are $\sigma(\mathrm{Z+c\ \text{jets}})/\sigma(\mathrm{Z+ \text{jets}}) = $ 0.102 $\pm$ 0.002 $\pm$ 0.009, $\sigma(\mathrm{Z+b\ \text{jets}})/\sigma(\mathrm{Z+ \text{jets}}) = $ 0.0633 $\pm$ 0.0004 $\pm$ 0.0015, and $\sigma(\mathrm{Z+c\ \text{jets}})/\sigma(\mathrm{Z+b\ \text{jets}}) = $ 1.62 $\pm$ 0.03 $\pm$ 0.15. Results on the inclusive and differential cross section ratios as functions of jet and Z boson transverse momentum are compared with predictions from leading and next-to-leading order perturbative quantum chromodynamics calculations. These are the first measurements of the cross section ratios at 13 TeV, and the measurement precision is better than that of the current theoretical predictions. | ||
| Links: e-print arXiv:2001.06899 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Comparisons of c jet (left) and b jet (right) ${M_\ \text {SV}}$ distributions for data and simulation. A shape correction is applied to the data-driven distribution in the right panel to account for the difference between the jets in ${\mathrm{t} {}\mathrm{\bar{t}}}$ and $\mathrm{Z+b \ \text{jets}}$ processes. |
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Figure 1-a:
Comparisons of c jet (left) and b jet (right) ${M_\ \text {SV}}$ distributions for data and simulation. A shape correction is applied to the data-driven distribution in the right panel to account for the difference between the jets in ${\mathrm{t} {}\mathrm{\bar{t}}}$ and $\mathrm{Z+b \ \text{jets}}$ processes. |
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Figure 1-b:
Comparisons of c jet (left) and b jet (right) ${M_\ \text {SV}}$ distributions for data and simulation. A shape correction is applied to the data-driven distribution in the right panel to account for the difference between the jets in ${\mathrm{t} {}\mathrm{\bar{t}}}$ and $\mathrm{Z+b \ \text{jets}}$ processes. |
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Figure 2:
Secondary vertex invariant mass distributions for the electron (left) and muon (right) channels derived from fits using the inclusive $\mathrm{Z+\ \text{HF jets}}$ data sample. The post-fit uncertainty bands indicate the total uncertainties, added in quadrature, of the best-fit values of signal and background process rates. |
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Figure 2-a:
Secondary vertex invariant mass distributions for the electron (left) and muon (right) channels derived from fits using the inclusive $\mathrm{Z+\ \text{HF jets}}$ data sample. The post-fit uncertainty bands indicate the total uncertainties, added in quadrature, of the best-fit values of signal and background process rates. |
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Figure 2-b:
Secondary vertex invariant mass distributions for the electron (left) and muon (right) channels derived from fits using the inclusive $\mathrm{Z+\ \text{HF jets}}$ data sample. The post-fit uncertainty bands indicate the total uncertainties, added in quadrature, of the best-fit values of signal and background process rates. |
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Figure 3:
Unfolded, particle-level mg5\_aMC, and parton-level mcfm R(c/j) cross section ratios versus jet (left) and Z boson (right) transverse momentum. The vertical error bars for the data points are statistical while the hatched band represents the total uncertainties. The predictions are slightly shifted along the $x$-axis for readability in the upper plots, and their total PDF and scale uncertainties are shown as error bands in the ratio plots. |
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Figure 3-a:
Unfolded, particle-level mg5\_aMC, and parton-level mcfm R(c/j) cross section ratios versus jet (left) and Z boson (right) transverse momentum. The vertical error bars for the data points are statistical while the hatched band represents the total uncertainties. The predictions are slightly shifted along the $x$-axis for readability in the upper plots, and their total PDF and scale uncertainties are shown as error bands in the ratio plots. |
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Figure 3-b:
Unfolded, particle-level mg5\_aMC, and parton-level mcfm R(c/j) cross section ratios versus jet (left) and Z boson (right) transverse momentum. The vertical error bars for the data points are statistical while the hatched band represents the total uncertainties. The predictions are slightly shifted along the $x$-axis for readability in the upper plots, and their total PDF and scale uncertainties are shown as error bands in the ratio plots. |
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Figure 4:
Unfolded, particle-level mg5\_aMC, and parton-level mcfm R(b/j) cross section ratio versus jet (left) and Z boson (right) transverse momentum. The vertical error bars for the data points are statistical while the hatched band presents the total uncertainties. The predictions are slightly shifted along the $x$-axis for readability in the upper plots, and their total PDF and scale uncertainties are shown as error bands in the ratio plots. |
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Figure 4-a:
Unfolded, particle-level mg5\_aMC, and parton-level mcfm R(b/j) cross section ratio versus jet (left) and Z boson (right) transverse momentum. The vertical error bars for the data points are statistical while the hatched band presents the total uncertainties. The predictions are slightly shifted along the $x$-axis for readability in the upper plots, and their total PDF and scale uncertainties are shown as error bands in the ratio plots. |
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Figure 4-b:
Unfolded, particle-level mg5\_aMC, and parton-level mcfm R(b/j) cross section ratio versus jet (left) and Z boson (right) transverse momentum. The vertical error bars for the data points are statistical while the hatched band presents the total uncertainties. The predictions are slightly shifted along the $x$-axis for readability in the upper plots, and their total PDF and scale uncertainties are shown as error bands in the ratio plots. |
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Figure 5:
Unfolded, particle-level mg5\_aMC, and parton-level mcfm R(c/b) cross section ratio versus jet (left) and Z boson (right) transverse momentum. The vertical error bars for the data points are statistical while the hatched band represents the total uncertainties. The predictions are slightly shifted along the $x$-axis for readability in the upper plots, and their total PDF and scale uncertainties are shown as error bands in the ratio plots. |
png pdf |
Figure 5-a:
Unfolded, particle-level mg5\_aMC, and parton-level mcfm R(c/b) cross section ratio versus jet (left) and Z boson (right) transverse momentum. The vertical error bars for the data points are statistical while the hatched band represents the total uncertainties. The predictions are slightly shifted along the $x$-axis for readability in the upper plots, and their total PDF and scale uncertainties are shown as error bands in the ratio plots. |
png pdf |
Figure 5-b:
Unfolded, particle-level mg5\_aMC, and parton-level mcfm R(c/b) cross section ratio versus jet (left) and Z boson (right) transverse momentum. The vertical error bars for the data points are statistical while the hatched band represents the total uncertainties. The predictions are slightly shifted along the $x$-axis for readability in the upper plots, and their total PDF and scale uncertainties are shown as error bands in the ratio plots. |
| Tables | |
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Table 1:
Numbers of events that satisfy the $\mathrm{Z+ \text{jets}}$ and $\mathrm{Z+\ \text{HF jets}}$ selection criteria in the electron and muon channels. The uncertainties are statistical only. |
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Table 2:
The ${\mathrm {SF}_{\mathrm{c}}}$ and ${\mathrm {SF}_{\mathrm{b}}}$ scale factor fit results for electron, muon, and combined channels in jet ${p_{\mathrm {T}}}$ bins. The first and second uncertainty values correspond to the statistical and systematic contributions, respectively. The fractions of the observed number of $\mathrm{Z+c \ \text{jets}}$ and $\mathrm{Z+b \ \text{jets}}$ in the total number of $\mathrm{Z+ \text{jets}}$ events selected in the $\mathrm{Z+\ \text{HF jets}}$ sample are shown in the parentheses and are determined by applying the scale factors to the corresponding MC events. |
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Table 3:
The ${\mathrm {SF}_{\mathrm{c}}}$ and ${\mathrm {SF}_{\mathrm{b}}}$ scale factor fit results for electron, muon, and combined channels in Z ${p_{\mathrm {T}}}$ bins. The first and second uncertainty values correspond to the statistical and systematic contributions, respectively. The fraction of the observed number of $\mathrm{Z+c \ \text{jets}}$ and $\mathrm{Z+b \ \text{jets}}$ in the total number of $\mathrm{Z+ \text{jets}}$ events selected in the $\mathrm{Z+\ \text{HF jets}}$ sample are shown in the parentheses and are derived by applying the scale factors to the corresponding MC events. |
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Table 4:
Systematic uncertainties in the scale factor measurements. The uncertainty ranges correspond to variations across jet and Z ${p_{\mathrm {T}}}$ bins. |
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Table 5:
The systematic uncertainties in the cross section ratio measurements. The uncertainty ranges correspond to variations across jet and Z ${p_{\mathrm {T}}}$ bins. |
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Table 6:
Cross section ratios measured in the electron and muon channels, along with the combined results. The first and second uncertainty values correspond to the statistical and systematic contributions, respectively. |
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Table 7:
Unfolded cross section ratios in the electron and muon channels, along with the combined results. The first and second uncertainty values correspond to the statistical and systematic contributions, respectively. |
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Table 8:
Predicted cross section ratios from mg5\_aMC and mcfm at LO and NLO accuracy. The first and second sets of uncertainties correspond to PDF and scale variations, respectively. |
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Table 9:
The cross section ratios for the electron, muon, and combined channels in jet ${p_{\mathrm {T}}}$ bins. |
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Table 10:
The cross section ratios in the electron, muon and combined channels in the Z boson ${p_{\mathrm {T}}}$ bins. |
| Summary |
| Ratios of cross sections, $\sigma(\mathrm{Z+c\ \text{jets}})/\sigma(\mathrm{Z+ \text{jets}})$, $\sigma(\mathrm{Z+b\ \text{jets}})/\sigma(\mathrm{Z+ \text{jets}})$, and $\sigma(\mathrm{Z+c\ \text{jets}})/\sigma(\mathrm{Z+b\ \text{jets}})$ in the associated production of a Z boson with at least one charm or bottom quark jet have been measured in proton-proton collisions at $\sqrt{s} = $ 13 TeV using 35.9 fb$^{-1}$ of data collected by the CMS experiment at the LHC. The fiducial volume of the measurement is defined by ${p_{\mathrm{T}}} > $ 30 GeV and $|\eta| < $ 2.4 for the jets, where ${p_{\mathrm{T}}}$ and $\eta$ represent transverse momentum and pseudorapidity, respectively. The Z bosons are selected within the mass range of 71 and 111 GeV requiring leptons (electrons or muons) with ${p_{\mathrm{T}}} > $ 25 GeV and $|{\eta}| < $ 2.4. The measured values are $\sigma(\mathrm{Z+c\ \text{jets}})/\sigma(\mathrm{Z+ \text{jets}}) = $ 0.102 $\pm$ 0.002 $\pm$ 0.009, $\sigma(\mathrm{Z+b\ \text{jets}})/\sigma(\mathrm{Z+ \text{jets}}) = $ 0.0633 $\pm$ 0.0004 $\pm$ 0.0015, and $\sigma(\mathrm{Z+c\ \text{jets}})/\sigma(\mathrm{Z+b\ \text{jets}}) = $ 1.62 $\pm$ 0.03 $\pm$ 0.15. Results for the inclusive and differential cross section ratios as functions of jet and Z boson transverse momentum are compared with predictions from leading and next-to-leading order perturbative quantum chromodynamics calculations. These are the first results of this kind at 13 TeV, and the measurement precision exceeds that of the current theoretical predictions. |
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