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| CMS-PAS-SMP-19-004 | ||
| 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 | ||
| August 2019 | ||
| Abstract: Ratios of cross sections, $\sigma$(Z + c jets)/$\sigma$(Z + jets), $\sigma$(Z + b jets)/$\sigma$(Z + jets), and $\sigma$(Z + c jets)/$\sigma$(Z + b jets) in the associated production of a Z boson with at least one charm or bottom quark jet are measured in pp collisions at $\sqrt{s}= $ 13 TeV using 35.9 fb$^{-1}$ of data collected by the CMS experiment at the CERN LHC. The fiducial volume of the measurement is defined by jet transverse momentum $p_{\mathrm{T}} > $ 30 GeV and pseudorapidity $|{\eta}| < $ 2.4. 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. 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 QCD calculations. These are the first of a kind measurements at 13 TeV, and the measurement precision exceeds that of the current theoretical predictions. | ||
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Links:
CDS record (PDF) ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, PRD 102 (2020) 032007. The superseded preliminary plots can be found here. |
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| Figures | |
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Figure 1:
Comparison of c jet (left), b jet (right) M$_{\text {SV}}$ in data and MC simulation. The correction to account for the difference between the b jets in ${\mathrm{t} {}\mathrm{\bar{t}}}$ and Z + b jets processes is applied to the data distribution in the right panel. |
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Figure 1-a:
Comparison of c jet (left), b jet (right) M$_{\text {SV}}$ in data and MC simulation. The correction to account for the difference between the b jets in ${\mathrm{t} {}\mathrm{\bar{t}}}$ and Z + b jets processes is applied to the data distribution in the right panel. |
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Figure 1-b:
Comparison of c jet (left), b jet (right) M$_{\text {SV}}$ in data and MC simulation. The correction to account for the difference between the b jets in ${\mathrm{t} {}\mathrm{\bar{t}}}$ and Z + b jets processes is applied to the data distribution in the right panel. |
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Figure 2:
Post-fit M$_{\text {SV}}$ distributions for electron (left) and muon (right) channels in the inclusive measurement. |
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Figure 2-a:
Post-fit M$_{\text {SV}}$ distributions for electron (left) and muon (right) channels in the inclusive measurement. |
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Figure 2-b:
Post-fit M$_{\text {SV}}$ distributions for electron (left) and muon (right) channels in the inclusive measurement. |
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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 QCD scales (renormalization and factorization) 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 QCD scales (renormalization and factorization) 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 QCD scales (renormalization and factorization) 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 predictions are slightly shifted along the x-axis in the upper plots and their total PDF and QCD scales (renormalization and factorization) 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 predictions are slightly shifted along the x-axis in the upper plots and their total PDF and QCD scales (renormalization and factorization) 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 predictions are slightly shifted along the x-axis in the upper plots and their total PDF and QCD scales (renormalization and factorization) 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 in data are statistical while the hatched band represents the total uncertainties. The predictions are slightly shifted along the x-axis to ease readability in the upper plots and their total PDF and QCD scales (renormalization and factorization) uncertainties are shown as error bands in the ratio plots. |
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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 in data are statistical while the hatched band represents the total uncertainties. The predictions are slightly shifted along the x-axis to ease readability in the upper plots and their total PDF and QCD scales (renormalization and factorization) uncertainties are shown as error bands in the ratio plots. |
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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 in data are statistical while the hatched band represents the total uncertainties. The predictions are slightly shifted along the x-axis to ease readability in the upper plots and their total PDF and QCD scales (renormalization and factorization) uncertainties are shown as error bands in the ratio plots. |
| Tables | |
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Table 1:
Numbers of events after the Z + jets selection in the electron and muon channels. The uncertainties are statistical only. |
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Table 2:
Numbers of events after the Z + HF jets selection in the electron and muon channels. The uncertainties are statistical only. |
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Table 3:
The SF$_\text {c}$, SF$_\text {b}$ 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 fraction of the observed number of Z + c jets and Z + b jets in the total Z + jets events are shown in the parentheses and are derived by applying the scale factors to the corresponding MC events. |
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Table 4:
The SF$_\text {c}$, SF$_\text {b}$ 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 Z + c jets and Z + b jets in the total Z + jets events with the total uncertainty are shown in the parentheses and are derived by applying the scale factors to the corresponding MC events. |
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Table 5:
Systematic uncertainties in the scale factor measurements. The indicated ranges correspond to the various jet and Z ${p_{\mathrm {T}}}$ bins. |
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Table 6:
The systematic uncertainties in the cross section ratio measurements. The indicated ranges correspond to the various jet and Z ${p_{\mathrm {T}}}$ bins. |
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Table 7:
The 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 8:
The 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 9:
The predicted cross section ratios from NLO and LO MG5_aMC. The first and second sets of uncertainties correspond to PDF and QCD scales (renormalization and factorization) variations, respectively. |
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Table 10:
The cross section ratios measured in the electron and muon channels together with the combined results in jet ${p_{\mathrm {T}}}$ bins. |
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Table 11:
The cross section ratios measured in the electron and muon channels together with the combined results in Z ${p_{\mathrm {T}}}$ bins. |
| Summary |
| Ratios of cross sections, $\sigma$(Z + c jets )/$\sigma$(Z + jets ), $\sigma$(Z + b jets )/$\sigma$(Z + jets ), and $\sigma$(Z + c jets )/$\sigma$(Z + b 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 jet transverse momentum ${p_{\mathrm{T}}} > $ 30 GeV and pseudorapidity $|\eta| < $ 2.4. 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 $\sigma$(Z + c jet )/$\sigma$(Z + jets ) $=$ 0.102 $\pm$ 0.002 $\pm$ 0.009, $\sigma$(Z + b jet )/$\sigma$(Z + jets ) $ =$ 0.0633 $\pm$ 0.0004 $\pm$ 0.0015, and $\sigma$(Z + c jet )/$\sigma$(Z + b jet ) $=$ 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 to predictions from leading and next-to-leading order perturbative QCD calculations. These are the first of a kind measurements at 13 TeV, and the measurement precision exceeds that of the current theoretical predictions. |
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