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| CMS-SMP-19-011 ; CERN-EP-2020-206 | ||
| Measurement of differential cross sections for Z bosons produced in association with charm jets in pp collisions at $\sqrt{s} = $ 13 TeV | ||
| CMS Collaboration | ||
| 7 December 2020 | ||
| JHEP 04 (2021) 109 | ||
| Abstract: Measurements are presented of differential cross sections for the production of Z bosons in association with at least one jet initiated by a charm quark in pp collisions at $\sqrt{s} = $ 13 TeV. The data recorded by the CMS experiment at the LHC correspond to an integrated luminosity of 35.9 fb$^{-1}$. The final states that contain a pair of electrons or muons that are the decay products of a Z boson, and a jet consistent with being initiated by a charm quark produced in the hard interaction. Differential cross sections as a function of the ${p_{\mathrm{T}}}$ of the Z boson and ${p_{\mathrm{T}}}$ of the charm jet are compared with predictions from Monte Carlo event generators. The inclusive production cross section 405.4 $\pm$ 5.6 (stat) $\pm$ 24.3 (exp) $\pm$ 3.7 (theo) pb, is measured in a fiducial region requiring both leptons to have $| \eta | < $ 2.4 and ${p_{\mathrm{T}}} > $ 10 GeV, at least one lepton with ${p_{\mathrm{T}}} > $ 26 GeV, and a mass of the pair in the range 71-111 GeV, while the charm jet is required to have ${p_{\mathrm{T}}} > $ 30 GeV and $| \eta | < $ 2.4. These are the first measurements of these cross sections in proton-proton collisions at 13 TeV. | ||
| Links: e-print arXiv:2012.04119 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Example Feynman diagram for the Z$+$c-jet process. |
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Figure 2:
Distribution of the secondary vertex mass ${M_{\mathrm {SV}}}$ of the highest-${{p_{\mathrm {T}}}}$ c-tagged central jet, for electron (left) and muon (right) channels.The observed data is compared with the different signal and background components in simulation, before normalization scale factors are applied. Dashed area represents MC systematic uncertainties. The vertical bars on the data points represent statistical uncertainties. |
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Figure 2-a:
Distribution of the secondary vertex mass ${M_{\mathrm {SV}}}$ of the highest-${{p_{\mathrm {T}}}}$ c-tagged central jet, for the electron channel.The observed data is compared with the different signal and background components in simulation, before normalization scale factors are applied. Dashed area represents MC systematic uncertainties. The vertical bars on the data points represent statistical uncertainties. |
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Figure 2-b:
Distribution of the secondary vertex mass ${M_{\mathrm {SV}}}$ of the highest-${{p_{\mathrm {T}}}}$ c-tagged central jet, for the electron channel.The observed data is compared with the different signal and background components in simulation, before normalization scale factors are applied. Dashed area represents MC systematic uncertainties. The vertical bars on the data points represent statistical uncertainties. |
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Figure 3:
Distribution of the secondary vertex mass of the highest-${{p_{\mathrm {T}}}}$ c-tagged central jet, for electron (left) and muon (right) channels for Z$+$light-jet, Z$+$c-jet and Z$+$b-jet components, normalized to 1. Vertical bars represent statistical uncertainties. |
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Figure 3-a:
Distribution of the secondary vertex mass of the highest-${{p_{\mathrm {T}}}}$ c-tagged central jet, for the electron channel for Z$+$light-jet, Z$+$c-jet and Z$+$b-jet components, normalized to 1. Vertical bars represent statistical uncertainties. |
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Figure 3-b:
Distribution of the secondary vertex mass of the highest-${{p_{\mathrm {T}}}}$ c-tagged central jet, for the muon channel for Z$+$light-jet, Z$+$c-jet and Z$+$b-jet components, normalized to 1. Vertical bars represent statistical uncertainties. |
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Figure 4:
The distributions of ${p_{\mathrm {T}}}$ in data and corrected simulation, after applying the fitted scale factors to the Drell-Yan components. The upper plots show distributions for the electron channel, with the ${p_{\mathrm {T}}}$ of the electron pair (left) and c-tagged jet (right). The lower plots show distributions for the muon channel with the ${p_{\mathrm {T}}}$ of the muon pair (left) and c-tagged jet (right). Dashed area represents MC systematic uncertainties. The vertical bars on the data points represent statistical uncertainties. |
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Figure 4-a:
The distribution of the ${p_{\mathrm {T}}}$ of the electron pair in data and corrected simulation, after applying the fitted scale factors to the Drell-Yan components, for the electron channel. Dashed area represents MC systematic uncertainties. The vertical bars on the data points represent statistical uncertainties. |
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Figure 4-b:
The distribution of the ${p_{\mathrm {T}}}$ of the c-tagged jet in data and corrected simulation, after applying the fitted scale factors to the Drell-Yan components, for the electron channel. Dashed area represents MC systematic uncertainties. The vertical bars on the data points represent statistical uncertainties. |
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Figure 4-c:
The distribution of the ${p_{\mathrm {T}}}$ of the muon pair in data and corrected simulation, after applying the fitted scale factors to the Drell-Yan components, for the muon channel. Dashed area represents MC systematic uncertainties. The vertical bars on the data points represent statistical uncertainties. |
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Figure 4-d:
The distribution of the ${p_{\mathrm {T}}}$ of the c-tagged jet in data and corrected simulation, after applying the fitted scale factors to the Drell-Yan components, for the muon channel. Dashed area represents MC systematic uncertainties. The vertical bars on the data points represent statistical uncertainties. |
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Figure 5:
Fraction of selected Z$+$c-jet events originating within the fiducial phase space as a function of ${p_{\mathrm {T}}}$. The plots show distributions for electron and muons channels as a function of ${{p_{\mathrm {T}}} ^{\mathrm{Z}}}$ (left) and ${{p_{\mathrm {T}}} ^{{\mathrm{c}}\text {-tagged jet}}}$ (right). |
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Figure 5-a:
Fraction of selected Z$+$c-jet events originating within the fiducial phase space as a function of ${p_{\mathrm {T}}}$. The plot shows the distribution for electron and muons channels as a function of ${{p_{\mathrm {T}}} ^{\mathrm{Z}}}$. |
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Figure 5-b:
Fraction of selected Z$+$c-jet events originating within the fiducial phase space as a function of ${p_{\mathrm {T}}}$. The plot shows the distribution for electron and muons channels as a function of ${{p_{\mathrm {T}}} ^{{\mathrm{c}}\text {-tagged jet}}}$ . |
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Figure 6:
Efficiency as a function of ${p_{\mathrm {T}}}$. The plots show distributions for the electron and muon channels, as a function of ${{p_{\mathrm {T}}} ^{\mathrm{Z}}}$ (left) and ${{p_{\mathrm {T}}} ^{\mathrm{c} \text {jet}}}$ (right). |
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Figure 6-a:
Efficiency as a function of ${p_{\mathrm {T}}}$. The plot shows the distribution for the electron and muon channels, as a function of ${{p_{\mathrm {T}}} ^{\mathrm{Z}}}$. |
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Figure 6-b:
Efficiency as a function of ${p_{\mathrm {T}}}$. The plot shows the distribution for the electron and muon channels, as a function of ${{p_{\mathrm {T}}} ^{\mathrm{c} \text {jet}}}$. |
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Figure 7:
Measured fiducial differential cross sections for inclusive Z$+$c-jet production, ${{\mathrm {d}}\sigma /{{\mathrm {d}} {{p_{\mathrm {T}}} ^{\mathrm{c} \text {jet}}}}}$ (left) and ${{\mathrm {d}}\sigma /{{\mathrm {d}} {{p_{\mathrm {T}}} ^{\mathrm{Z}}}}}$ (right). Yellow band shows total systematic uncertainties. Predictions from MG5_aMC (LO) are shown with statistical uncertainties only. The vertical bars on the data points represent statistical uncertainties. |
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Figure 7-a:
Measured fiducial differential cross sections for inclusive Z$+$c-jet production, ${{\mathrm {d}}\sigma /{{\mathrm {d}} {{p_{\mathrm {T}}} ^{\mathrm{c} \text {jet}}}}}$. ${{\mathrm {d}}\sigma /{{\mathrm {d}} {{p_{\mathrm {T}}} ^{\mathrm{Z}}}}}$. Yellow band shows total systematic uncertainties. Predictions from MG5_aMC (LO) are shown with statistical uncertainties only. The vertical bars on the data points represent statistical uncertainties. |
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Figure 7-b:
Measured fiducial differential cross sections for inclusive Z$+$c-jet production, ${{\mathrm {d}}\sigma /{{\mathrm {d}} {{p_{\mathrm {T}}} ^{\mathrm{c} \text {jet}}}}}$ (left) and ${{\mathrm {d}}\sigma /{{\mathrm {d}} {{p_{\mathrm {T}}} ^{\mathrm{Z}}}}}$ (right). Yellow band shows total systematic uncertainties. Predictions from MG5_aMC (LO) are shown with statistical uncertainties only. The vertical bars on the data points represent statistical uncertainties. |
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Figure A1:
Distribution of the secondary vertex mass of the highest-${{p_{\mathrm {T}}}}$ c-tagged central jet, for electron channel.The observed data is compared to the different signal and background components in simulation, after normalization scale factors as function of Z ${p_{\mathrm {T}}}$ (left) and c-tagged central jet ${p_{\mathrm {T}}}$ (right) are applied. |
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Figure A1-a:
Distribution of the secondary vertex mass of the highest-${{p_{\mathrm {T}}}}$ c-tagged central jet, for electron channel.The observed data is compared to the different signal and background components in simulation, after normalization scale factors as function of Z ${p_{\mathrm {T}}}$ are applied. |
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Figure A1-b:
Distribution of the secondary vertex mass of the highest-${{p_{\mathrm {T}}}}$ c-tagged central jet, for electron channel.The observed data is compared to the different signal and background components in simulation, after normalization scale factors as function of c-tagged central jet ${p_{\mathrm {T}}}$ are applied. |
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Figure A2:
Distribution of the secondary vertex mass of the highest-${{p_{\mathrm {T}}}}$ c-tagged central jet, for muon channel.The observed data is compared to the different signal and background components in simulation, after normalization scale factors as function of Z ${p_{\mathrm {T}}}$ (left) and c-tagged central jet ${p_{\mathrm {T}}}$ (right) are applied. |
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Figure A2-a:
Distribution of the secondary vertex mass of the highest-${{p_{\mathrm {T}}}}$ c-tagged central jet, for muon channel.The observed data is compared to the different signal and background components in simulation, after normalization scale factors as function of Z ${p_{\mathrm {T}}}$ are applied. |
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Figure A2-b:
Distribution of the secondary vertex mass of the highest-${{p_{\mathrm {T}}}}$ c-tagged central jet, for muon channel.The observed data is compared to the different signal and background components in simulation, after normalization scale factors as function of c-tagged central jet ${p_{\mathrm {T}}}$ are applied. |
| Tables | |
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Table 1:
Values of Z$+$light-jet ${SF_\mathrm {l}}$, Z$+$c-jet ${SF_\mathrm{c}}$, and Z$+$b-jet ${SF_\mathrm{b}}$ scale factors measured in the electron channel, as a function of c-tagged jet ${p_{\mathrm {T}}}$. The first uncertainty in each case is the statistical uncertainty from the fit, the second is the systematic uncertainty. |
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Table 2:
Values of Z$+$light-jet ${SF_\mathrm {l}}$, Z$+$c-jet ${SF_\mathrm{c}}$, and Z$+$b-jet ${SF_\mathrm{b}}$ scale factors measured in the electron channel, as a function of Z candidate ${p_{\mathrm {T}}}$. The first uncertainty in each case is the statistical uncertainty from the fit, the second is the systematic uncertainty. |
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Table 3:
Values of Z$+$light-jet ${SF_\mathrm {l}}$, Z$+$c-jet ${SF_\mathrm{c}}$, and Z$+$b-jet ${SF_\mathrm{b}}$ scale factors measured in the muon channel, as a function of c-tagged jet ${p_{\mathrm {T}}}$. The first uncertainty in each case is the statistical uncertainty from the fit, the second is the systematic uncertainty. |
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Table 4:
Values of Z$+$light-jet ${SF_\mathrm {l}}$, Z$+$c-jet ${SF_\mathrm{c}}$, and Z$+$b-jet ${SF_\mathrm{b}}$ scale factors measured in the muon channel, as a function of Z candidate ${p_{\mathrm {T}}}$. The first uncertainty in each case is the statistical uncertainty from the fit, the second is the systematic uncertainty. |
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Table 5:
Summary of the systematic uncertainties in the integral fiducial cross section arising from the various sources. |
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Table 6:
Measured differential cross section as a function of ${{p_{\mathrm {T}}} ^{\mathrm{c} \text {jet}}}$ for electron, muon and combine channels. The first and second uncertainty values correspond to the statistical and systematic contributions, respectively. |
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Table 7:
Measured differential cross section as a function of ${{p_{\mathrm {T}}} ^{\mathrm{Z}}}$ for electron, muon and combine channels. The first and second uncertainty values correspond to the statistical and systematic contributions, respectively. |
| Summary |
|
The first differential cross sections for inclusive Z$+$c-jet production as functions of transverse momenta ${p_{\mathrm{T}}}$ of the Z boson and of the associated c-jet are presented for collisions at $\sqrt{s} = $ 13 TeV using 35.9 fb$^{-1}$ of data collected by the CMS experiment at the CERN LHC. The measurements pertain to a fiducial space defined as containing a c-jet with $ {p_{\mathrm{T}}} > $ 30 GeV and pseudorapidity $| \eta | < $ 2.4, and a pair of leptons with each lepton having ${p_{\mathrm{T}}} > $ 10 GeV, $| \eta | < $ 2.4, and at least one with ${p_{\mathrm{T}}} > $ 26 GeV, and a dilepton mass between 71 and 111 GeV. The main backgrounds correspond to Z$+$light-jet, Z$+$b-jet, top quark pair, and diboson (ZZ, ZW, or WW) production. To provide a direct comparison with predictions from Monte Carlo (MC) event generators, we unfold detector effects from our measurements. The total fiducial cross section for the Z boson with ${p_{\mathrm{T}}} < $ 300 GeV is measured to be 405.4 $\pm$ 5.6 (stat) $\pm$ 24.3 (exp) $\pm$ 3.7 (theo) pb, while the MadGraph5+MCatNLO generator at next-to-leading order predicts 524.9 $\pm$ 11.7 (theo) pb for the same fiducial region. The theoretical uncertainties include QCD scale variation and parton distribution function uncertainties. The predictions from MC event generators were compared with measurements, which are in good agreement with MadGraph5+MCatNLO at leading order, while both MadGraph5+MCatNLO and SHERPA at next-to-leading order tend to overestimate the cross section. Predictions from all three generators were normalized to the cross section calculated with FEWZ at next-to-next-to-leading order. Since the prediction of inclusive Z$+$jets production at next-to-leading order is in better agreement with data than that at leading order [45]. This could be an indication that the parton distribution functions overestimate the charm content. These results can be used to improve existing constraints on the charm quark content in the proton. |
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