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| CMS-PAS-SMP-20-015 | ||
| Measurement of Z+b jets cross section in proton-proton collisions at $\sqrt{s}= $ 13 TeV | ||
| CMS Collaboration | ||
| July 2021 | ||
| Abstract: The measurements of the cross section of the Z boson, decaying to dielectrons or dimuons, in association with at least one bottom quark jet are performed with proton-proton collision data at $\sqrt{s}= $ 13 TeV. The data sample corresponds to an integrated luminosity of 137.1 fb$^{-1}$, collected by the CMS experiment at the LHC. The integrated cross sections of Z $+ \geq$ 1 b jet and Z $+ \geq$ 2 b jets are reported for the electron, muon, and combined channels with full Run 2 data. The measured integrated cross sections are 6.52 $\pm$ 0.04 (stat) $\pm$ 0.40 (syst) $\pm$ 0.14 (theo) pb for Z $+ \geq$ 1 b jet and 0.65 $\pm$ 0.03 (stat) $\pm$ 0.07 (syst) $\pm$ 0.02 (theo) pb for Z $+ \geq$ 2 b jets. The differential cross section distributions are measured as a function of various kinematic observables that are useful for precision tests of the perturbative quantum chromodynamics predictions. The ratios of integrated and differential cross sections of Z $+ \geq$ 2 b jets and Z $+ \geq$ 1 b jet processes are also determined. The value of the integrated cross section ratio measured in the combined channel is 0.100 $\pm$ 0.005 (stat) $\pm$ 0.007 (syst) $\pm$ 0.003 (theo). All of the measurements are compared with predictions from Monte Carlo simulations. | ||
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These preliminary results are superseded in this paper, PRD 105 (2022) 092014. The superseded preliminary plots can be found here. |
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| Figures | |
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Figure 1:
Examples of Feynman diagrams for Z $+$ 1 b jet (left) and Z $+$ 2 b jets (middle and right). |
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Figure 1-a:
Examples of Feynman diagrams for Z $+$ 1 b jet (left) and Z $+$ 2 b jets (middle and right). |
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Figure 1-b:
Examples of Feynman diagrams for Z $+$ 1 b jet (left) and Z $+$ 2 b jets (middle and right). |
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Figure 1-c:
Examples of Feynman diagrams for Z $+$ 1 b jet (left) and Z $+$ 2 b jets (middle and right). |
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Figure 2:
(a) Differential cross section and the (b) normalized differential cross section distributions as a function of Z transverse momenta for Z $+ \geq$ 1 b jet events. |
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Figure 2-a:
(a) Differential cross section and the (b) normalized differential cross section distributions as a function of Z transverse momenta for Z $+ \geq$ 1 b jet events. |
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Figure 2-b:
(a) Differential cross section and the (b) normalized differential cross section distributions as a function of Z transverse momenta for Z $+ \geq$ 1 b jet events. |
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Figure 3:
(a) Differential cross section and the (b) normalized differential cross section distributions as a function of b jet transverse momenta for Z $+ \geq$ 1 b jet events. |
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Figure 3-a:
(a) Differential cross section and the (b) normalized differential cross section distributions as a function of b jet transverse momenta for Z $+ \geq$ 1 b jet events. |
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Figure 3-b:
(a) Differential cross section and the (b) normalized differential cross section distributions as a function of b jet transverse momenta for Z $+ \geq$ 1 b jet events. |
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Figure 4:
(a) Differential cross section and the (b) normalized differential cross section distributions as a function of b jet absolute pseudorapidity for Z $+ \geq$ 1 b jet events. |
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Figure 4-a:
(a) Differential cross section and the (b) normalized differential cross section distributions as a function of b jet absolute pseudorapidity for Z $+ \geq$ 1 b jet events. |
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Figure 4-b:
(a) Differential cross section and the (b) normalized differential cross section distributions as a function of b jet absolute pseudorapidity for Z $+ \geq$ 1 b jet events. |
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Figure 5:
(a) Differential cross section and the (b) normalized differential cross section distributions as a function of $\Delta \phi ^{(\mathrm{Z},\, \text{ b jet})}$ between Z boson and the leading b jet for Z $+ \geq $ 1 b jet events. |
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Figure 5-a:
(a) Differential cross section and the (b) normalized differential cross section distributions as a function of $\Delta \phi ^{(\mathrm{Z},\, \text{ b jet})}$ between Z boson and the leading b jet for Z $+ \geq $ 1 b jet events. |
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Figure 5-b:
(a) Differential cross section and the (b) normalized differential cross section distributions as a function of $\Delta \phi ^{(\mathrm{Z},\, \text{ b jet})}$ between Z boson and the leading b jet for Z $+ \geq $ 1 b jet events. |
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Figure 6:
(a) Differential cross section and the (b) normalized differential cross section distributions as a function of $\Delta Y^{(\mathrm{Z},\, \text{ b jet})}$ between Z boson and the leading b jet for the Z $+ \geq $ 1 b jet events. |
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Figure 6-a:
(a) Differential cross section and the (b) normalized differential cross section distributions as a function of $\Delta Y^{(\mathrm{Z},\, \text{ b jet})}$ between Z boson and the leading b jet for the Z $+ \geq $ 1 b jet events. |
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Figure 6-b:
(a) Differential cross section and the (b) normalized differential cross section distributions as a function of $\Delta Y^{(\mathrm{Z},\, \text{ b jet})}$ between Z boson and the leading b jet for the Z $+ \geq $ 1 b jet events. |
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Figure 7:
(a) Differential cross section and the (b) normalized differential cross section distributions as a function of $\Delta R^{(\mathrm{Z},\, \text{ b jet})}$ between Z boson and the leading b jet for the Z $+ \geq $ 1 b jet events. |
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Figure 7-a:
(a) Differential cross section and the (b) normalized differential cross section distributions as a function of $\Delta R^{(\mathrm{Z},\, \text{ b jet})}$ between Z boson and the leading b jet for the Z $+ \geq $ 1 b jet events. |
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Figure 7-b:
(a) Differential cross section and the (b) normalized differential cross section distributions as a function of $\Delta R^{(\mathrm{Z},\, \text{ b jet})}$ between Z boson and the leading b jet for the Z $+ \geq $ 1 b jet events. |
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Figure 8:
(a) Differential cross section and the (b) normalized differential cross section distributions as a function of the leading b jet transverse momentum for the Z $+ \geq $ 2 b jets events. |
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Figure 8-a:
(a) Differential cross section and the (b) normalized differential cross section distributions as a function of the leading b jet transverse momentum for the Z $+ \geq $ 2 b jets events. |
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Figure 8-b:
(a) Differential cross section and the (b) normalized differential cross section distributions as a function of the leading b jet transverse momentum for the Z $+ \geq $ 2 b jets events. |
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Figure 9:
(a) Differential and the (b) normalized differential cross section distributions as a function of the leading b jet absolute pseudorapidity for the Z $+ \geq $ 2 b jets events. |
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Figure 9-a:
(a) Differential and the (b) normalized differential cross section distributions as a function of the leading b jet absolute pseudorapidity for the Z $+ \geq $ 2 b jets events. |
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Figure 9-b:
(a) Differential and the (b) normalized differential cross section distributions as a function of the leading b jet absolute pseudorapidity for the Z $+ \geq $ 2 b jets events. |
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Figure 10:
(a) Differential cross section and the (b) normalized differential cross section distributions as a function of the subleading b jet transverse momentum for the Z $+ \geq $ 2 b jets events. |
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Figure 10-a:
(a) Differential cross section and the (b) normalized differential cross section distributions as a function of the subleading b jet transverse momentum for the Z $+ \geq $ 2 b jets events. |
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Figure 10-b:
(a) Differential cross section and the (b) normalized differential cross section distributions as a function of the subleading b jet transverse momentum for the Z $+ \geq $ 2 b jets events. |
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Figure 11:
(a) Differential cross section and the (b) normalized differential cross section distributions as a function of the Z boson transverse momentum. |
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Figure 11-a:
(a) Differential cross section and the (b) normalized differential cross section distributions as a function of the Z boson transverse momentum. |
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Figure 11-b:
(a) Differential cross section and the (b) normalized differential cross section distributions as a function of the Z boson transverse momentum. |
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Figure 12:
(a) Differential cross section and the (b) normalized differential cross section distributions as a function of the angular separation between two b jets, $\Delta R_{\mathrm{bb}}$. |
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Figure 12-a:
(a) Differential cross section and the (b) normalized differential cross section distributions as a function of the angular separation between two b jets, $\Delta R_{\mathrm{bb}}$. |
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Figure 12-b:
(a) Differential cross section and the (b) normalized differential cross section distributions as a function of the angular separation between two b jets, $\Delta R_{\mathrm{bb}}$. |
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Figure 13:
(a) Differential cross section and the (b) normalized differential cross section distributions as a function of the minimum angular separation between the Z boson and two b jets, $\Delta R^{min}_{\mathrm{ Zbb }}$. |
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Figure 13-a:
(a) Differential cross section and the (b) normalized differential cross section distributions as a function of the minimum angular separation between the Z boson and two b jets, $\Delta R^{min}_{\mathrm{ Zbb }}$. |
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Figure 13-b:
(a) Differential cross section and the (b) normalized differential cross section distributions as a function of the minimum angular separation between the Z boson and two b jets, $\Delta R^{min}_{\mathrm{ Zbb }}$. |
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Figure 14:
(a) Differential cross section and the (b) normalized differential cross section distributions as a function of the asymmetry of the Z $+ \geq $ 2 b jets system, $A_{\mathrm{ Zbb }}$. |
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Figure 14-a:
(a) Differential cross section and the (b) normalized differential cross section distributions as a function of the asymmetry of the Z $+ \geq $ 2 b jets system, $A_{\mathrm{ Zbb }}$. |
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Figure 14-b:
(a) Differential cross section and the (b) normalized differential cross section distributions as a function of the asymmetry of the Z $+ \geq $ 2 b jets system, $A_{\mathrm{ Zbb }}$. |
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Figure 15:
(a) Differential cross section and the (b) normalized differential cross section distributions as a function of the invariant mass of two b jets. |
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Figure 15-a:
(a) Differential cross section and the (b) normalized differential cross section distributions as a function of the invariant mass of two b jets. |
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Figure 15-b:
(a) Differential cross section and the (b) normalized differential cross section distributions as a function of the invariant mass of two b jets. |
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Figure 16:
(a) Differential cross section and the (b) normalized differential cross section distributions as a function of the invariant mass of the Z boson and two b jets. |
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Figure 16-a:
(a) Differential cross section and the (b) normalized differential cross section distributions as a function of the invariant mass of the Z boson and two b jets. |
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Figure 16-b:
(a) Differential cross section and the (b) normalized differential cross section distributions as a function of the invariant mass of the Z boson and two b jets. |
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Figure 17:
Distributions of the cross section ratios, $\sigma $(Z $+ \geq $ 2 b jets)/$\sigma $(Z $+ \geq $ 1 b jet), as a function of the (a) leading b jet transverse momentum and (b) absolute pseudorapidity. |
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Figure 17-a:
Distributions of the cross section ratios, $\sigma $(Z $+ \geq $ 2 b jets)/$\sigma $(Z $+ \geq $ 1 b jet), as a function of the (a) leading b jet transverse momentum and (b) absolute pseudorapidity. |
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Figure 17-b:
Distributions of the cross section ratios, $\sigma $(Z $+ \geq $ 2 b jets)/$\sigma $(Z $+ \geq $ 1 b jet), as a function of the (a) leading b jet transverse momentum and (b) absolute pseudorapidity. |
| Tables | |
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Table 1:
Fiducial region definition at particle-level. |
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Table 2:
Summary of uncertainties (in percents) in the integrated cross sections for the dielectron, dimuon, and combined channels in the Z $+ \geq $ 1 b jet and Z $+ \geq $ 2 b jets events. |
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Table 3:
Summary of uncertainties (in percents) in the differential cross section distributions for the combined channel in the Z $+ \geq $ 1 b jet events. |
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Table 4:
Summary of uncertainties (in percents) in the normalized differential distributions for the combined channel in the Z $+ \geq $ 1 b jet events. |
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Table 5:
Summary of uncertainties (in percents) in the differential cross section distributions for the combined channel in the Z $+ \geq $ 2 b jets events. The symbols, b$_1$ and b$_2$, stand for leading and subleading b jets, respectively. |
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Table 6:
Summary of uncertainties (in percents) in the normalized differential distributions for the combined channel in the Z $+ \geq $ 2 b jets events. The symbols, b$_1$ and b$_2$, stand for leading and subleading b jets, respectively. |
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Table 7:
Measured and predicted cross sections (in pb) for the Z $+ \geq $ 1 b jet and Z $+ \geq $ 2 b jets final states. The cross section ratios between the Z $+ \geq $ 2 b jets and Z $+ \geq $ 1 b jet are shown in the last three rows for the dielectron, dimuon, and combined channels. In the measured results the first, second, and third uncertainties correspond to the statistical, systematic, and theoretical sources, respectively. The MG5\_aMC (NLO) predictions include theoretical uncertainties (PDF, renormalization, and factorization scales). |
| Summary |
| A measurement of integrated cross sections of the Z $+ \geq$ 1 b jet and Z $+ \geq$ 2 b jets processes along with the differential and normalized differential cross section distributions of different kinematic observables is performed using proton-proton collision data at $\sqrt s=$ 13 TeV collected by the CMS experiment at the CERN LHC. The integrated cross sections are measured to be 6.52 $\pm$ 0.04 (stat) $\pm$ 0.40 (syst) $\pm$ 0.14 (theo) pb for the Z $+ \geq$ 1 b jet and 0.65 $\pm$ 0.03 (stat) $\pm$ 0.07 (syst) $\pm$ 0.02 (theo) pb for the Z $+ \geq$ 2 b jets , which are better described by the MG5\_aMC (LO) simulation but overestimated by MG5\_aMC (NLO) and SHERPA predictions. Since all predictions are normalized to an NNLO cross section, differences between MG5\_aMC (NLO) and MG5\_aMC (LO) results would be attributable to variations in shapes of observables and settings (PDFs, MC tunes, matching schemes) used in those simulations. The SHERPA simulation overestimate the measured integrated cross section, however, it provides a good description for shapes of various kinematic observables. The MG5\_aMC (LO) and MG5\_aMC (NLO) interfaced with PYTHIA describe the integrated cross section better but do not completely describe the shapes of the kinematic observables. Present measurements can be used as an input for the further optimization of the simulation parameters. The measured value of cross section ratio of the Z $+ \geq$ 2 b jets and Z $+ \geq$ 1 b jet is 0.100 $\pm$ 0.005 (stat) $\pm$ 0.007 (syst) $\pm$ 0.003 (theo), which is better described by the MG5\_aMC (LO, NNPDF 3.0, CUETP8M1) and SHERPA but overestimated by the MG5\_aMC (NLO) prediction. |
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