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| CMS-PAS-FSQ-16-008 | ||
| Measurement of the underlying event using the Drell-Yan process in proton-proton collisions at $\sqrt{s} = $ 13 TeV | ||
| CMS Collaboration | ||
| December 2016 | ||
| Abstract: This article presents a measurement of the underlying event activity, in proton-proton collisions at a centre-of-mass energy of 13 TeV, performed using inclusive Z-boson events ($\mathrm{qq} \rightarrow \mu^+\mu^-$) collected by the CMS experiment at the Large Hadron Collider. The analyzed data corresponds to an integrated luminosity of 2.1 fb$^{-1}$. The Underlying event activity is quantified in terms of charged particle multiplicity and their scalar $p_{\rm T}$ sum in different topological regions defined with respect to the azimuthal direction of the two muons coming from the decay of the Z-boson. The distributions are unfolded to stable charged-particle level and are compared with prediction from various models at a centre-of-mass energy of 13 TeV, as well as with measurements at a centre-of-mass energy of 1.96 TeV and 7 TeV by the CDF and CMS experiments. | ||
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Links:
CDS record (PDF) ;
inSPIRE record ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, JHEP 07 (2018) 032. The superseded preliminary plots can be found here. |
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| Figures | |
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Figure 1:
Unfolded distribution of (a) particle density and (b) $\Sigma {p_{\mathrm {T}}} $ density as a function of $ {p_{\mathrm {T}}} ^{\mu \mu }$ in the towards, transverse, and away regions. Error bars represent the statistical and systematic uncertainties added in quadrature. |
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Figure 1-a:
Unfolded distribution of particle density as a function of $ {p_{\mathrm {T}}} ^{\mu \mu }$ in the towards, transverse, and away regions. Error bars represent the statistical and systematic uncertainties added in quadrature. |
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Figure 1-b:
Unfolded distribution of $\Sigma {p_{\mathrm {T}}} $ density as a function of $ {p_{\mathrm {T}}} ^{\mu \mu }$ in the towards, transverse, and away regions. Error bars represent the statistical and systematic uncertainties added in quadrature. |
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Figure 2:
Comparison of unfolded distributions of (a) particle density and (b) $\Sigma {p_{\mathrm {T}}} $ density as a function $ {p_{\mathrm {T}}} ^{\mu \mu }$with various models in the away region. The predictions of madgraph + pythia8, powheg + pythia8, and powheg + herwig++ are also overlayed. The bottom panel of each plot reports the ratio of the simulation to the measured distribution. Error band in the bottom panel represent the statistical and systematic uncertainties added in quadrature. |
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Figure 2-a:
Comparison of unfolded distributions of particle density as a function $ {p_{\mathrm {T}}} ^{\mu \mu }$with various models in the away region. The predictions of madgraph + pythia8, powheg + pythia8, and powheg + herwig++ are also overlayed. The bottom panel of each plot reports the ratio of the simulation to the measured distribution. Error band in the bottom panel represent the statistical and systematic uncertainties added in quadrature. |
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Figure 2-b:
Comparison of unfolded distributions of $\Sigma {p_{\mathrm {T}}} $ density as a function $ {p_{\mathrm {T}}} ^{\mu \mu }$with various models in the away region. The predictions of madgraph + pythia8, powheg + pythia8, and powheg + herwig++ are also overlayed. The bottom panel of each plot reports the ratio of the simulation to the measured distribution. Error band in the bottom panel represent the statistical and systematic uncertainties added in quadrature. |
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Figure 3:
Comparison of unfolded distributions of (a) particle density and (b) $\Sigma {p_{\mathrm {T}}} $ density as a function $ {p_{\mathrm {T}}} ^{\mu \mu }$with various models in the transverse region. The predictions of madgraph + pythia8, powheg + pythia8, and powheg + herwig++ are also overlayed. The bottom panel of each plot reports the ratio of the simulation to the measured distribution. Error band in the bottom panel represent the statistical and systematic uncertainties added in quadrature. |
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Figure 3-a:
Comparison of unfolded distributions of particle density density as a function $ {p_{\mathrm {T}}} ^{\mu \mu }$with various models in the transverse region. The predictions of madgraph + pythia8, powheg + pythia8, and powheg + herwig++ are also overlayed. The bottom panel of each plot reports the ratio of the simulation to the measured distribution. Error band in the bottom panel represent the statistical and systematic uncertainties added in quadrature. |
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Figure 3-b:
Comparison of unfolded distributions of $\Sigma {p_{\mathrm {T}}} $ density as a function $ {p_{\mathrm {T}}} ^{\mu \mu }$with various models in the transverse region. The predictions of madgraph + pythia8, powheg + pythia8, and powheg + herwig++ are also overlayed. The bottom panel of each plot reports the ratio of the simulation to the measured distribution. Error band in the bottom panel represent the statistical and systematic uncertainties added in quadrature. |
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Figure 4:
Comparison of unfolded distributions of (a) particle density and (b) $\Sigma {p_{\mathrm {T}}} $ density as a function $ {p_{\mathrm {T}}} ^{\mu \mu }$with various models in the towards region. The predictions of madgraph + pythia8, powheg + pythia8, and powheg + herwig++ are also overlayed. The bottom panel of each plot reports the ratio of the simulation to the measured distribution. Error band in the bottom panel represent the statistical and systematic uncertainties added in quadrature. |
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Figure 4-a:
Comparison of unfolded distributions of particle density as a function $ {p_{\mathrm {T}}} ^{\mu \mu }$with various models in the towards region. The predictions of madgraph + pythia8, powheg + pythia8, and powheg + herwig++ are also overlayed. The bottom panel of each plot reports the ratio of the simulation to the measured distribution. Error band in the bottom panel represent the statistical and systematic uncertainties added in quadrature. |
png pdf |
Figure 4-b:
Comparison of unfolded distributions of $\Sigma {p_{\mathrm {T}}} $ density as a function $ {p_{\mathrm {T}}} ^{\mu \mu }$with various models in the towards region. The predictions of madgraph + pythia8, powheg + pythia8, and powheg + herwig++ are also overlayed. The bottom panel of each plot reports the ratio of the simulation to the measured distribution. Error band in the bottom panel represent the statistical and systematic uncertainties added in quadrature. |
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Figure 5:
Comparison of the UE activity measured at $\sqrt {s}=$ 13 TeV with the measurements at 7 and 1.96 TeV, by the CMS and CDF experiments, for (a) particle density in the towards region, (b) $\Sigma {p_{\mathrm {T}}} $ density in the towards region as a function of $ {p_{\mathrm {T}}} ^{\mu \mu }$. The measured data distributions are also compared with predictions of powheg + pythia8 and powheg + herwig++. The bottom panel of each plot reports the ratio of model predictions to the measurements. Error band in the bottom panel represent the statistical and systematic uncertainties added in quadrature. |
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Figure 5-a:
Comparison of the UE activity measured at $\sqrt {s}=$ 13 TeV with the measurements at 7 and 1.96 TeV, by the CMS and CDF experiments, for particle density in the towards region as a function of $ {p_{\mathrm {T}}} ^{\mu \mu }$. The measured data distributions are also compared with predictions of powheg + pythia8 and powheg + herwig++. The bottom panel of each plot reports the ratio of model predictions to the measurements. Error band in the bottom panel represent the statistical and systematic uncertainties added in quadrature. |
png pdf |
Figure 5-b:
Comparison of the UE activity measured at $\sqrt {s}=$ 13 TeV with the measurements at 7 and 1.96 TeV, by the CMS and CDF experiments, for $\Sigma {p_{\mathrm {T}}} $ density in the towards region as a function of $ {p_{\mathrm {T}}} ^{\mu \mu }$. The measured data distributions are also compared with predictions of powheg + pythia8 and powheg + herwig++. The bottom panel of each plot reports the ratio of model predictions to the measurements. Error band in the bottom panel represent the statistical and systematic uncertainties added in quadrature. |
png pdf |
Figure 6:
Comparison of UE activity measured at $\sqrt {s}=$ 13 TeV with the measurements at 7 and 1.96 TeV, by CMS and CDF experiments, for (a) particle density in the transverse region, and (b) $\Sigma {p_{\mathrm {T}}} $ density in the transverse region. The measured data distributions are also compared with predictions of powheg + pythia8 and powheg + herwig++. The bottom panel of each plot reports the ratio of model predictions to the measurements. Error band in the bottom panel represent the statistical and systematic uncertainties added in quadrature. |
png pdf |
Figure 6-a:
Comparison of UE activity measured at $\sqrt {s}=$ 13 TeV with the measurements at 7 and 1.96 TeV, by CMS and CDF experiments, for particle density in the transverse region. The measured data distributions are also compared with predictions of powheg + pythia8 and powheg + herwig++. The bottom panel of each plot reports the ratio of model predictions to the measurements. Error band in the bottom panel represent the statistical and systematic uncertainties added in quadrature. |
png pdf |
Figure 6-b:
Comparison of UE activity measured at $\sqrt {s}=$ 13 TeV with the measurements at 7 and 1.96 TeV, by CMS and CDF experiments, for $\Sigma {p_{\mathrm {T}}} $ density in the transverse region. The measured data distributions are also compared with predictions of powheg + pythia8 and powheg + herwig++. The bottom panel of each plot reports the ratio of model predictions to the measurements. Error band in the bottom panel represent the statistical and systematic uncertainties added in quadrature. |
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Figure 7:
Comparison of the UE activity measured at $\sqrt {s}=$ 13 TeV with the measurements at 7 and 1.96 TeV, by the CMS and CDF experiments, in the towards (top) and transverse (bottom) regions. Figures (a) and (c) show the particle density , whereas figures (b) and (d) show the $\Sigma {p_{\mathrm {T}}} $ density as a function of $ {p_{\mathrm {T}}} ^{\mu \mu }$. The measured data distributions are also compared with predictions of powheg + pythia8 and powheg + herwig++. Error bars represent the statistical and systematic uncertainties added in quadrature. |
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Figure 7-a:
Comparison of the UE activity measured at $\sqrt {s}=$ 13 TeV with the measurements at 7 and 1.96 TeV, by the CMS and CDF experiments, in the towards region. The Figure shows the particle density as a function of $ {p_{\mathrm {T}}} ^{\mu \mu }$. The measured data distributions are also compared with predictions of powheg + pythia8 and powheg + herwig++. Error bars represent the statistical and systematic uncertainties added in quadrature. |
png pdf |
Figure 7-b:
Comparison of the UE activity measured at $\sqrt {s}=$ 13 TeV with the measurements at 7 and 1.96 TeV, by the CMS and CDF experiments, in the towards region. The Figure shows the $\Sigma {p_{\mathrm {T}}} $ density as a function of $ {p_{\mathrm {T}}} ^{\mu \mu }$. The measured data distributions are also compared with predictions of powheg + pythia8 and powheg + herwig++. Error bars represent the statistical and systematic uncertainties added in quadrature. |
png pdf |
Figure 7-c:
Comparison of the UE activity measured at $\sqrt {s}=$ 13 TeV with the measurements at 7 and 1.96 TeV, by the CMS and CDF experiments, in the transverse region. The Figure shows the particle density as a function of $ {p_{\mathrm {T}}} ^{\mu \mu }$. The measured data distributions are also compared with predictions of powheg + pythia8 and powheg + herwig++. Error bars represent the statistical and systematic uncertainties added in quadrature. |
png pdf |
Figure 7-d:
Comparison of the UE activity measured at $\sqrt {s}=$ 13 TeV with the measurements at 7 and 1.96 TeV, by the CMS and CDF experiments, in the transverse region. The Figure shows the $\Sigma {p_{\mathrm {T}}} $ density as a function of $ {p_{\mathrm {T}}} ^{\mu \mu }$. The measured data distributions are also compared with predictions of powheg + pythia8 and powheg + herwig++. Error bars represent the statistical and systematic uncertainties added in quadrature. |
png pdf |
Figure 8:
(a) Particle density and (b) $\Sigma {p_{\mathrm {T}}} $ density, with $ {p_{\mathrm {T}}} ^{\mu \mu } < $ 5 GeV/$c$, as a function of centre-of-mass energy for data and predictions from simulations by powheg + pythia8 and powheg + herwig++. The predictions of powheg + pythia8 without MPI are also shown. Error bars represent the statistical and systematic uncertainties added in quadrature. |
png pdf |
Figure 8-a:
Particle density, with $ {p_{\mathrm {T}}} ^{\mu \mu } < $ 5 GeV/$c$, as a function of centre-of-mass energy for data and predictions from simulations by powheg + pythia8 and powheg + herwig++. The predictions of powheg + pythia8 without MPI are also shown. Error bars represent the statistical and systematic uncertainties added in quadrature. |
png pdf |
Figure 8-b:
$\Sigma {p_{\mathrm {T}}} $ density, with $ {p_{\mathrm {T}}} ^{\mu \mu } < $ 5 GeV/$c$, as a function of centre-of-mass energy for data and predictions from simulations by powheg + pythia8 and powheg + herwig++. The predictions of powheg + pythia8 without MPI are also shown. Error bars represent the statistical and systematic uncertainties added in quadrature. |
| Tables | |
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Table 1:
Summary of the systematic uncertainties on the particle and $\Sigma {p_{\mathrm {T}}} $ density. |
| Summary |
| This article presents a measurement of the UE activity using inclusive Z-boson events at a centre-of-mass energy of 13 TeV. Analyzed data corresponds to an integrated luminosity of 2.1 fb$^{-1}$. The UE activity, quantified in terms of particle and $\Sigma p_{\mathrm{T}}$ densities, is measured as a function of the resultant $p_{\mathrm{T}}$ of the two muons coming from the decay of the Z-boson. The distributions are corrected for detector effects and compared with various predictions. It is observed that madgraph and powheg, hadronized with pythia8 and CUET8PM1 tune, describe the measurements within 5%. The combination of powheg + herwig++ with tune EE5C, overestimates the measurements by 10-15%. The results obtained at 13 TeV are also compared with previous measurements at 1.96 and 7 TeV. The UE activity almost doubles, with logarithmic increase, as the collision energy increases from 1.96 to 13 TeV. Simulations nicely describe the increase in UE activity as the collision energy increases from 7 to 13 TeV but they underestimate the UE evolution from 1.96 to 7 TeV. Hence simulations need further improvements for UE modeling, especially in the energy dependence. The present measurement, in combination with previous results, will be important for the further optimization of the model parameters in various simulations. |
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