CMS-PAS-SMP-15-002 | ||
Measurements of $\phi^*$ differential cross sections for Drell-Yan events in pp collisions at $ \sqrt{s} = $ 8 TeV | ||
CMS Collaboration | ||
June 2016 | ||
Abstract: Measurements of $\phi^*$ differential cross sections for inclusive Drell-Yan events in the dielectron and dimuon final states are presented. The kinematic variable $\phi^*$, constructed from the lepton angles, is correlated with the transverse momentum of the vector boson. The data were collected with the CMS experiment at a centre-of-mass energy of 8 TeV and correspond to an integrated luminosity of 19.7 fb$^{-1}$. The differential cross section $\mathrm{d}\sigma / \mathrm{d}\phi^*$ normalised to the total cross section within the fiducial volume is measured with a precision of about 1% and is compared with theoretical predictions. The measured spectrum, for the range $\phi^*< $ 0.1, differs from the theoretical predictions by at most 5% (ResBos), 4% (MadGraph) and 9% (POWHEG). For higher values of $\phi^*$ the deviations are as high as 9%, 5% and 18% in the three cases respectively. | ||
Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ; |
Figures | |
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Figure 1-a:
The spectrum of dilepton transverse momentum, before unfolding, in electron (a) and muon (b) channels overlaid with the distributions from POWHEG signal and background simulations normalized to luminosity. Only statistical uncertainties in data and simulation are indicated. |
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Figure 1-b:
The spectrum of dilepton transverse momentum, before unfolding, in electron (a) and muon (b) channels overlaid with the distributions from POWHEG signal and background simulations normalized to luminosity. Only statistical uncertainties in data and simulation are indicated. |
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Figure 2-a:
The $\phi ^*$ distributions, before unfolding, in the dielectron (a) and dimuon (b) final states. POWHEG signal and background simulations, normalized to luminosity, are overlaid. Only statistical uncertainties in data and simulation are indicated. |
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Figure 2-b:
The $\phi ^*$ distributions, before unfolding, in the dielectron (a) and dimuon (b) final states. POWHEG signal and background simulations, normalized to luminosity, are overlaid. Only statistical uncertainties in data and simulation are indicated. |
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Figure 3-a:
The variation of statistical and systematic uncertainties, for absolute cross section measurements, including the main components in electron (a) and muon (b) channels. The unfolding uncertainty includes those due to PDF, Monte Carlo statistics as well as possible bias in chosing a MC reference sample. The uncertainties from the background, pile-up and the electron energy scale or, the muon $p_{\mathrm{T}}$ resolution, as the case is, are combined under the label "Other". |
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Figure 3-b:
The variation of statistical and systematic uncertainties, for absolute cross section measurements, including the main components in electron (a) and muon (b) channels. The unfolding uncertainty includes those due to PDF, Monte Carlo statistics as well as possible bias in chosing a MC reference sample. The uncertainties from the background, pile-up and the electron energy scale or, the muon $p_{\mathrm{T}}$ resolution, as the case is, are combined under the label "Other". |
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Figure 4-a:
The variation of statistical and systematic uncertainties, for normalized cross section measurements, including the main components in electron (a) and muon (b) channels. The unfolding uncertainty includes those due to PDF, Monte Carlo statistics as well as possible bias in chosing a MC reference. The uncertainties from the background estimation, pile-up and the electron energy scale or, the muon $p_{\mathrm{T}}$ resolution, as the case is, are combined under the label "Other". |
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Figure 4-b:
The variation of statistical and systematic uncertainties, for normalized cross section measurements, including the main components in electron (a) and muon (b) channels. The unfolding uncertainty includes those due to PDF, Monte Carlo statistics as well as possible bias in chosing a MC reference. The uncertainties from the background estimation, pile-up and the electron energy scale or, the muon $p_{\mathrm{T}}$ resolution, as the case is, are combined under the label "Other". |
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Figure 5-a:
Absolute differential cross sections (a) and normalised differential cross sections (b) in the electron and muon channels. The horizontal band corresponds to the total uncertainty in the theoretical prediction from POWHEG : statistical, scale and PDF for the left plot and statistical and PDF for the right. The vertical bars correspond to the total uncertainty in the experimental measurements in electron and muon channels. |
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Figure 5-b:
Absolute differential cross sections (a) and normalised differential cross sections (b) in the electron and muon channels. The horizontal band corresponds to the total uncertainty in the theoretical prediction from POWHEG : statistical, scale and PDF for the left plot and statistical and PDF for the right. The vertical bars correspond to the total uncertainty in the experimental measurements in electron and muon channels. |
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Figure 6-a:
The combined absolute (a) and the normalized (b) cross sections compared to the predictions from POWHEG, MadGraph and ResBos. The horizontal band corresponds to the uncertainty in the experimental measurement. The vertical bars in the left plot correspond to the statistical, scale and PDF uncertainties in the theoretical predictions. In the right plot, the prediction from MadGraph has statistical uncertainty, POWHEG has statistical and PDF uncertainties and ResBos has statistical, scale and PDF uncertainties included. |
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Figure 6-b:
The combined absolute (a) and the normalized (b) cross sections compared to the predictions from POWHEG, MadGraph and ResBos. The horizontal band corresponds to the uncertainty in the experimental measurement. The vertical bars in the left plot correspond to the statistical, scale and PDF uncertainties in the theoretical predictions. In the right plot, the prediction from MadGraph has statistical uncertainty, POWHEG has statistical and PDF uncertainties and ResBos has statistical, scale and PDF uncertainties included. |
Summary |
The kinematic variable $\phi^*$ is based on measurements of angles and is correlated with dilepton transverse momentum $q_{\mathrm{T}}$ in Drell-Yan events. A measurement of the absolute differential cross section $\mathrm{d} \sigma / \mathrm{d} \phi^*$ and the normalized differential cross section $(1 / \sigma) \, \mathrm{d} \sigma / \mathrm{d} \phi^*$ has been presented based on 19.7 fb$^{-1}$ of pp collision data recorded by the CMS detector. These measurements, conducted in both the electron and muon channels, provide a sensitive test for theoretical predictions. The absolute cross sections are defined with respect to the kinematic requirements set upon the leptons. The normalized cross sections, for which there is no uncertainty from the measurement of integrated luminosity, are precise at the level of 1-2%. Comparisons to theoretical predictions have been made. In general the prediction from MadGraph shows better agreement with the data compared to the predictions from POWHEG and ResBos. Concerning the normalized differential cross sections, the differences with respect to the measurements for $\phi^* < $ 0.1 are at most 5% (ResBos), 4% (MadGraph) and 9% (POWHEG). For higher values of $\phi^*$ the differences are as high as 9%, 5% and 18% in the three cases respectively. In summary, none of the theoretical calculations succeed in predicting the measurements perfectly over the entire range of $\phi^*$. |
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Compact Muon Solenoid LHC, CERN |