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Measurement of the cross-section and charge asymmetry of $W$ bosons produced in proton-proton collisions at $\sqrt{s}=8$ TeV with the ATLAS detector

ATLAS Collaboration

TL;DR

ATLAS measures the cross-sections for W+→μ+ν and W−→μ−ν production in pp collisions at 8 TeV and the associated muon-based charge asymmetry as a function of the muon pseudorapidity. The analysis uses 20.2 fb⁻¹ of data, with fiducial definitions centered on pTμ>25 GeV, |ημ|<2.4, and mT>40 GeV, and employs NNLO QCD predictions from DYNNLO across multiple PDF sets for comparison. Differential results in |ημ| and the asymmetry are obtained in a bin-by-bin, high-purity approach, with total systematic uncertainties dominated by luminosity and detector effects. The measurements demonstrate 0.8–1.5% precision on cross-sections and 0.002–0.003 precision on the asymmetry, providing significant discrimination among PDFs and improving constraints on the proton structure at high energy scales.

Abstract

This paper presents measurements of the $W^+ \rightarrow μ^+ν$ and $W^- \rightarrow μ^-ν$ cross-sections and the associated charge asymmetry as a function of the absolute pseudorapidity of the decay muon. The data were collected in proton--proton collisions at a centre-of-mass energy of 8 TeV with the ATLAS experiment at the LHC and correspond to a total integrated luminosity of $20.2~\mbox{fb$^{-1}$}$. The precision of the cross-section measurements varies between 0.8% to 1.5% as a function of the pseudorapidity, excluding the 1.9% uncertainty on the integrated luminosity. The charge asymmetry is measured with an uncertainty between 0.002 and 0.003. The results are compared with predictions based on next-to-next-to-leading-order calculations with various parton distribution functions and have the sensitivity to discriminate between them.

Measurement of the cross-section and charge asymmetry of $W$ bosons produced in proton-proton collisions at $\sqrt{s}=8$ TeV with the ATLAS detector

TL;DR

ATLAS measures the cross-sections for W+→μ+ν and W−→μ−ν production in pp collisions at 8 TeV and the associated muon-based charge asymmetry as a function of the muon pseudorapidity. The analysis uses 20.2 fb⁻¹ of data, with fiducial definitions centered on pTμ>25 GeV, |ημ|<2.4, and mT>40 GeV, and employs NNLO QCD predictions from DYNNLO across multiple PDF sets for comparison. Differential results in |ημ| and the asymmetry are obtained in a bin-by-bin, high-purity approach, with total systematic uncertainties dominated by luminosity and detector effects. The measurements demonstrate 0.8–1.5% precision on cross-sections and 0.002–0.003 precision on the asymmetry, providing significant discrimination among PDFs and improving constraints on the proton structure at high energy scales.

Abstract

This paper presents measurements of the and cross-sections and the associated charge asymmetry as a function of the absolute pseudorapidity of the decay muon. The data were collected in proton--proton collisions at a centre-of-mass energy of 8 TeV with the ATLAS experiment at the LHC and correspond to a total integrated luminosity of ^{-1}. The precision of the cross-section measurements varies between 0.8% to 1.5% as a function of the pseudorapidity, excluding the 1.9% uncertainty on the integrated luminosity. The charge asymmetry is measured with an uncertainty between 0.002 and 0.003. The results are compared with predictions based on next-to-next-to-leading-order calculations with various parton distribution functions and have the sensitivity to discriminate between them.

Paper Structure

This paper contains 12 sections, 3 equations, 5 figures, 4 tables.

Table of Contents

  1. Introduction
  2. The ATLAS detector
  3. Analysis methodology
  4. Description of the measurements
  5. Data and simulated event samples
  6. Event selection
  7. Estimation of backgrounds
  8. Obtaining the fiducial cross-sections
  9. Systematic uncertainties
  10. Theoretical predictions
  11. Results
  12. Conclusion

Figures (5)

  • Figure 1: The muon $\eta$ (top), muon (centre), and boson transverse mass (bottom) distributions of selected events with positive muons (left) and negative muons (right). The statistical uncertainties of the data points are smaller than the size of the markers.
  • Figure 2: The relative systematic uncertainty from each source for the (left) and (right) differential cross-sections as a percentage of the differential cross-section. Also shown are the total systematic and statistical uncertainties.
  • Figure 3: The systematic uncertainty from each source for the boson charge asymmetry as an absolute difference from the central value. Also shown are the total systematic and statistical uncertainties.
  • Figure 4: The $\Wplus$ (left) and $\Wminus$ (right) fiducial cross-sections, differential in muon pseudorapidity multiplied by the branching fraction for the decay into a muon and a neutrino are shown as a function of the absolute muon pseudorapidity. The data are presented with systematic and total uncertainties (the data statistical uncertainties are smaller than the size of the markers) and are compared with the predictions from DYNNLO. In the top two plots, the CT14 NNLO PDF set is used, and DYNNLO is shown with its associated total theoretical uncertainty. In the bottom two plots, the data are compared with the central values of six different PDF sets described in the text. The statistical uncertainties of the DYNNLO predictions are indicated by error bars. The ratios of the data to the corresponding prediction are shown in the lower panels.
  • Figure 5: The boson charge asymmetry as a function of absolute muon pseudorapidity. The data are presented with systematic and total uncertainties (the data statistical uncertainties are smaller than the size of the markers). In the left plot, the data are compared with the prediction from DYNNLO in which the CT14 NNLO PDF set is used. The DYNNLO prediction is also shown with its associated total theoretical uncertainty, along with the component from the PDF set. In the right plot, the data are compared with the central prediction from DYNNLO produced using a selection of PDFs. The statistical uncertainties of the DYNNLO predictions are indicated by error bars. The ratios of the data to the corresponding prediction are shown in the lower panels.