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Measurement of the cross-section for W boson production in association with b-jets in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector

The ATLAS Collaboration

TL;DR

This ATLAS study measures the W boson production in association with b-jets in 7 TeV pp collisions using 4.6 fb$^{-1}$, performing both inclusive fiducial and differential cross-section measurements as a function of the leading b-jet $p_T$ in 1- and 2-jet final states. A data-driven background estimation strategy, complemented by MC templates, is combined with a robust unfolding procedure to extract fiducial cross-sections and differential distributions, including and excluding single-top contributions. The results are in agreement with NLO QCD calculations within uncertainties, and the analysis provides a detailed accounting of systematic effects, DPI corrections, and non-perturbative modeling relevant for W+$b$-jets as a background to Higgs-related processes. These measurements test perturbative QCD with heavy flavors and offer essential inputs for modeling backgrounds in Higgs and beyond-Standard-Model searches at the LHC.

Abstract

This paper reports a measurement of the W+b-jets production cross-section in proton-proton collisions at a centre-of-mass energy of 7 TeV at the LHC. These results are based on data corresponding to an integrated luminosity of 4.6 fb-1, collected with the ATLAS detector. Cross-sections are presented as a function of jet multiplicity and of the transverse momentum of the leading b-jet for both the muon and electron decay modes of the W boson. The W+b-jets cross-section, corrected for all known detector effects, is quoted in a limited kinematic range, using jets reconstructed with the anti-k_t clustering algorithm with transverse momentum above 25 GeV and rapidity within +/- 2.1. Combining the muon and electron channels, the fiducial cross-section for W+b-jets is measured to be 7.1 +/- 0.5 (stat) +/- 1.4 (syst) pb, consistent with next-to-leading order QCD calculations within 1.5 standard deviations.

Measurement of the cross-section for W boson production in association with b-jets in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector

TL;DR

This ATLAS study measures the W boson production in association with b-jets in 7 TeV pp collisions using 4.6 fb, performing both inclusive fiducial and differential cross-section measurements as a function of the leading b-jet in 1- and 2-jet final states. A data-driven background estimation strategy, complemented by MC templates, is combined with a robust unfolding procedure to extract fiducial cross-sections and differential distributions, including and excluding single-top contributions. The results are in agreement with NLO QCD calculations within uncertainties, and the analysis provides a detailed accounting of systematic effects, DPI corrections, and non-perturbative modeling relevant for W+-jets as a background to Higgs-related processes. These measurements test perturbative QCD with heavy flavors and offer essential inputs for modeling backgrounds in Higgs and beyond-Standard-Model searches at the LHC.

Abstract

This paper reports a measurement of the W+b-jets production cross-section in proton-proton collisions at a centre-of-mass energy of 7 TeV at the LHC. These results are based on data corresponding to an integrated luminosity of 4.6 fb-1, collected with the ATLAS detector. Cross-sections are presented as a function of jet multiplicity and of the transverse momentum of the leading b-jet for both the muon and electron decay modes of the W boson. The W+b-jets cross-section, corrected for all known detector effects, is quoted in a limited kinematic range, using jets reconstructed with the anti-k_t clustering algorithm with transverse momentum above 25 GeV and rapidity within +/- 2.1. Combining the muon and electron channels, the fiducial cross-section for W+b-jets is measured to be 7.1 +/- 0.5 (stat) +/- 1.4 (syst) pb, consistent with next-to-leading order QCD calculations within 1.5 standard deviations.

Paper Structure

This paper contains 14 sections, 1 equation, 9 figures, 10 tables.

Table of Contents

  1. Introduction
  2. The ATLAS detector
  3. Simulated event samples
  4. Data sample and event selection
  5. Signal and background estimation
  6. Multijet background
  7. $t\bar{t}$ background
  8. Single-top background
  9. $W$+jets backgrounds and signal
  10. Cross-section extraction
  11. Systematic uncertainties
  12. Results
  13. Results without single-top subtraction
  14. Conclusions

Figures (9)

  • Figure 1: Overlay of the $W$+$b$- jets, $W$+$c$- jets and $W$+light-jets CombNN distributions in MC simulation for $b$-tagged (CombNN $> 2.2$) jets in the muon 1-jet analysis region.
  • Figure 2: distributions in data and MC simulation in the 1-jet (top) and 2-jet (bottom) analysis regions, in the muon (left) and electron (right) channels. MC samples are normalized to the results of the multijet background fit. To enhance the multijet contribution in the fitted region, the $m_{\mathrm{T}}(W)$ selection is loosened from 60 to 40 .
  • Figure 3: CombNN distributions for the $b$-tagged (CombNN$~ > 2.2$) jet in the "at least 4 jets 1-$b$-tag" control region (top) and number-of-jets distributions in the "at least 1 jet 1-$b$-tag" region (bottom) in data and MC simulation. The muon (electron) channel is shown on the left (right). MC samples are normalized to the results of the respective ML fits.
  • Figure 4: Overlay of the $W$+jets, and single-top $m(Wb)$ distributions in MC simulation in the muon 2-jet analysis region.
  • Figure 5: Distributions of $m(Wb)$ in the 2-jet region in data and MC simulation for the muon (left) and electron (right) channels. The MC samples are normalized to the results of the respective ML fits.
  • ...and 4 more figures