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Measurements of the ZZ production cross sections in the 2 l 2 nu channel in proton-proton collisions at sqrt(s) = 7 and 8 TeV and combined constraints on triple gauge couplings

CMS Collaboration

TL;DR

This CMS study measures ZZ production in the $2\ell 2\nu$ channel at $\sqrt{s}=7$ and $8$ TeV, using data corresponding to 5.1 fb$^{-1}$ and 19.6 fb$^{-1}$, respectively. It extracts cross sections via a profile likelihood fit to the reduced MET distributions, finds $\sigma(pp\to ZZ)=5.1^{+1.5}_{-1.4}$ (stat) $^{+1.4}_{-1.1}$ (syst) $\pm0.1$ (lumi) pb at 7 TeV and $\sigma(pp\to ZZ)=7.2^{+0.8}_{-0.8}$ (stat) $^{+1.9}_{-1.5}$ (syst) $\pm0.2$ (lumi) pb at 8 TeV, both compatible with SM predictions including NLO QCD and NLO EW corrections. The analysis employs data-driven methods to estimate DY and non-resonant backgrounds, and accounts for extensive systematic uncertainties. It also sets limits on neutral ATGCs $f_i^V$ (with no form factor) from the dilepton $p_T$ spectrum and combines these with CMS’s prior $4\ell$ results to produce the most stringent ATGC constraints to date. The combined limits significantly improve sensitivity to ZZ$Z$ and $\gamma ZZ$ couplings, illustrating the continued agreement of measurements with the SM while constraining possible new physics in gauge-boson self-interactions.

Abstract

Measurements of the ZZ production cross sections in proton-proton collisions at center-of-mass energies of 7 and 8 TeV are presented. Candidate events for the leptonic decay mode ZZ to 2 l 2 nu, where l denotes an electron or a muon, are reconstructed and selected from data corresponding to an integrated luminosity of 5.1 (19.6) inverse femtobarns at 7 (8) TeV collected with the CMS experiment. The measured cross sections, sigma(pp to ZZ) = 5.1 -1.4 +1.5 (stat) -1.1 +1.4 (syst) +/- 0.1 (lumi) pb at 7 TeV, and 7.2 -0.8 +0.8 (stat.) -1.5 +1.9 (syst) +/- 0.2 (lumi) pb at 8 TeV, are in good agreement with the standard model predictions with next-to-leading-order accuracy. The selected data are analyzed to search for anomalous triple gauge couplings involving the ZZ final state. In the absence of any deviation from the standard model predictions, limits are set on the relevant parameters. These limits are then combined with the previously published CMS results for ZZ in 4 l final states, yielding the most stringent constraints on the anomalous couplings.

Measurements of the ZZ production cross sections in the 2 l 2 nu channel in proton-proton collisions at sqrt(s) = 7 and 8 TeV and combined constraints on triple gauge couplings

TL;DR

This CMS study measures ZZ production in the channel at and TeV, using data corresponding to 5.1 fb and 19.6 fb, respectively. It extracts cross sections via a profile likelihood fit to the reduced MET distributions, finds (stat) (syst) (lumi) pb at 7 TeV and (stat) (syst) (lumi) pb at 8 TeV, both compatible with SM predictions including NLO QCD and NLO EW corrections. The analysis employs data-driven methods to estimate DY and non-resonant backgrounds, and accounts for extensive systematic uncertainties. It also sets limits on neutral ATGCs (with no form factor) from the dilepton spectrum and combines these with CMS’s prior results to produce the most stringent ATGC constraints to date. The combined limits significantly improve sensitivity to ZZ and couplings, illustrating the continued agreement of measurements with the SM while constraining possible new physics in gauge-boson self-interactions.

Abstract

Measurements of the ZZ production cross sections in proton-proton collisions at center-of-mass energies of 7 and 8 TeV are presented. Candidate events for the leptonic decay mode ZZ to 2 l 2 nu, where l denotes an electron or a muon, are reconstructed and selected from data corresponding to an integrated luminosity of 5.1 (19.6) inverse femtobarns at 7 (8) TeV collected with the CMS experiment. The measured cross sections, sigma(pp to ZZ) = 5.1 -1.4 +1.5 (stat) -1.1 +1.4 (syst) +/- 0.1 (lumi) pb at 7 TeV, and 7.2 -0.8 +0.8 (stat.) -1.5 +1.9 (syst) +/- 0.2 (lumi) pb at 8 TeV, are in good agreement with the standard model predictions with next-to-leading-order accuracy. The selected data are analyzed to search for anomalous triple gauge couplings involving the ZZ final state. In the absence of any deviation from the standard model predictions, limits are set on the relevant parameters. These limits are then combined with the previously published CMS results for ZZ in 4 l final states, yielding the most stringent constraints on the anomalous couplings.

Paper Structure

This paper contains 23 sections, 8 equations, 3 figures, 6 tables.

Table of Contents

  1. Introduction
  2. CMS detector
  3. Simulation
  4. Event selection
  5. Background estimation
  6. Systematic uncertainties
  7. Statistical uncertainty of the simulated and control samples.
  8. Cross sections of ZZ and WZ.
  9. Acceptance.
  10. Luminosity.
  11. Lepton trigger and identification efficiency.
  12. Lepton momentum scale.
  13. Jet energy scale and resolution.
  14. b-jet veto.
  15. Pileup.
  16. ...and 8 more sections

Figures (3)

  • Figure 1: Reduced $E_{\mathrm{T}}^{\text{miss}}$ spectrum in the inclusive ${l}\xspace{l}\xspace$ (${l}\xspace = \mathrm{e}, {\mu}$) channel at 7$\,\text{Te\spaceV}$ (top) and 8$\,\text{Te\spaceV}$ (bottom), using the photon model to describe the DY contribution and NRB modeling for $\mathrm{W}$$\mathrm{W}$, $\mathrm{W}$ + jets, and top-quark production, after selections on the dilepton invariant mass and $p_{\mathrm{T}}$, jet veto, ${b}$-tagged jet veto, third lepton veto, and $\Delta\phi$($\mathbf{p_{\mathrm{T}}\xspace^{\text{miss}}}$, jet), as described in Section \ref{['sec:selection']}. The gray error band represents the statistical uncertainty in the predicted yields.
  • Figure 2: Reduced $E_{\mathrm{T}}^{\text{miss}}$ distribution in ${l}\xspace{l}\xspace$ (${l}\xspace = \mathrm{e},{\mu}$) channels, after the full selection, at 7$\,\text{Te\spaceV}$ (top) and 8$\,\text{Te\spaceV}$ (bottom). The DY and $\mathrm{W}$$\mathrm{W}$, $\mathrm{W}$+jets, and top backgrounds are estimated with data-driven methods. The gray error band includes statistical and systematic uncertainties in the predicted yields. In the bottom plots, vertical error bars and bands are relative to the total predicted yields. In all plots, horizontal error bars indicate the bin width.
  • Figure 3: Dilepton (${l}\xspace = \mathrm{e}, {\mu}$) transverse momentum distributions at 7$\,\text{Te\spaceV}$ (top) and 8$\,\text{Te\spaceV}$ (bottom). The DY and $\mathrm{W}$$\mathrm{W}$, $\mathrm{W}$+jets, and top backgrounds are estimated from control samples in data. The gray error band includes statistical and systematic uncertainties in the predicted yields. In the bottom plots, vertical error bars and bands are relative to the total predicted yields. In all plots, horizontal error bars indicate the bin width.