Measurement of W+W- and ZZ production cross sections in pp collisions at sqrt(s) = 8 TeV

TL;DR

The CMS collaboration measures W+W− and ZZ production cross sections in pp collisions at $\sqrt{s}=8$ TeV, using leptonic decay channels and data samples up to $5.3\,\mathrm{fb}^{-1}$. WW is analyzed with 3.5 fb−1 and ZZ with 5.3 fb−1, employing detailed lepton reconstruction, jet vetoes, and tau-related final states; backgrounds are constrained via data-driven control regions and MC simulations. The measured cross sections are $\sigma(pp\to W^+W^-) = 69.9 \pm 2.8\,\mathrm{(stat)} \pm 5.6\,\mathrm{(syst)} \pm 3.1\,\mathrm{(lumi)}\,\mathrm{pb}$ and $\sigma(pp\to ZZ) = 8.4 \pm 1.0\,\mathrm{(stat)} \pm 0.7\,\mathrm{(syst)} \pm 0.4\,\mathrm{(lumi)}\,\mathrm{pb}$, consistent with SM predictions. The analysis includes comprehensive systematic studies (PDFs, scales, lepton efficiencies, pileup, and luminosity) and combines eleven ZZ channels through a joint likelihood fit. These results provide the first 8 TeV diboson cross sections and validate the modeling of irreducible backgrounds for Higgs measurements at the LHC.

Abstract

The W+W- and ZZ production cross sections are measured in proton-proton collisions at sqrt(s) = 8 TeV with the CMS experiment at the LHC in data samples corresponding to an integrated luminosity of up to 5.3 inverse femtobarns. The measurements are performed in the leptonic decay modes W+W- to l' nu l'' nu and ZZ to 2l 2l', where l = e, mu and l'(l'') = e, mu, tau. The measured cross sections sigma(pp to W+W-) = 69.9 +/- 2.8 (stat.) +/- 5.6 (syst.) +/- 3.1 (lumi.) pb and sigma(pp to ZZ) = 8.4 +/- 1.0 (stat.) +/- 0.7 (syst.) +/- 0.4 (lumi.) pb, for both Z bosons produced in the mass region 60 < m[Z] < 120 GeV, are consistent with standard model predictions. These are the first measurements of the diboson production cross sections at sqrt(s) = 8 TeV.

Figures (2)

• Figure 1: Distributions for $\mathrm{W^+}\mathrm{W^-}\xspace$ candidate events of (a) the leading lepton transverse momentum $p_{\mathrm{T}}\xspace^\text{max}$, (b) the trailing lepton transverse momentum $p_{\mathrm{T}}\xspace^\text{min}$, (c) the dilepton transverse momentum $p_{\mathrm{T}}\xspace^{\ell\ell}$, and (d) the dilepton invariant mass $m_{\ell\ell}$. Points represent the data, and shaded histograms represent the $\mathrm{W^+}\mathrm{W^-}\xspace$ signal and the background processes. The last bin includes the overflow. The $\mathrm{W^+}\mathrm{W^-}\xspace$ signal is scaled to the measured cross section, and the background processes are normalized to the corresponding estimated values in Table \ref{['tab:wwselection_all']}.
• Figure 2: Distributions for ${Z}{Z}\xspace$ candidate events of (a) the four-lepton reconstructed mass for the sum of the $4\mathrm{e}, 4{\mu}$, and $2\mathrm{e}2{\mu}$ channels and (b) the sum of the $2\ell 2\tau$ channels. Points represent the data, and shaded histograms represent the expected ${Z}\xspace{Z}\xspace$ signal and the reducible background. The shapes of the signal and background are taken from the MC simulation, with each component normalized to the corresponding estimated value from Table \ref{['table:results']}. The distributions (c) and (d) demonstrate the relationship between the reconstructed ${Z}\xspace_1$ and ${Z}\xspace_2$ masses. Different symbols are used to present different decay channels.