A measurement of the WZ and ZZ production cross sections using leptonic final states in 8.6 fb$^{-1}$ of $p\bar{p}$ collisions

TL;DR

The paper presents a precision measurement of WZ and ZZ production cross sections in p p̄ collisions at √s = 1.96 TeV using 8.6 fb⁻¹ of D0 data. By examining leptonic final states and normalizing to the inclusive Z cross section, the analysis reduces luminosity and lepton-identification systematics, while employing sophisticated missing-p_T estimators and neural-network discriminants to separate signal from backgrounds. The measured cross sections are σ(WZ) = 4.50 ± 0.61 (stat)^{+0.16}_{-0.25} (syst) pb and σ(ZZ) = 1.64 ± 0.44 (stat)^{+0.13}_{-0.15} (syst) pb, with the ZZ result combined with a prior ZZ measurement yielding σ(ZZ) = 1.44^{+0.35}_{-0.34} pb; both are consistent with Standard Model predictions within uncertainties. These results constitute the most precise leptonic-diboson cross sections at the Tevatron and provide essential background benchmarks for Higgs searches and new-physics constraints in diboson channels.

Abstract

We study the processes $p\bar{p} \rightarrow WZ \rightarrow \ellν\ell^+\ell-$ and $p\bar{p} \rightarrow ZZ \rightarrow \ell^+\ell^-ν\barν, where $\ell$ = $e$ or $μ$. Using 8.6 fb$^{-1} of integrated luminosity collected by the D0 experiment at the Fermilab Tevatron collider, we measure the $WZ$ production cross section to be 4.50$^{+0.63}_{-0.66} pb which is consistent with, but slightly above a prediction of the standard model. The ZZ cross section is measured to be 1.64 $\pm$ 0.46 pb, in agreement with a prediction of the standard model. Combination with an earlier analysis of the $ZZ \rightarrow \ell^+\ell^-\ell^+\ell^-$ channel yields a $ZZ$ cross section of 1.44$^{+0.35}_{-0.34}$ pb.

Figures (9)

• Figure 1: Comparison of data and simulation in the $M_{\ell \ell}$ distribution after selecting an oppositely charged pair of tight quality leptons in the (a) $e^+e^-$, (b) $\mu^+\mu^-$, and (c) $e^\pm\mu^\mp$ channels. The lower halves of the plots show the ratio of data to simulation, with the yellow band representing the systematic uncertainty (see Section \ref{['Section:Systematics']}) on the simulation.
• Figure 2: The distribution of (a-d) $E/_{T}^{\ \prime}$, (e-h) $M_{\ell \ell}$ and (i-l) the $W$ transverse mass of the $WZ$ candidate events. The $E/_{T}^{\ \prime}$ requirement is not imposed for (a-d), and the $M_{\ell \ell}$ requirement is not imposed for (e-h). The rows correspond to different sub-channels as indicated on the figures. The vertical dashed lines indicate the requirements on $E/_{T}^{\ \prime}$ and $M_{\ell \ell}$. The signal normalization is as described in Section \ref{['Section:bgd_and_signal']}.
• Figure 3: Kinematic distributions for the $WZ$$\rightarrow$$\ell \nu \ell^+\ell^-$ signal candidates after combining the different sub-channels. The following variables are shown: (a) the $E/_{T}^{\ \prime}$; (b) the invariant mass of the $Z \rightarrow \ell^+\ell^-$ decay; (c) the $W$ transverse mass; the transverse momenta of the (d) leading and (e) subleading leptons from the $Z \rightarrow \ell^+\ell^-$ decay and (f) the charged lepton from the $W$ decay; the transverse momenta of the reconstructed (g) $Z \rightarrow \ell^+\ell^-$ and (h) $W\rightarrow l\nu$ decays. The vertical dashed lines indicate the requirements on $E/_{T}^{\ \prime}$ and $M_{\ell \ell}$. The signal normalization is as described in Section \ref{['Section:bgd_and_signal']}.
• Figure 4: Illustration of the decomposition of the dilepton $p_T$ into $a_T$ and $a_L$ components.
• Figure 5: Background vs. signal efficiency for (a) $e^+e^-$ and (b) $\mu^+\mu^-$ channels after varying the requirements on variables that are sensitive to the missing transverse momentum. The requirement $a/_T'$$>$ 5 GeV is always applied.