ZZ Cross Section Research Articles

Measurement of theZZproduction cross section and search for the standard model Higgs boson in the four lepton final state inpp¯collisions

We present a measurement of Z boson pair production in ppbar collisions at 1.96 TeV with 9.6 fb-1 to 9.8fb-1 of D0 data. We examine the final states with four electrons, two electrons plus two muons, and four muons. Based on selected data, the measured cross section in the mass region M(Z/gamma*) > 30 GeV is sigma(ppbar to Z/gamma* Z/gamma*)= 1.26 ^{+0.44}_{-0.36} (stat) ^{+0.17}_{-0.15} (syst) +/- 0.08 (lumi) pb; after correcting for the expected ratio of sigma(ppbar to Z/gamma* Z/gamma*) to sigma(ppbar to ZZ), we derive a cross section for ppbar to ZZ production of 1.05 ^{+0.37}_{-0.30} (stat) ^{+0.14}_{-0.12} (syst) +/- 0.06 (lumi) pb. This result is combined with a previous result from the ZZ to two charged leptons plus two neutrinos channel resulting in a combined ppbar to ZZ cross section measurement of 1.32 ^{+0.29}_{-0.25} (stat) +/- 0.12 (syst) +/- 0.04 (lumi)} pb. These measurements are consistent with the standard model expectation of 1.43 \pm 0.10 pb. We extend this analysis to search for the standard model (SM) Higgs boson between 115 and 200 GeV. At a Higgs boson mass of 125 GeV, we expect to set a limit of 43 times the SM expectation at 95% C.L., and set a limit of 42 times the SM expectation at 95% C.L.

Heavy MSSM Higgs production at the LHC and decays to WW , ZZ at higher orders

In this paper we discuss the production of a heavy scalar MSSM Higgs boson H and its subsequent decays into pairs of electroweak gauge bosons WW and ZZ. We perform a scan over the relevant MSSM parameters, using constraints from direct Higgs searches and several low-energy observables. We then compare the possible size of the pp -> H -> WW,ZZ cross sections with corresponding Standard Model cross sections. We also include the full MSSM vertex corrections to the H -> WW,ZZ decay and combine them with the Higgs propagator corrections, paying special attention to the IR-divergent contributions. We find that the vertex corrections can be as large as -30% in MSSM parameter space regions which are currently probed by Higgs searches at the LHC. Once the sensitivity of these searches reaches two percent of the SM signal strength the vertex corrections can be numerically as important as the leading order and Higgs self-energy corrections and have to be considered when setting limits on MSSM parameters.

Measurement of theWZandZZproduction cross sections using leptonic final states in8.6 fb−1ofpp¯collisions

We study the processes $p\bar{p} \rightarrow WZ \rightarrow \ell\nu\ell^+\ell-$ and $p\bar{p} \rightarrow ZZ \rightarrow \ell^+\ell^-\nu\bar{\nu}, where $\ell$ = $e$ or ${\mu}$. 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.

W and Z pair production at LEP2

The measurements of W-pair, WWγ and ZZ cross sections performed by the four experiments at the LEP collider are herein reported. The statistics collected in the period 1996-2000 amounts to about 40000 WW, 400 WWγ and 1000 ZZ events distributed over a large center-of-mass energy range of 161-209 GeV. From the WW cross section measurements, also the W branching fractions in leptons and hadrons are derived with a percent precision: BR(W→ qq) = 67.77 ± 0.18 ± 0.22% and BR(W→ lν)=10.74 ± 0.06 ± 0.07%. PACS: 12.15.Hh Determination of Kobayashi-Maskawa matrix elements – 12.15.Mm Neutral currents – 12.15.Lk Electroweak radiative corrections – 13.38.Be Decays of W bosons – 13.38.Dg Decays of Z bosons – 13.66.Fg Gauge and Higgs boson production in e-e+ interactions – 14.70.Fm W bosons – 14.70.Hp Z bosons

New scalar resonances from sneutrino-Higgs-boson mixing in supersymmetry with small lepton number (R-parity) violation

We consider new s-channel scalar exchanges in top quark and massive gauge-bosons pair production in e+e- collisions, in supersymmetry with a small lepton number violation. We show that a soft bilinear lepton number violating term in the scalar potential which mixes the Higgs and the slepton fields can give rise to a significant scalar resonance enhancement in e+e- -> ZZ, W+W- and in e+e- -> t t(bar). The sneutrino-Higgs mixed state couples to the incoming light leptons through its sneutrino component and to either the top quark or the massive gauge bosons through its Higgs component. Such a scalar resonance in these specific production channels cannot result from trilinear Yukawa-like R-parity violation alone, and may, therefore, stand as strong evidence for the existence of R-parity violating bilinears in the supersymmetric scalar potential. We use the LEP2 measurements of the WW and ZZ cross-sections to place useful constrains on this scenario, and investigate the expectations for the sensitivity of a future linear collider to these signals. We find that signals of these scalar resonances, in particular in top-pair production, are well within the reach of linear colliders in the small lepton number violation scenario.

Sneutrino–Higgs mixing in WW and ZZ production in supersymmetry with R-parity violation

We consider new s-channel scalar exchanges in e + e −→ ZZ, W + W − in supersymmetry with a small lepton number violation. We show that a small bilinear R-parity violating term which leads to sneutrino–Higgs mixing can give rise to a significant scalar resonance enhancement in e + e −→ ZZ, W + W −. We use the LEP2 measurements of the WW and ZZ cross-sections to place useful constraints on this scenario. We also find, under conservative assumptions on the relevant parameter space involved, that such an exchange of the sneutrino-like admixture in e + e −→ ZZ, W + W − may be accessible to a 500 GeV e + e − collider.

Measurement of the ZZ cross-section in e+e− interactions at 183–189 GeV

Measurements of on-shell ZZ production are described, using data collected by DELPHI in 1997 and 1998, at centre-of-mass energies s =182.6 GeV and 188.6 GeV, respectively. Results obtained in each of the final states q q ̄ q q ̄ , μ +μ −q q ̄ , e +e −q q ̄ , ν ν ̄ q q ̄ , l + l − l + l −, and ν ν ̄ l +l − are presented. The measured cross-sections for on-shell ZZ production via the tree-level doubly-resonant graphs (NC02) are: σ NC02 (182.6 GeV)=0.38±0.18 (stat)±0.04 (syst) pb, σ NC02 (188.6 GeV)=0.60±0.13 (stat)±0.07 (syst) pb. They are consistent with the Standard Model expectations of 0.25 and 0.65 pb at each energy.

WW and ZZ production in e+e− interactions at LEP2

The pair production of W and Z bosons at centre-of-mass energy from 161 GeV to 196 GeV is measured using the ALEPH detector at LEP. WW cross sections are given for different topologies of W decays into leptons and hadrons. ZZ cross sections are also given including all possible ZZ final states.

Measurement of the e +e −→ZZ production cross section at centre-of-mass energies of 183 and 189 GeV

The e +e −→ZZ cross section at s =182.7 and 188.6 GeV has been measured using the ALEPH detector. A cut-based analysis yields cross section measurements of σ ZZ (182.7 GeV )=0.11± 0.16 0.11 ( stat.)±0.04 ( syst.) pb and σ ZZ (188.6 GeV )=0.69± 0.13 0.12 ( stat.)±0.03 ( syst.) pb . A neural network-based analysis yields σ ZZ (188.6 GeV )=0.64± 0.12 0.11 ( stat.)±0.04 ( syst.) pb . These measurements are consistent with the Standard Model expectations.