Measurement Of The Zz Production Cross Section In Pbarp Collisions At Sqrts

The ZZ production cross section in proton-proton collisions at 13 TeV center-of-mass energy is measured using 3.2 fb–1 of data recorded with the ATLAS detector at the Large Hadron Collider. The considered Z boson candidates decay to an electron or muon pair of mass 66–116 GeV. The cross section is measured in a fiducial phase space reflecting the detector acceptance. It is also extrapolated to a total phase space for Z bosons in the same mass range and of all decay modes, giving 16.7+2.2–2.0(stat)+0.9–0.7(syst)+1.0–0.7(lumi) pb. Lastly, the results agree with standard model predictions.

The authors present a new measurement of the production cross section [sigma](pp̄ = ZZ) at a center-of-mass energy √s = 1.96 TeV, obtained from the analysis of the four charged lepton final state l+l-l`+l`- (l, l` = e or [mu]). They observe ten candidate events with an expected background of 0.37 ± 0.13 events. The measured cross section [sigma](pp̄ =ZZ) = 1.26-0.37+0.47 (stat) ± 0.14 (syst) pb is in agreement with NLO QCD predictions. This result is combined with a previous result from the ZZ = l+l- [nu][̄nu] channel resulting in a combined cross section of [sigma](pp̄ = ZZ) = 1.40-0.37+0.43 (stat) ±0.14 (syst) pb.

Measurements are reported of the WZ and ZZ production cross sections in proton-proton collisions at $\sqrt{s}$ = 8 TeV in final states where one Z boson decays to b-tagged jets. The other gauge boson, either W or Z, is detected through its leptonic decay (either $W \to e\nu, \mu\nu$ or $Z \to e^+ e^-, \mu^+ \mu^-$, or $\nu\bar{\nu})$. The results are based on data corresponding to an integrated luminosity of 18.9 inverse-femtobarns collected with the CMS detector at the Large Hadron Collider. The measured cross sections, $\sigma(pp \to WZ)$ = 30.7 $\pm$ 9.3 (stat.) $\pm$ 7.1 (syst.) $\pm$ 4.1 (th.) $\pm$ 1.0 (lum.) pb and $\sigma(pp \to ZZ)$ = 6.5 $\pm$ 1.7 (stat.) $\pm$ 1.0 (syst.) $\pm$ 0.9 (th.) $\pm$ 0.2 (lum.) pb, are consistent with next-to-leading order quantum chromodynamics calculations.

Here, four-lepton production in proton–proton collisions, pp→(Z/?*)(Z/?*)→l+l–l'+l'–,where l,l'=e or ?, is studied at a center-of-mass energy of 13 TeV with the CMS detector at the LHC. The data sample corresponds to an integrated luminosity of 2.6 fb–1. The ZZ production cross section, ?(pp → ZZ)=14.6–1.8+1.9(stat)–0.3+0.5(syst)±0.2(theo)±0.4(lumi)pb, is measured for events with two opposite-sign, same-flavor lepton pairs produced in the mass region 60msublsup+/suplsup–/sup/sub,ml'sup+/supl'sup–/sup120 GeV60mlsup+/suplsup–/sup,ml'sup+/supl'sup–/sup120 GeV. The Z boson branching fraction to four leptons is measured to be B(Z→lsup+/suplsup–/supl'sup+/supl'sup–/sup)=4.9sub–0.7/subsup+0.8/sup (stat)sub–0.2/subsup+0.3/sup (syst)–0.1+0.2(theo)±0.1(lumi)×10sup–6/sup for the four-lepton invariant mass in the range 80mlsup+/suplsup–/supl'sup+/supl'sup–/sup100 GeV80mlsup+/suplsup–/supl'sup+/supl'sup–/sup

Four-lepton production in proton-proton collisions, pp to (Z/gamma*)(Z/gamma*) to l+l-l'+l'-, where $l, l' = e or mu, is studied at a center-of-mass energy of 13 TeV with the CMS detector at the LHC. The data sample corresponds to an integrated luminosity of 2.6 inverse femtobarns. The ZZ production cross section, sigma(pp to ZZ) = 14.6 +1.9/-1.8 (stat) +0.5/-0.3 (syst) +/- 0.2 (theo) +/- 0.4 (lumi) pb, is measured for events with two opposite-sign, same-flavor lepton pairs produced in the mass region 60 m[l+l-], m[l'+l'-]

Measurements of the ZZ production cross sections in proton-proton collisions at center-of-mass energies of 7 and 8 TeV are presented. We found that candidate events for the leptonic decay mode ZZ 2!2l2[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)fb-1 at 7 (8) TeV collected with the CMS experiment. The measured cross sections, [sigma](pp 2!ZZ)=5.1+1.5-1.4(stat)+1.4-1.1(syst)"0.1(lumi)pb at 7 TeV, and 7.2+0.8-0.8(stat)+1.9-1.5(syst)"0.2(lumi)pb at 8 TeV, are in good agreement with the standard model predictions with next-to-leading-order accuracy. Furthermore, 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. As a result, these limits are then combined with the previously published CMS results for ZZ in 4l final states, yielding the most stringent constraints on the anomalous couplings.

The WZ production cross section in proton-proton collisions at sqrt(s) = 13 TeV is measured with the CMS experiment at the LHC using a data sample corresponding to an integrated luminosity of 2.3 inverse femtobarns. The measurement is performed in the leptonic decay modes WZ to l nu l' l', where l, l'= e, mu. The measured cross section for the range 60

We report the first measurement of the cross section for Z boson pair production at a hadron collider. This result is based on a data sample corresponding to 1.9 fb−1 of integrated luminosity from p{bar p} collisions at √s = 1.96 TeV collected with the CDF II detector at the Fermilab Tevatron. In the lll′l′ channel, we observe three ZZ candidates with an expected background of 0.096{sub -0.063}{sup +0.092} events. In the ll?? channel, we use a leading-order calculation of the relative ZZ and WW event probabilities to discriminate between signal and background. In the combination of lll′l′ and ll?? channels, we observe an excess of events with a probability of 5.1 x 10−6 to be due to the expected background. This corresponds to a significance of 4.4 standard deviations. The measured cross section is?(p{bar p} →ZZ) = 1.4{sub -0.6}{sup +0.7} (stat.+syst.) pb, consistent with the standard model expectation.

The production of a Z boson, decaying into two leptons and produced in association with one or more b jets, is studied using proton-proton collisions delivered by the LHC at a centre-of-mass energy of 7 TeV. The data were recorded in 2011 with the CMS detector and correspond to an integrated luminosity of 5 fb-1. The Z(ll) + b-jets cross sections (where ll = [mu][mu] or ee) are measured separately for a Z boson produced with exactly one b jet and with at least two b jets. In addition, a cross section ratio is extracted for a Z boson produced with at least one b jet, relative to a Z boson produced with at least one jet. The measured cross sections are compared to various theoretical predictions, and the data favour the predictions in the five-flavour scheme, where b quarks are assumed massless. The kinematic properties of the reconstructed particles are compared with the predictions from the MadGraph event generator using the pythia parton shower simulation.

The top-quark pair production cross section is measured in final states with one electron or muon and one hadronically decaying [tau] lepton from the process $t\bar{t}$ to (l[nu]l) ([tau][nu][tau]) $b\bar{b}$, where l = e, [mu]. The data sample corresponds to an integrated luminosity of 19.6 fb-1 collected with the CMS detector in proton-proton collisions at $\sqrt{s}$ =8 TeV. The measured cross section [sigma]$t\bar{t}$ = 257 ± 3 (stat) ± 24 (syst) ± 7 (lumi) pb, assuming a top-quark mass of 172.5 GeV, is consistent with the standard model prediction.