RevModPhys.84.1477】Tests of the standard electroweak model at the energy frontier

Wwz coupling parameters z gz and z are constrained

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Unformatted text preview: didates DØ, 1 fb-1 Standard Model MC AC MC: ∆ κZ = ∆ gZ = -0.25, λZ = -0.25 1 AC MC: ∆ κZ = ∆ gZ = 0.50, λZ = 0.25 14 Overflow Bin Flavor classification 16 Events / 40 GeV/c TABLE XIII. Summary of the expected and observed yields for the CDF (Abulencia et al., 2007b) and D0 (Abazov et al., 2007b) WZ ! ‘‘‘ analyses. In the classification column, ‘t denotes a track-only lepton candidate having unknown flavor which is only relevant for the CDF analysis. 1495 80 100 120 140 160 Invariant Mass (GeV/c2) FIG. 24. ET vs dilepton invariant mass of WZ ! ‘‘‘ candidate 6 events in the D0 WZ analysis (Abazov et al., 2007b). The open boxes represent the expected WZ signal. The filled boxes represent the sum of the estimated backgrounds. The stars are the data that survive all selection criteria. The open circles are data that either fail the dilepton invariant mass criterion or have ET < 20 GeV. 6 Rev. Mod. Phys., Vol. 84, No. 4, October–December 2012 TABLE XIV. One-dimensional 95% C.L. intervals on Z , ÁgZ , 1 and ÁZ for two sets of form factor scale à for the D0 WZ ! ‘‘‘ analysis (Abazov et al., 2007b). à ¼ 1:5 TeV À0:18 < Z < 0:22 À0:15 < ÁgZ < 0:35 1 À0:14 < ÁZ ¼ ÁgZ < 0:31 1 à ¼ 2:0 TeV À0:17 < Z < 0:21 À0:14 < ÁgZ < 0:34 1 À0:12 < ÁZ ¼ ÁgZ < 0:29 1 Hobbs, Neubauer, and Willenbrock: Tests of the standard electroweak model at . . . 1496 1 DØ, 1 fb-1 0.6 λZ 0.2 -0.2 -0.6 -1 -1 -0.6 -0.2 ∆ κZ = 0.2 0.6 1 ∆gZ 1 FIG. 26. Two-dimensional 95% C.L. contour limit in ÁgZ ¼ ÁZ 1 vs ÁZ space (inner contour) for the D0 WZ ! ‘‘‘ analysis (Abazov et al., 2007b). The form factor scale for this contour is à ¼ 2 TeV. The physically allowed region (unitarity limit) is bounded by the outer contour. The cross hairs are the 95% C.L. one-dimensional limits. 6. ZZ The production of Z pairs is predicted within the SM to have the smallest cross section among the diboson processes. It has been observed in eþ eÀ collisions at LEP (Alcaraz et al., 2006), but not in hadron collisions as of the start of the Tevatron Run-II. As a window to new physics, ZZ production is particularly interesting because of the absence of ZZ and ZZZ couplings in the SM (see Fig. 27), and because of the very low backgrounds in the four charged-lepton channel. Higgs-boson decay can contribute to ZZ production; however, this channel is generally not competitive with H ! WW ðÃÞ as a discovery channel at the Tevatron collision energy and integrated luminosity. As is the case for WW and WZ production, the ZZ state is most easily observed in the fully leptonic mode at a hadron collider. The ZZ ! ‘‘‘‘ process is rare but predicted to be nearly background free in the SM, with Z þ jets (jets reconstructed as charged leptons) as the only non-negligible background. Having large total charged-lepton acceptance in the experiments is crucial due to the high lepton multiplicity in t...
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