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

By baur han and ohnemus 1998 of 47 02 pb and the d0

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Unformatted text preview: first time at a hadron collider (Abazov et al., 2009d) and used these events to search for Z and ZZ couplings that are absent at tree level in the SM. The experimental signature for Z !  is a high-energy photon and large ET . In the analysis, events are 6 required to have a single photon candidate with ET > 90 GeV and ET > 70 GeV=c. The primary backgrounds are from 6 W ! e and events unrelated to the collision in which muons from beam halo or cosmic rays produce energetic photons 2 10 1 10 10 -1 -2 100 200 300 ET [GeV] [GeV] DØ 1fb-1 (b) DØ, 3.6 fb-1 2.0 Data Sum of backgrounds SM signal MC + backgrounds 102 eeγ dN/dET [GeV-1] Mllγ [GeV/c2] 1.5 ATGC signal MC + backgrounds 1.0 0.5 µµγ 0.0 2 10 Mll [GeV/c2] FIG. 15 (color online). The three-body mass M‘‘ vs the dilepton mass M‘‘ for Z candidate events in the D0 analysis. From Abazov et al., 2007a. Rev. Mod. Phys., Vol. 84, No. 4, October–December 2012 100 150 200 250 300 ET [GeV] FIG. 16 (color online). The observed photon ET spectrum along with the SM expectation and possible anomalous TGC scenarios for (a) Z ! ‘‘ (Abazov et al., 2007a) and (b) Z !  (Abazov et al., 2009d) channels. Hobbs, Neubauer, and Willenbrock: Tests of the standard electroweak model at . . . (a) Z γγ Λ = 1.5 TeV DØ, 3.6 fb-1 0.005 Z h40 γ h40 0.005 0 -0.005 (b) ZZγ Λ = 1.5 TeV 1491 DØ, 3.6 fb-1 0 -0.005 -0.1 -0.05 0 0.05 0.1 -0.1 γ h30 -0.05 0 0.05 0.1 hZ 30 FIG. 17. Two-dimensional bounds (ellipses) at 95% C.L. on CP-conserving (a) Z and (b) ZZ couplings. The crosses represent the onedimensional bounds at the 95% C.L. setting all other couplings to zero. The dashed lines indicate the unitarity limits for à ¼ 1:5 TeV. From Abazov et al., 2009d. for the photon ET > 90 GeV, consistent with the NLO cross section of 39 Æ 4 fb (Baur, Han, and Ohnemus, 1998). Both of the CDF and D0 Z cross-section measurements are consistent with the SM expectations at NLO. D0 searches for anomalous Z and ZZ couplings using the observed photon ET spectrum in the Z ! ‘‘ (Abazov et al., 2007a) and Z !  (Abazov et al., 2009d). A LO simulation (Baur and Berger, 1993; Baur, Han, and Ohnemus, 1998) of the Z signal is used with NLO corrections (Baur, Han, and Ohnemus, 1998) applied to the photon ET spectrum. The observed photon ET spectrum along with the SM expectation and possible anomalous TGC scenarios for two channels is shown in Fig. 16. The Z ! ‘‘ and Z !  combined limits on the CP-conserving Z and ZZ couplings are shown in Fig. 17. The 1D combined limits at 95% C.L. are jh j < 0:033, jh j < 0:0017, jhZ j < 0:033, and jhZ j < 30 40 30 40 0:0017 for à ¼ 1:5 TeV. 4. WW Production of W boson pairs in hadron (and lepton) collisions involves both the WW and WWZ couplings. First evidence for W boson pair production was reported by CDF using Tevatron Run-I data (Abe et al., 1997). This process was later measured with greater R significance by D0 and CDF R using Ldt ¼ 224–252 and Ld...
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This document was uploaded on 09/28/2013.

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