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

And at least two same avor opposite sign lepton pairs

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Unformatted text preview: electron without a track. This is done because the background from Z þ jets is much larger in candidates with a forward trackless electron. The expected signal, expected background, and observed yields are shown in Table XV. The ZZ ! ‘‘ candidates are selected from events with exactly two oppositely charged lepton candidates excluding events with forward electrons without a track which are contaminated by large W backgrounds. Aside from ZZ production, other SM processes that can lead to two high-pT leptons include events from DY, a W decay with photon (W ) or jet (W þ jets) misidentified as a lepton; and " tt, WW , and WZ production. There are 276 events after the event selection (which contains a specialized high ET to suppress primarily DY) of 6 which only 14 Æ 2 are expected to be from the ZZ ! ‘‘ process in the SM. Approximately half of the yield is Hobbs, Neubauer, and Willenbrock: Tests of the standard electroweak model at . . . 0.4 D0, 1 fb-1 (a) 0.2 f 50 0 γ Z f 40 0.2 D0, 1 fb-1 (b) 0.4 1497 0 -0.2 -0.2 -0.4 -0.4 -0.4 -0.2 0 0.2 0.4 -0.4 -0.2 γ f 40 0.4 D0, 1 fb-1 (c) 0.2 0.4 D0, 1 fb-1 (d) 0.4 0.2 Z f 50 0.2 Z f 50 0 γ f 40 0 0 -0.2 -0.2 -0.4 -0.4 -0.4 -0.2 0 0.2 0.4 -0.4 -0.2 0 0.2 0.4 γ f 50 fZ 40 FIG. 28 (color online). Limits on anomalous couplings for à ¼ 1:2 TeV for the D0 ZZ ! ‘‘‘‘ analysis (Abazov et al., 2008c): (a) f40 vs Z , (b) f vs f , (c) fZ vs fZ , and (d) f vs f Z , assuming in each case that the other two couplings are zero. The inner and outer curves f40 40 40 50 50 50 50 are the 95% C.L. 2 degree of freedom exclusion contour and the constraint from the unitarity condition, respectively. The inner cross hairs are the 95% C.L. 1 degree of freedom exclusion limits. TABLE XV. Expected and observed number of ZZ ! ‘‘‘‘ candidate events for the CDF ZZ analysis (Aaltonen et al., 2008b). The first uncertainty is statistical and the second one is systematic. Category Candidates without a trackless electron Candidates with a trackless electron ZZ Z þ jets 1:990 Æ 0:013 Æ 0:210 þ0 010 0:014À0::007 Æ 0:003 0:278 Æ 0:005 Æ 0:029 0:082þ0::089 Æ 0:016 À0 060 þ0 016 2:004À0::015 Æ 0:210 0:360þ0::089 Æ 0:033 À0 060 2 1 Total Observed Rev. Mod. Phys., Vol. 84, No. 4, October–December 2012 and the log10 ð1 À LRÞ distribution for the dileptons. The p value for the ZZ ! ‘‘ alone is 0.12 and the combined p value is 5:1  10À6 corresponding to a significance equivalent to 4.4 standard deviations. The ZZ cross section is obtained by fitting the data for the fraction of the expected 3 10 Data ZZ WZ 102 Events expected to be due to the WW process. However, ZZ ! ‘‘ and WW have different kinematic properties which are exploited to statistically separate the contribution of these two processes to the data. The approach used by CDF is identical to that used in the WW cross-section measurement described in Sec. III.E.4. An event-by-event probability density is calculat...
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