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

Limits at 95 cl are jh j 0033 jh j 00017 jhz j

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Unformatted text preview: t ¼ 184 pbÀ1 , respectively, from Run-II of the Tevatron (Abazov et al., 2005b; Acosta et al., 2005c). At LEP, WW production has been extensively studied and stringent limits on anomalous TGC were determined. At the Tevatron, much higher WW invariant masses are probed compared to LEP because of the higher accessible energies. Also, the WW final state is a promising discovery channel for the Higgs boson at both the Tevatron and the LHC. In hadron collisions, the production of W boson pairs is most easily observed in the fully leptonic decay mode WW ! ‘‘. The experimental signature of the WW signal in leptonic decay is two isolated high ET charged leptons with opposite charge and large ET from the neutrinos. 6 Both CDF and D0 measured the WW production cross section in fully leptonic decay and used their data to search for anomalous WW and WWZ couplings. In both analyses, " the dominant backgrounds are from tt, Drell-Yan processes (DY), other diboson decays, and W þ jets where the jet fakes Rev. Mod. Phys., Vol. 84, No. 4, October–December 2012 an isolated lepton. In the CDF analysis (Aaltonen et al., " 2010a), tt is suppressed by requiring no reconstructed jets with ET > 15 GeV and jj < 2:5. In the D0 analysis (Abazov et al., 2009e), the pT of the WW system, estimated from the observed charged-lepton momenta and the ET , is re6 quired to be small [ < 20 GeV=c ðeeÞ, 25 GeV=c ðeÞ, or " 16 GeV=c ðÞ] in order to suppress tt decays. " The strategy for measuring the cross section for pp ! WW þ X differs between the CDF and D0 analyses. In the D0 analysis, the WW signal yield is determined from counting the number of R events in excess of the expected SM backgrounds using Ldt ¼ 1:1 fbÀ1 , as shown in Table IX. D0 measures " ðpp ! WW þ X Þ ¼ 11:5 Æ 2:1ðstat þ systÞ Æ 0:7ðlumÞ pb (Abazov et al., 2009e), in agreement with the NLO expectation of 12:0 Æ 0:7 pb (Campbell and Ellis, 1999). In the CDF analysis, the WW signal yield is extracted from a fit to the distribution of a matrix element likelihood ratio R (LRWW ) discriminant for events using Ldt ¼ 3:6 fbÀ1 . The events which are fit are required to pass relatively loose selection criteria as compared to the selection CDF would use for a cross-section measurement based on the event yield TABLE IX. Numbers of signal and background events expected and number of events observed after the final event selection in each channel for the D0 WW cross-section measurement (Abazov et al., 2009e). Process Z= Ã ee e  ! ee= 0:27 Æ 0:20 2:52 Æ 0:56 0:76 Æ 0:36 Z= Ã !  0:26 Æ 0:05 3:67 Æ 0:46 ÁÁÁ " tt 1:10 Æ 0:10 3:79 Æ 0:17 0:22 Æ 0:04 WZ 1:42 Æ 0:14 1:29 Æ 0:14 0:97 Æ 0:11 ZZ 1:70 Æ 0:04 0:09 Æ 0:01 0:84 Æ 0:03 W 0:23 Æ 0:16 5:21 Æ 2:97 ÁÁÁ W þ jet 6:09 Æ 1:72 7:50 Æ 1:83 0:12 Æ 0:24 Multijet 0:01 Æ 0:01 0:14 Æ 0:13 ÁÁÁ WW ! ‘‘0 10:98 Æ 0:59 39:25 Æ 0:81 7:18 Æ 0:34 WW ! ‘= ! ‘‘0 1:40...
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This document was uploaded on 09/28/2013.

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