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

Channel abazov et al 2008d this analysis follows up

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Unformatted text preview: nd background expectations are 1:89 Æ 0:08 events and 0:14þ0::03 events, respectively. A total of three candidate À0 02 events is observed, with two in the 4e4C subchannel (‘‘C’’ refers to the number of central leptons) and one in the 4 subchannel. Figure 30 shows the distribution of the four lepton invariant mass for data and for the expected signal and background. Using a log-likelihood ratio test statistic of the yields and pseudoexperiments, the p value is determined to be -1 DØ Run II, 1.7 fb Events/50 GeV/c 2 2.5 4e data 4µ data signal background 2 1.5 1 0.5 0 100 200 300 400 500 Four lepton invariant mass (GeV/c2) FIG. 30 (color online). Distribution of four lepton invariant mass in data, expected signal, and expected background for the D0 ZZ ! ‘‘‘‘ analysis. From Abazov et al., 2008d. Rev. Mod. Phys., Vol. 84, No. 4, October–December 2012 4:3 Â 10À8 which corresponds to a 5:3 observed significance (3:7 expected). The measured cross section in the ZZ ! ‘‘‘‘ channel is ðZZ þ X Þ ¼ 1:75þ1::27 ðstatÞ Æ 0:13ðsystÞ pb: À0 86 This result is combined with the results from an independent ZZ ! ‘‘ search (Abazov et al., 2008e), and the previous ZZ ! ‘‘‘‘ analysis (Abazov et al., 2008c) taking into account the systematic uncertainty correlations between subchannels and among analyses. The resulting p value is 6:2 Â 10À9 , and the significance for observation of ZZ production increases to 5:7 (4:8 expected). This is the first observation of ZZ production at a hadron collider. The combined cross section is ðZZ þ X Þ ¼ 1:60 Æ 0:63ðstatÞþ0::16 ðsystÞ pb; À0 17 consistent with the SM expectation. 7. WV (V ¼ W , Z) The production of vector boson pairs (WW , WZ, and ZZ) has been observed at the Tevatron in decay modes where both vector bosons decay leptonically. The semileptonic decay modes where one of the vector boson decays hadronically have larger branching fraction as compared to the fully leptonic modes but significantly larger backgrounds from jets produced in association with a W boson. As a result, simple event counting above background cannot be used to observe dibosons in semileptonic decay at the Tevatron and advanced analysis techniques utilizing multivariate (MV) event classification are required to statistically separate signal from background. Analysis of the ‘jj final state provides an excellent test bed for such advanced techniques to extract small signals from large backgrounds in real hadron collision data that has great relevance to Higgs-boson (e.g., " WH ! ‘bb) and new physics searches in final states involving jets. In addition, semileptonic diboson decay can provide a more sensitive search for anomalous trilinear gauge couplings than fully leptonic decay modes since anomalous TGCs enhance production at high gauge boson momentum where the signal-to-background ratio improves. The dijet mass resolution of the CDF and D0 detectors is not good eno...
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This document was uploaded on 09/28/2013.

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