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

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

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Unformatted text preview: ugh to distinguish hadronically decaying W bosons and Z bosons. As a result, the search for diboson production in the ‘jj final state is a search for the sum of WW and WZ production. The experimental signature of the WW þ WZ signal in semileptonic decay is one isolated high Hobbs, Neubauer, and Willenbrock: Tests of the standard electroweak model at . . . -1 DØ, 1.1 fb Events / 10 GeV/c 2 3000 Data Diboson Signal W+jets Z+jets Top Multijet 2500 2000 1500 1000 500 0 0 50 100 150 200 250 300 Events / 10 GeV/c 2 Dijet Mass (GeV/c2) -1 DØ, 1.1 fb Data - Background Diboson Signal ±1 s.d. on Background 300 200 100 Data-BG-Sig stat. ⊕ syst. ET charged lepton, large ET from the neutrino produced in W 6 decay, and at least two high ET jets. In principle, one could search for SM WZ þ ZZ production in the jj‘‘ channel. Large Z þ jets backgrounds makes this a very difficult channel to observe the SM signal, although the use of b tagging can improve the sensitivity. " The use of the bb‘‘ channel to search for associated Higgsboson production is described in Sec. V.B.2. Both D0 and CDF searched for WW þ WZ production and anomalous WW , WWZ couplings in the ‘jj final state (Aaltonen et al., 2007a, 2010b; Abazov et al., 2009f, 2009g). In these analyses, W þ jets is the dominant background. " Other significant backgrounds include Z þ jets, tt, singletop quark, and QCD multijet production. Backgrounds are suppressed by requiring a minimum W transverse mass MT ðW Þ in each event, which is the transverse mass of the charged lepton and ET system. 6 The strategy for extracting the semileptonic WW þ WZ signal yield after basic event selection differs between the D0 and CDF analyses. In the D0 analysis (Abazov et al., 2009f), thirteen kinematic variables (e.g., dijet mass) demonstrating a sensitivity to distinguish signal and background are used as input to a random forest (RF) (Breiman, 2001) multivariate R event classifier using Ldt ¼ 1:1 fbÀ1 . Figure 31 shows the 1499 0 χ2 Prob = 0.45 2 0 -2 0 50 100 150 200 250 300 Dijet Mass (GeV/c2) -1 DØ, 1.1 fb Data Diboson Signal W+jets Z+jets Top Multijet Events / 0.04 2500 2000 1500 FIG. 32 (color online). For the D0 analysis, (a) the dijet mass " " distribution from the combined eqq and qq channels for data and simulated event predictions following the fit to the RF output. (b) A comparison of the extracted signal (filled histogram) to background-subtracted data (points), along with the Æ1 standard deviation (s.d.) systematic uncertainty on the background. The residual distance between the data points and the extracted signal, divided by the total uncertainty, is given at the bottom. From Abazov et al., 2009f. 1000 500 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Events / 0.04 RF Output 400 -1 DØ, 1.1 fb Data - Background Diboson Signal ±1 s.d. on Background 200 Data-BG-Sig stat. ⊕ syst. 0 χ2 Prob = 0.78 2 ðWV þ XÞ ¼ 20:2 Æ 4:5ðstat þ systÞ pb 0 -2 0 0.1 0.2...
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This document was uploaded on 09/28/2013.

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