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

Is roughly 50 of the total background in the bb

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Unformatted text preview: e systematic uncertainty is shown after the fit. Rev. Mod. Phys., Vol. 84, No. 4, October–December 2012 1522 Hobbs, Neubauer, and Willenbrock: Tests of the standard electroweak model at . . . TABLE XL. Expected and observed event yields in each channel after preselection and at the final selection for the D0 H ! WW ðÃÞ analysis (Abazov et al., 2010b). The systematic uncertainty after fitting is shown for all samples at final selection. 120 89 3871 312 267 455 23.6 5.4 430 18.8 5573 5566 <0:1 4:3 Æ 0:3 7:1 Æ 0:5 93:8 Æ 8:3 112 Æ 9 165 Æ 6 7:6 Æ 0:2 0:6 Æ 0:1 6:4 Æ 2:5 13:5 Æ 1:5 397 Æ 14 390 from VBF and VH channels, and analysis improvements such as increased charged-lepton acceptance (D0). In the D0 analysis (Abazov et al., 2010b), an integrated luminosity of 5:4 fbÀ1 is used to search for H ! WW ðÃÞ in events with two oppositely charged leptons eþ eÀ , eÆ Ç , or þ À . Electrons are required to have jj < 2:5 (< 2:0 in the eþ eÀ channel) and Ee > 15 GeV. Muons are required to T have jj < 2:0 and p > 10 GeV=c (in the þ À channel, T one of the two muons is required to have p > 20 GeV=c). In T addition, the dilepton invariant mass is required to exceed 15 GeV=c2 . Reconstructed jets are required to have Ejet > T 15 GeV and jj < 2:4; however, no jet-based event selection is applied since the number of jets in the event is used as input to an NN to help discriminate signal from background. The dilepton invariant mass after this ‘‘preselection’’ is shown in Fig. 63(a). Additional cuts are made to suppress Z= à production. These include requiring ET > 20 GeV (> 25 GeV in the 6 6 þ À channel), high-quality ET measurement, a minimum W transverse mass to be >20 GeV (> 30 GeV in the eþ eÀ channel), and azimuthal opening angle between the two leptons Áð‘; ‘Þ < 2:0 rad. To improve the separation between signal and background, a NN optimized for several mH values between 115 and 200 GeV=c2 is used in each of the three channels. Several discriminant variables are used as inputs to the NN: the transverse momenta of the leptons, a variable indicating the quality of the leptons’ identification, the transverse momentum and invariant mass of the dilepton system, minimum W transverse mass, ET , ET quality, Áð‘; ‘Þ, Áð‘1 ; ET Þ, 6 6 6 6 Áð‘2 ; ET Þ, the number of identified jets, and the scalar sum of the transverse momenta of the jets. Figure 63 shows the agreement between data and Monte Carlo simulation after final selection for the Áð‘; ‘Þ angle and the neural network output. The expected and observed event yields are shown in Table XL. No significant excess of signal-like events is observed for any test value of mH after the final selection. The NN output distributions are used to set upper limits on the SM Higgs-boson production cross section. Figure 64(a) shows a Rev. Mod. Phys., Vol. 84, No. 4, October–December 2012 Presele...
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