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

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Unformatted text preview: 0:20 5:18 Æ 0:29 0:71 Æ 0:10 Total expected 23:46 Æ 1:90 68:64 Æ 3:88 10:79 Æ 0:58 Data 22 64 14 Hobbs, Neubauer, and Willenbrock: Tests of the standard electroweak model at . . . 1492 TABLE X. Expected number of signal (WW ) and background events along with the total number of expected and observed events in the data for the CDF WW cross-section measurement (Aaltonen et al., 2010a). Z= Ã Events 79:8 Æ 18:4 13:8 Æ 1:9 91:7 Æ 24:8 112:7 Æ 31:2 20:7 Æ 2:8 1:3 Æ 0:2 320:0 Æ 46:8 317:6 Æ 43:8 637:6 Æ 73:0 654 (Drell-Yan) WZ W W þ 1 À jet ZZ " tt Total background WþWÀ Total expected Data alone. Table X shows the expected number of signal and background events along with the observed events in the data used to fit for the signal. For each event passing the signal selection criteria, four matrix-element-based (ME) event probabilities are calculated corresponding to the production and decay processes WW ! ‘‘, ZZ ! ‘‘, W þ 1 À jet ! ‘ þ 1 À jet, and W ! ‘ þ . In the latter two processes, the jet or is assumed to have been reconstructed as a charged-lepton candidate. The event probability for a process X is given by ~ P X ð xÞ ¼ ~ 1 Z dðyÞ ~ ~~ ~ ðyÞGðx; yÞdy; ~ hi dy SM W+W 100 Events / 0.04 Process 120 Background 80 Data 60 40 20 0 0 0.1 ~ where x represents the observed lepton momenta and ET 6 ~~ vectors, Gðx; yÞ is a transfer function representing the detector ~ resolution, and ðyÞ is an efficiency function parametrized by  which quantifies the probability for a particle to be recon~ ~ structed as a lepton. The differential cross section dðyÞ=dy is calculated using leading-order matrix elements from the MCFM program (Campbell and Ellis, 1999) and integrated over all possible true values of the final-state particle four~ vectors y. The normalization factor hi is determined from the leading-order cross section and detector acceptance for each process. These event probabilities are combined into a likelihood ratio 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Matrix Element Likelihood Ratio (LR WW ) L¼ Y i  ni eÀi Y ÀS2 =2 i Á ec; ni ! c (9) where i ¼ X k Y  Exp c ð1 þ fk Sc Þ ðNk Þi ; c fk is the fractional uncertainty for the process k due to the systematic c, and Sc is a floating parameter associated with the systematic uncertainty c. The correlations of systematic uncertainties between processes are accounted for in the definition of i . The expected number of events from process Exp k in the ith bin is given by ðNk Þi . The parameter k is an overall normalization parameter for process k and is fixed to unity for all processes other than WW , for which it is freely floating. The likelihood is maximized with respect to the systematic parameters Sc and WW . The WW cross section is then given by the fitted value of WW multiplied by " NLO ðpp ! WW Þ. + (8) j where j ¼ fZZ; W þ 1 À jet; W g and kj is the relative fraction of the expected number of events for the...
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This document was uploaded on 09/28/2013.

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