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

The two charged leptons in the nal state are of

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Unformatted text preview: ass (mH > 135 GeV=c2 ) Higgs-boson search. Cross sections are in femtobarns. 1513 This final state has the largest cross section times branching ratio of the entries shown in Table XXVIII, and it also gives the most sensitivity to Higgs-boson production for MH & 135 GeV=c2 . Both CDF (Aaltonen et al., 2009g) and D0 (Abazov et al., 2009j) carried out searches in this final state. R The currently published results for D0 use a sample of Ldt ¼ 1:0 fbÀ1 . The CDF published results R use a sample of Ldt ¼ 2:1 fbÀ1 , and preliminary results have been reported by both collaborations which use up to R Ldt ¼ 4 fbÀ1 . The search strategies used by the two collaborations in the WH channel are generally similar. The initial event selection requires one high-pT electron or muon, large ET , and two or more jets. This selection mirrors 6 the ‘, , and bb pair present in the final state. CDF requires the events to be selected by a trigger based on the presence of a high-energy electron or muon.3 The D0 analysis requires ‘ ¼ e events to be selected by single-electron or electron plus jet triggers. For the muon final state D0 uses a two phase trigger selection. In the first phase, the events are required to be selected based on at least one of a set of single-lepton or single-lepton plus jet triggers, and all yields are predicted and compared with data. After establishing agreement in this pass, the analysis is repeated allowing events to be selected by any trigger. The yield increases by an amount predicted by the inefficiency of the triggers for the first pass and all kinematic distributions remain in agreement after a simple yield scaling to 100% trigger efficiency. At this stage, the dominant event source is W þ jets with the jets arising from light quark (u, d, s, c) production. The signalto-background ratio is then improved by requiring one or two of the jets in the event to be identified as consistent with b quark production. The D0 b identification algorithm (Scanlon, 2006) uses a NN. The NN is trained and verified on a combination of data and simulation, with the critical efficiencies and misidentification rates determined from data control samples. The CDF analysis used three different b identification algorithms. Jets are b tagged by one or more algorithms based on the presence of a secondary vertex (SECVTX) (Acosta et al., 2005e), a neural network (Aaltonen et al. (2008e), or signed impact parameters (JP) (Abulencia et al., 2006b). The signal purity is greatest when two b jets are required, but this introduces significant efficiency loss compared to the case in which only one b jet is required. To gain the most sensitivity, both categories of events, single b tagged and double b tagged, are retained, but they are analyzed separately. Optimization studies indicate that for the single-tag channel, a rather restrictive tagging requirement is needed to control the background contribution from events with light-flavor (lf) jets...
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This document was uploaded on 09/28/2013.

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