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

and et 6 t the jj nal state search has signal

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Unformatted text preview: idate events are initially selected by requiring at least one trigger from a set of single muon and muon plus jet triggers. The initial offline selection requires a muon with pT > 12 GeV=c and  < 2:0, a hadronic  lepton decay candidate with a minimum transverse energy from 15 to 20 GeV (again depending on topology) and at least two jets with pT > 15 GeV=c and j < 2:5. No b-jet 5 -1 DØ 1 fb (a) Entries per 12 GeV 35 Data 4 W+jets Z+jets 3 Multijet 2 Top Diboson 1 Higgs x 30 0 50 100 150 200 250 300 Dijet mass (GeV) 16 (b) 14 Entries per 0.05 Limit / σ(pp→(W/Z)H)×BR(H→bb) 1520 -1 DØ 1 fb 12 10 8 6 4 2 0 0.2 0.4 0.6 0.8 1 NN output FIG. 62 (color online). (a) The dijet invariant mass distribution for the D0 VH ! bb search, and (b) the NN output for the VH ! jj search. Hobbs, Neubauer, and Willenbrock: Tests of the standard electroweak model at . . . TABLE XXXIX. Expected and observed 95% C.L. signal crosssection upper limits for the D0 VH ! bb and VH ! jj searches. The limits are given as a ratio of the cross-section limit to the SM cross-section prediction. MH (GeV=c2 ) bb Exp. Obs. 105 115 125 135 33 42 62 105 27 35 60 106 jj Exp. Obs. 39 43 60 87 Combined Exp. Obs. 36 47 65 61 24 28 40 63 20 29 44 50 identification is used. Signal and background separation is then improved using a set of neutral networks. A separate neutral network is trained for each of the four signal sources [WH , ZH ðH ! bbÞ, ZH ðH ! Þ, and VBF], paired with " each of the main backgrounds (W þ jets, Z þ jets, tt, and multijet). In addition, separate networks are trained for low mass (105, 115, and 125 GeV=c2 ) and high mass (135, 145 GeV=c2 ) giving a total of 32 networks. Each network uses six or seven input variables chosen such that each one pffiffiffiffi individually improves the S= B when it is added as the last variable. The same choice of input variables is made at all masses for each signal and background pairing. All backgrounds except those from multijet events in which jets are misidentified as  leptons are estimated using simulated events processed through a detailed detector simulation with corrections based on comparison of data and simulated control samples. The absence of electrons and muons from direct W or Z decay results in a significantly higher multijet background in this search than in most. The multijet background is estimated from using a control data sample enriched in -like hadronic jet events. Systematic uncertainty sources include trigger efficiency, lepton and jet identification efficiencies, jet energy calibration, and production cross-section uncertainties for backgrounds determined using simulated events. As for the other analyses, systematic uncertainties are divided into those which affect only normalization and those which affect the shape. Sources affecting the normalization include the integrated luminosity, the trigger efficiency, muon identification efficiency,  lepton identification e...
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This document was uploaded on 09/28/2013.

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