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

Xxi a summary of anomalous neutral tgc limits for

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Unformatted text preview: ty in the top-quark pole mass is of order ÃQCD % 200 MeV, which is considerably less than the present uncertainty. A more precise definition of mass will be needed if one attempts to measure the mass to an accuracy much less than 1 GeV=c2 . Both CDF and D0 made measurements of the top-quark mass in a variety of final states and using different methods. " The general procedure is to select events consistent with tt production in either the dilepton or lepton plus jets final state. In the SM, top quarks decay via t ! Wb with a branching fraction of essentially 100%. The dilepton final state is that in " which both W bosons from the tt pair decay to leptons, and the lepton þ jets final state is that in which one W decays to leptons and the other to quarks. Measurements of the mass have also been made in the all jets final state in which both W s decay to quarks, although this offers less precision because of significantly higher backgrounds. Rev. Mod. Phys., Vol. 84, No. 4, October–December 2012 An initial selection of candidate dilepton events is made, typically requiring two high pT charged leptons, significant ET attributed to neutrinos, and at least two jets. Typical 6 thresholds for the lepton and jet transverse momenta range between 15 and 20 GeV=c. The ET is attributed to the two 6 " neutrinos from tt decay, and the thresholds are higher, ranging between 35 and 50 GeV depending on topology. The initial selection of lepton þ jets candidate events requires a single charged lepton, ET , and at least three (and 6 often four) jets. The lepton and jet thresholds are similar to the dilepton final state, but the ET threshold is typically 6 relaxed giving requirements ranging from ET > 15 to ET > 6 6 20 GeV. Because the lepton þ jets events have significant background from W þ jet events, an additional requirement that one or more of the jets is consistent with B hadron production (b tagged) is often made. The typical tagging efficiency is 50%=jet with light quark misidentification rates of roughly 1%. The probability to misidentify a charm quark induced jet as being consistent with B hadron production is roughly 15%. Actual values vary somewhat depending on the b-tagging algorithm used. The values also depend on the signal-to-background requirements of the specific analysis which allow more or less restrictive tagging requirements. Hobbs, Neubauer, and Willenbrock: Tests of the standard electroweak model at . . . 1506 TABLE XXII. Signal and background yields for preselected published results. The purity varies considerably depending on b-tagged jets are required. R Ldt Expected Estimated Channel Channel signal yield total yield ‘‘ 2 ‘‘, e ee  e þ track  þ track ‘ þ jets 1 ‘ þ jets 1.9 1 43:8 Æ 4:4 78:0 Æ 6:2 36:7 Æ 2:4 11:5 Æ 1:4 8:3 Æ 0:5 9:4 Æ 0:1 4:6 Æ 0:1 183 Æ 25 69 Æ 11 162 Æ 11 215:8 Æ 21:9 97:5 Æ 7:2 44:5 Æ 2:7 14:8 Æ 1:5 13:7 Æ 0:7 10:3 Æ 0:2 5:5 Æ 0:1 247 Æ 29 75 Æ...
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This document was uploaded on 09/28/2013.

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