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

Bin this function includes the effects of resolution

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Unformatted text preview: events generated using ALPGEN (Mangano et al., 2003). The CDF result does not have a single dominant source of systematic uncertainty. Although the contributions vary somewhat, the uncertainties arising from jet calibration, the background prediction, and modeling of final-state radiation are roughly equivalent to each and provide most of the systematic uncertainty. C. Single-top production and Vtb The top quark was first observed in reactions mediated by " " the strong interaction process pp ! tt (Abachi et al. (1995) and Abe et al. (1995), and nearly all measurements of the top-quark properties have been made using such events. Rev. Mod. Phys., Vol. 84, No. 4, October–December 2012 FIG. 45. The s-channel (left) and t-channel (right) diagrams for single-top production. However, top quarks can also be produced singly via the s-channel (Cortese and Petronzio, 1991; Stelzer and Willenbrock, 1995; Heinson et al., 1997) and t-channel (Willenbrock and Dicus, 1986; Yuan, 1990; Ellis and Parke, 1992; Heinson et al., 1997) electroweak diagrams shown in Fig. 45. These production modes involve the Wtb coupling and therefore cross-section measurements provide previously unmeasured information on the electroweak sector, particularly the CKM matrix element Vtb . In addition to providing information about Vtb , detecting these events demonstrates progress toward Higgs sensitivity for the WH associated production mode with the subsequent decay H ! bb. The NLO cross sections for these processes are s ¼ 1:12 Æ 0:05 pb and t ¼ 2:34 Æ 0:13 pb (Smith and Willenbrock, 1996; Stelzer, Sullivan, and Willenbrock, 1997; Harris et al., 2002; Campbell, Ellis, and Tramontano, 2004; Sullivan, 2004; Cao et al., 2005; Cao, Schwienhorst, and Yuan, 2005; Frixione et al., 2006; Kidonakis, 2006; Campbell et al., 2009) for the s-channel and t-channel reactions, respectively, assuming jVtb j ¼ 1 and a top-quark mass of Mt ¼ 175 GeV=c2 . While the total " single-top cross section is slightly more than 40% of the tt cross section, the reduced parton multiplicity in the single-top events implies a signal-to-noise ratio which is roughly " 25 times lower than in tt making these events much more difficult to identify. In the SM with three generations, existing measurements of jVub j and jVcb j tightly constrain jVtb j to almost exactly unity (Amsler et al., 2008). If there are more than three generations, however, jVtb j is almost entirely unconstrained. Both D0 and CDF have long histories of searching for single-top production. The most recent results from both D0 (Abazov et al., 2007d, 2008h) and CDF (Aaltonen et al., 2008d) give clear evidence for single-top production and include results for the cross section and the CKM element jVtb j. The D0 analysis uses a data sample corresponding R to Ldt ¼ 2:3 fbÀ1 . The CDF analysis uses up to R Ldt ¼ 3:2 fbÀ1 . Candidate single top events are selected in the lepton þ jets channel in which the W decays via...
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This document was uploaded on 09/28/2013.

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