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

Or z bosons could lead to a deviation of the measured

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Unformatted text preview: decaying to either W or Z bosons could lead to a deviation of the measured value of R from the SM expectation. Important systematic uncertainties such as the integrated luminosity uncertainty cancel in the measurement of R. The ratio R has been measured by the CDF (Abulencia et al., R 2007a) using Ldt ¼ 72 pbÀ1 to be mass measurements are currently the limiting factors in the indirect constraint on the Higgs-boson mass and are shown in Fig. 3. Earlier measurements of the W boson mass have been made by the LEP experiments (Abbiendi et al., 2006a; Achard et al., 2006; Schael et al., 2006; Abdallah et al., 2008) and CDF (Affolder et al., 2001) and D0 (Abazov et al., 2002a) in Run I of the Tevatron. Signal-to-background and resolution considerations dictate use of the W ! e and W !  decay modes for the W boson mass measurement at the Tevatron. The momentum R ¼ 10:84 Æ 0:15ðstatÞ Æ 0:14ðsystÞ: (a) This measurement has a precision of 1.9% and is consistent with SM expectation at NNLO of 10:69 Æ 0:08 (Hamberg, van Neerven, and Matsuura, 1991). A summary of the results are shown in Table I. The individual results are in good agreement with each other and with the prediction from theory. Even with the moderate sample sizes of these measurements, the W and Z cross section results are limited by the systematic uncertainty from the luminosity measurements. Because of this, further improvement in these measurements is not anticipated. CDF and D0 Collaborations continue to use Z-boson production to measure experimental efficiencies acceptances and cross checks on temporal or instantaneous luminosity dependence of detector response. The updated cross section results could be reinterpreted as measurements of the integrated luminosity. t W W b (b) H W W FIG. 2. Feynman diagrams showing corrections to the W boson mass from (a) the top quark and (b) the SM Higgs boson. August 2009 B. W boson mass ℏ3  1 2 ; MW ¼ pffiffiffi EM 2 =M2 Þð1 À ÁrÞ 2GF ð1 À MW Z 80.4 (3) in which MW (and later ÀW ) correspond to the parameters of a Breit-Wigner distribution with an s-dependent width. The term Ár includes the effects of radiative corrections and 2 depends on Mt and logMH , where Mt and MH are the topquark and Higgs-boson masses, respectively. Measurement of the W boson mass can be used to constrain the allowed Higgsboson mass. The precisions of the W boson and top-quark Rev. Mod. Phys., Vol. 84, No. 4, October–December 2012 68% CL mW [GeV/c 2] At tree level, the W boson mass is fully determined by the electromagnetic fine-structure constant, the weak Fermi coupling, and the cosine of the weak mixing angle. When higher-order EW corrections, like those shown in Fig. 2, are included, the expression is modified to (Sirlin, 1980) LEP2 and Tevatron (prel.) LEP1 and SLD 80.5 80.3 mH [GeV/c2] 114 300 150 ∆α 1000 175 200 mt [GeV/c 2] FIG. 3 (color online). The measured top quark and W boson masses and a band of allowed Higgs-boson masses. This includes...
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