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

Figs 8 and 9 show the 05 afb a 1 08 afb rest frame

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Unformatted text preview: s, and differences in the Z and couplings to quarks result in different angular distributions for the decay products for up-type (I3 ¼ þ1=2) and down-type (I3 ¼ À1=2) quarks. Together, these two effects produce mass and flavor dependence in the coefficients a and b which can be calculated assuming the SM. The forward-backward Z= Ã production charge asymmetry is defined as 1485 PYTHIA ZGRAD2 0 Statistical uncertainty Total uncertainty -0.5 50 70 100 100 300 500 Mee (GeV/c 2 ) FIG. 9 (color online). Dielectron forward-backward asymmetry as a function of dielectron mass (D0). measured asymmetries and the SM predictions as a function of mass for the CDF and D0 results, respectively. Using these measurements and the SM prediction for the coefficients a and b, sin2 eff can be determined. Here eff is W W the weak mixing angle including higher-order corrections. The current world average is sin2 eff ¼ 0:231 49 Æ 0:000 13 W TABLE V. The expected and measured asymmetries as a function of dielectron mass (D0). For the measured values, the first uncertainty is statistical and the second is systematic. Dielectron mass range [ðGeV=cÞ2 ] 50–60 60–70 70–75 75–81 81–86.5 86.5–89.5 89.5–92 92–97 97–105 105–115 115–130 130–180 180–250 250–500 AFB PYTHIA À0:293 À0:426 À0:449 À0:354 À0:174 À0:033 0.051 0.127 0.289 0.427 0.526 0.593 0.613 0.616 ZGRAD À0:307 À0:431 À0:452 À0:354 À0:166 À0:031 0.052 0.129 0.296 0.429 0.530 0.603 0.600 0.615 Measured À0:262 Æ 0:066 Æ 0:072 À0:434 Æ 0:039 Æ 0:040 À0:386 Æ 0:032 Æ 0:031 À0:342 Æ 0:022 Æ 0:022 À0:176 Æ 0:012 Æ 0:014 À0:034 Æ 0:007 Æ 0:008 0:048 Æ 0:006 Æ 0:005 0:122 Æ 0:006 Æ 0:007 0:301 Æ 0:013 Æ 0:015 0:416 Æ 0:030 Æ 0:022 0:543 Æ 0:039 Æ 0:028 0:617 Æ 0:046 Æ 0:013 0:594 Æ 0:085 Æ 0:016 0:320 Æ 0:150 Æ 0:018 Rev. Mod. Phys., Vol. 84, No. 4, October–December 2012 using the modified minimal subtraction (MS) scheme (Amsler et al., 2008). Among the measurements used for the world average are two, the charge asymmetry for b-quark production (Abbiendi et al., 2006b) from LEP and SLD and the measurement from NuTeV (Zeller et al., 2002), which differ from the world average by more than 2 standard deviations. The values for sin2 eff extracted using fits to the AFB W distributions are sin2 eff ¼ 0:2238 Æ 0:0040ðstatÞ Æ 0:0030ðsystÞ W for CDF and sin2 eff ¼ 0:2327 Æ 0:0018ðstatÞ Æ 0:0006ðsystÞ W for D0. Figure 10 shows these results compared to other measurements. The results from D0 are comparable in precision to other measurements for light quarks. The current Tevatron results are limited by sample statistics, but by the end of the Tevatron running, CDF and D0 are expected to Hobbs, Neubauer, and Willenbrock: Tests of the standard electroweak model at . . . 1486 0.23149 ± 0.00013 [a] PDG ’08 0, l 1 0.8 Al(Pτ) 0.2316 ± 0.0004 [b] 0.6 Al (SLD) 0.2310 ± 0.0003 [b] 0.4 0, b Afb 0.2322 ± 0.0003 [b] 0.2 0, c Afb 0.2322 ± 0...
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