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

Boson width result is obtained using the mt

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Unformatted text preview: egion where the shape and event yield are dominated by events from the high mass region of the Breit-Wigner formula with limited impact from detector resolution effects. As for the W boson mass measurement, a binned likelihood comparison of the observed spectrum to templates generated for different W boson widths is used to extract the numerical value. The W width was measured by the CDF (Aaltonen et al., 2008a) and D0 (Abazov et al., R 2009b) using Run II data. 1 The CDF result uses a data set of Ldt ¼ 0:35 fbÀR and the electron and muon final states. The D0 result uses Ldt ¼ 1 fbÀ1 and the electron final state. The D0 data set is the same one used for the W boson mass measurement. Similar dedicated simulations and processing were used for the W width measurement as were used for the W boson mass measurement. D0 used a different hadronic recoil procedure Hobbs, Neubauer, and Willenbrock: Tests of the standard electroweak model at . . . 1484 ΓW = 1948 ± 67 MeV (a) Standard Model χ2/dof [fit range] = 17/21 104 Events/5 GeV/c 2 χ2/dof [full range] = 21/29 Data W → µν MC + Background 3 D0 RunII (e) 2.028 ± 0.072 [34] CDF RunII (e+µ) D0 RunI (e) CDF RunI (e+µ) 2.032 ± 0.073 [33] 2.231 ± 0.173 [32] 2.050 ± 0.128 [31] Had. Col. Avg (2008) 10 2.056 ± 0.062 [32] Prel. LEP Avg (2006) World Avg (2008) 2.196 ± 0.084 [20-23] 2.106 ± 0.050 [38] Background: 5.7% Z → µµ 2.0% W → τν 0.3% Multijet 0.2% DIF 2 10 10 Fit Region 1 50 100 150 200 mT (µν)(GeV/c2) 1.8 Events/5 GeV/c 2 2.4 2.6 2.8 3 3.2 χ2/dof [fit range] = 19/21 10 FIG. 7. Summary of the ÀW measurements. The hadron collider average and world average results do not include the D0 result. From Abazov et al., 2009b. χ2/dof [full range] = 32/29 Data W → eν MC + Background 3 10 Background: 2.0% W → τν (Aaltonen et al., 2009c). The new procedure gives a W boson mass result consistent with the standard method. Figure 6 shows the high mass region of the mT distribution for the three channels analyzed: the CDF W !  channel, the CDF W ! e channel, and the D0 W ! e channel. The ÀW results are given in Table IV and shown in Fig. 7. The systematic uncertainties are dominated by a hadronic recoil scale and resolution uncertainties. These contribute 54 (49) MeV for the CDF W ! e (W ! ) channel and 41 MeV to the D0 result. Other important sources include the lepton scale uncertainty and background uncertainty which are one half to two thirds the size of the hadronic recoil uncertainty. 1.4% Multijet 0.2% Z → ee 102 10 Fit Region 1 50 100 150 200 mT (eν)(GeV/c2) 10 10 Events/2 GeV/c2 2.2 ΓW Direct Measurements (GeV) ΓW = 2118 ± 60 MeV (b) 4 10 10 χ 2 5 DØ, 1 fb-1 χ2/d.o.f=75.2/75 DATA FAST MC W → τν Z → ee Multijet (c) 4 3 2 D. Forward-backward asymmetry AFB Production of Z bosons at the Tevatron is dominated by the " process qq ! Z= Ã in which q ¼ u, d are proton valence quarks. The SM couplings of the Z and to quarks depend on the quark charge Q,...
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