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

z in which q u d are proton valence quarks the sm

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Unformatted text preview: the isospin I3 , and the sine of the weak mixing angle sin2 W . The differential cross section as a function of the direction of the fermion resulting from the Z= à decay is given by 10 1 (b) 2 0 -2 50 100 150 200 mT (GeV/c2) FIG. 6. The mT distributions used for the ÀW measurement. (a) The CDF W !  channel. (b) The CDF W ! e channel. (c) The D0 W ! e channel. d ¼ að1 þ cos2 Þ þ b cos d cos (5) in which  is the angle of the fermion from the Z= à decay measured relative to the incoming quark direction in the Z= à TABLE IV. The ÀW measurements. For the result, the first uncertainty is the statistical uncertainty and the second is the systematic uncertainty. Channel Yield Fit range (GeV=c2 ) ÀW (MeV) 2 =dof CDF W !  CDF W ! e CDF combined D0 W ! e 2619 3436 90 < mT < 200 90 < mT < 200 17=21 19=21 5272 100 < mT < 200 1948 Æ 67 Æ 71 2118 Æ 60 Æ 79 2032 Æ 45 Æ 57 2028 Æ 39 Æ 61 Rev. Mod. Phys., Vol. 84, No. 4, October–December 2012 75:2=75 Hobbs, Neubauer, and Willenbrock: Tests of the standard electroweak model at . . . 0.4 0.2 0 Z/ * + e e - MC band includes several theoretical calculations -0.2 -0.4 Statistical Total -0.6 þ À À þ þ À 40 60 100 2 10 200 300 600 2 M ee (GeV/c ) in which þ and À are the integrated cross sections for the cases cos > 0 and cos < 0, respectively. The asymmetry extracted experimentally is given by AFB ¼ AFB corrected assuming SM and using Z-quark couplings fits 0.6 Nþ À NÀ Nþ þ NÀ FIG. 8 (color online). Dielectron forward-backward asymmetry as a function of dielectron mass (CDF). (6) DØ 1.1 fb-1 = 10.6/14 χ2/d.o.f. in which Nþ and NÀ are the acceptance, efficiency, and background corrected fermion yields in the forward ðcos > 0Þ and backward ðcos < 0Þ directions, respectively. Measuring the asymmetry rather than differential cross sections allows cancellation of many systematic uncertainties, particularly those affecting the overall normalization. Measurements of the asymmetry as a function of dielectron mass have been made by both the CDF (Acosta et al., 2005a) and D0 (Abazov et al., 2008a) using the dielectron final state. R The CDF result uses a sample with Ldt ¼ 72 pbÀ1 , and the R D0 measurement uses Ldt ¼ 1:1 fbÀ1 . The selection criteria are similar to those for the Z cross section measurements although a larger dielectron mass range was selected for the asymmetry measurements. Two experimental issues of particular importance to these measurements are (1) controlling asymmetries in either detector acceptance or selection efficiency as a function of dielectron mass and (2) limiting the impact of electron charge misidentification. In Table V, the dielectron mass range and the predicted and measured values of AFB for each mass bin from the D0 measurements are shown, and Figs. 8 and 9 show the 0.5 AFB A 1 0.8 AFB rest frame. The relative Z and à contributions to the cross section vary as a function of the Z= à mas...
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