400
22. The GSW Gauge Theory of Electroweak Interactions
FIGURE 22.22
The W decay angular distribution of the emission angle θ
∗ of the positron
e
(electron) with respect to the antiproton (proton) beam direction, in the rest
frame of the W, for a total of 75 events; background subtracted and acceptance
corrected (Arnison et al. 1986).
(22.77) to M W ⋍ 80.38 GeV (Nakamura et al. 2010). We show in figure 22.21
a later determination of M W by the CDF collaboration (Abe et al. 1995a).
The W and Z mass values may be used together with (22.42) to obtain
sin
2 θ W via
sin
2 θ W = 1 − M W
2 /M Z
2 .
(22.117)
The weighted average of UA(1) and UA(2) yielded
sin
2 θ W = 0.212 ± 0.022 (stat.).
(22.118)
Radiative corrections have in general to be applied, but one renormalization
scheme (see section 22.6) promotes (22.117) to a definition of the renormalized
sin
2 θ W to all orders in perturbation theory. Using this scheme and quoted
values of M W , M Z (Nakamura et al. 2010) one finds sin
2 θ W ⋍ 0.223.
Finally, figure 22.22 shows (Arnison et al. 1986) the angular distribution of
the charged lepton in W → eν decay (see section 22.4.2); θ
∗ is the e
+ (e
− ) angle
e