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Articles Particle Physics Neutral Weak Interactions and Particle Decays (1976)
Neutral Weak Interactions and Particle Decays (1976) |
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There are two possible methods to detect NWI in . The first is to observe
parity violation, and the second to measure the weak corrections to 
.
We discuss these in turn.
.
We shall neglect final-state interactions in 
energy asymmetries can
occur only in the presence of 
violation and final state interactions
[19,20] if 
invariance holds. The
possible correlations are then [20] (
) is some spin vector, 
some momentum):
(3) must be zero, since the momenta are coplanar in this case, (1) may be measurable in the case 
, by analysing the decay electron momentum to find the polarization (9). These asymmetries may occur at the 
level in the Weinberg-Salam model.
is thought to proceed mainly by a 
intermediate state (10). Llewellyn Smith [21] obtains 
but uses a Lagrangian
which forces 
to be in an S-wave, and thus suppresses the rate by a
factor of 
. Cheng [22] considers
various vector meson dominance models, and concludes that 
. We give his
in fig. 5. Fig. 3 gives 
. We note that non-vector NWI would modify the tail of 
.
Our analysis for the NWI mechanism in 
follows closely that in subsect.
4.4 for . Now 
is not
forbidden but merely suppressed by 
. In the Weinberg-Salam model, we
obtain 
(pure weak) 
and (weak-electromagnetic interference) 
, and slightly more for tensor NWI. Probably, no decay has been observed, and the present limit is 
[23].
The electromagnetic part of 
has never been calculated: from Llewellyn
Smith's results we obtain 
. No such estimate is possible in Cheng's
model from existing calculations, since he takes 
. Experimentally 
[24] -- not far above the theoretical
estimate. NWI contributions will tend to be suppressed in 
compared to
. We obtain (weak-electromagnetic) 
.
We expect 
, 
. The
present experimental bounds are [10] 
and 
respectively.
for a purely two-photon mechanism