introduction-weak-interaction-volume-one

and
(5 .6 .26) might still be absent from the total Hamiltonian . Thus there
exist two separate possibilities : first, the Hamiltonian contains onl y
charged-current terms, and its Al
= 3/2 is suppressed by the strong
interaction ; and second, the Hamiltonian does, in fact, involve neutral
lepton currents with a strength comparable to that of the charged lepto n
currents . We now examine the predictions of these two models . Both indicat e
weak .AY = 0 hadron interactions . Assuming the Cabibbo form of universality
(5 .6 .5), (5 .6 .9) become s
HI (QY = 0) = -( G/ .!2") (cos2 e(Jr(l,l) J0(1,—1))
-
whereas (5.6.22) yields
HI (AY = 0)
+ sin2 6 (Jr(+, ) 5 .(+,—) ) ) , (5 .6.27 )
-(G/4Q) (cos20 (Jr(l,l )
a'Dr(l,-.1) - ( J0 ,0 ( 1 ,0 ) J
0r,0(1,0)
J
J°0(0,0) JT0 0 (1,0) +
r ,
sin2 e (Jr(+,+) Jr(-,- )
~ O ( r"~) Jr ,O(+4) ) ) (5.6.28 )
r
AY = 0 weak interactions are usually difficult to study experimentally
because they are masked by strong interactions with a much larger amplitude .
However, weak effects do give rise to parity-violating nuclear transitions,
so that a nuclear state K no longer possesses a well-defined parity, bu t
consists of a mixture of parities :
1K> = IK + > + f (5.6.29 )
where f is the parity-violating amplitude . From (5.6 .27) or (5.6 .28) we
may predict (29 )
f 10 7 . (5 .6.30 )
Experiments use, for example, the fact that for the
excited state of Ta 181 (482 keV, 5/2 1-
a' ray connecting the
) to the 7/2 + ground state, th e
normal M1 transition matrix is suppressed by nuclear structure effect s 1° (30),
so that the parity-violating II transition matrix produces an observabl e
effect . Recent studies of the circular polarization in the gamma rays from
Tal8l and L. 175 indicate that (31 )
fTa
, J° 0 (1,0) J°0(0,0) +
r, r,
+ JT°° (°, 0 ) Jr°° (°, 0)) )
° (0 .4 - 4) x 10-7
fLu = ( 2 - 8) x 10-7
(5 .6.31 )
(5 .6.32)