Subatomic Physics

252 P , C, CP, andT
The result,
〈H(e − )〉 = − v
c ,
〈H(e + )〉 =+ v
c ,
(9.34)
where v is the lepton velocity,
confirms parity nonconservation
in the weak interaction.
We have stated above that
parity is conserved in the electromagnetic
and the hadronic
interaction. This statement
requires some explanations.
Neglecting the gravitational
interaction, the total Hamiltoniancanbewrittenas
H = Hh + Hem + Hw.
Figure 9.6: (a) Arrangement to measure beta emission
from polarized nuclei. (b) Result of the earliest experiment
showing parity nonconservation [C. S. Wu, E. Ambler,R.W.Hayward,D.D.Hoppes,andR.P.Hudson,
Phys. Rev. 105, 1413 (1957).] A normalized counting rate
in the beta detector is shown for two directions of the external
magnetic field. After adiabatic demagnetization, the
source warms up, the polarization decreases, and the effect
disappears.
Cross sections or transition probabilities are always proportional to |H| 2 ;consequently
interference terms between the weak and the other two interactions will
occur. Since Hw does not conserve parity, the interference terms should also show
parity violation. Experiments to detect these interference terms are extremely difficult,
but parity violating asymmetries of the expected order of magnitude have indeed
been seen in many experiments. (12) The interference of the weak and hadronic
interactions has been observed in nuclear reactions, radiative transitions and in
nucleon–nucleon scattering. The effect for the electromagnetic interaction has been
verified in atomic physics, (13) in electron-electron scattering, (14) and in polarized
electron- proton and -nucleus scattering (15) experiments.
9.4 Charge Conjugation
In Section 5.10, the concept of antiparticles was introduced. This concept gives
rise to long and mainly philosophical discussions centered around questions such as
Phys. Rev. 109, 1015 (1958).
12E. G. Adelberger and W. Haxton, Annu. Rev. Nucl. Part. Sci. 35, 501 (1985); E. M. Henley
in Prog. Part. Nucl. Phys., (A. Faessler, ed.) 20, 387 (1987); W. Haeberli and B.R. Holstein in
Symmetries and Fundamental Interactions, ed. W.C. Haxton and E.M. Henley, World Scientific
Singapore, 1995, p. 17.
13E. A. Hinds, Amer. Sci. 69, 430 (1981); E. N. Fortson and L. L. Lewis, Phys. Rept 113, 289
(1984); M. C. Noecker, B. P. Masterson, and C. E. Wieman, Phys. Rev. Lett. 61, 310 (1988).
14P.L. Anthony et al., SLAC E158 Collaboration, Phys. Rev. Lett. 92, 181602 (2004).
15C.Y. Prescott et al., Phys. Lett. 77B, 347 (1978), 84B, 524 (1979); T. M. Ito et al. (SAMPLE
Collaboration), Phys. Rev. Lett. 92, 102003 (2004); K.A. Aniol et al. (HAPPEX Collaboration),
Phys. Rev. C 69, 065501 (2004); D. S. Armstrong et al. (G0 Collaboration), Phys. Rev. Lett.
95, 092001 (2005).