9 Symmetry Violations and Quark Flavour Physics
537
contribution from a top quark loop, with a weak coupling V ∗
tb V ts and an isospin1/2 (Kπ) state. The tree diagram for b → u + (us) has a coupling V ∗
ub V us and
leads to I = 1/2 or 3/2 states. The observed quantity is the decay asymmetry:
a =
N(B 0 → K − π + ) − N(B 0 → K + π − )
N(B 0 → K − π + ) + N(B 0 → K + π − )
.
(9.57)
Asymmetries in the order of 10% and 025% have been observed for the B 0 and
the B 0
s meson respectively.
3. CPviolation in the interference. Here the time dependence of the decay of an
initially pure flavor state to a final state f is different for an initial particle or
antiparticle. The final state can be a CP eigenstate such as π + π − (CP = +1)
or J/Ψ K S (CP = −1). In the kaon system the observed effect is m ε ∼ 1.6 ×
10 −3 , while in the B 0 system it is a very large asymmetry of order O(1).
9.4 Models of CP Violation
After the discovery of CP violation in K decay, a host of theoretical models
was proposed to allocate this phenomenon to known interactions. Assuming CPT
invariance of all interactions, the observed CP-violating effects in K decay imply
also T violation (the experimental data of Sect. 9.5 are even sufficient to prove T
violation without CPT invariance). In general, with CPT invariance, there are four
combinations of violations possible:
(a) T -conserving, C-violating and P-violating;
(b) T -violating, C-conserving and P-violating;
(c) T -violating, C-violating and P-conserving;
(d) T -violating, C-violating and P-violating.
Parity conservation in strong and electromagnetic interactions has been tested,
for example by looking for a circular polarization in γ rays from nuclear transitions.
The presence of a wrong-parity admixture in one of the nuclear states involved will
cause a small amplitude for a γ transition with abnormal multipolarity that can
interfere with the dominant amplitude and cause such a circular polarization. In the
experiments of Lobashov et al. [46], polarizations of the order of 10 −5 have been
measured. These are consistent with being due to the two-nucleon force np → pn
induced by the weak interaction (see [47] for a review).
From many experiments of a similar nature, one can infer that the strong and
electromagnetic interactions are not of type (a), (b) or (d). Therefore, if the source
of the CP-violating phenomena is located in the strong or the electromagnetic
interaction, there must be a part of one of those interactions that belongs to class
(c), i.e. C- and T -violating, but P-conserving.
537
contribution from a top quark loop, with a weak coupling V ∗
tb V ts and an isospin1/2 (Kπ) state. The tree diagram for b → u + (us) has a coupling V ∗
ub V us and
leads to I = 1/2 or 3/2 states. The observed quantity is the decay asymmetry:
a =
N(B 0 → K − π + ) − N(B 0 → K + π − )
N(B 0 → K − π + ) + N(B 0 → K + π − )
.
(9.57)
Asymmetries in the order of 10% and 025% have been observed for the B 0 and
the B 0
s meson respectively.
3. CPviolation in the interference. Here the time dependence of the decay of an
initially pure flavor state to a final state f is different for an initial particle or
antiparticle. The final state can be a CP eigenstate such as π + π − (CP = +1)
or J/Ψ K S (CP = −1). In the kaon system the observed effect is m ε ∼ 1.6 ×
10 −3 , while in the B 0 system it is a very large asymmetry of order O(1).
9.4 Models of CP Violation
After the discovery of CP violation in K decay, a host of theoretical models
was proposed to allocate this phenomenon to known interactions. Assuming CPT
invariance of all interactions, the observed CP-violating effects in K decay imply
also T violation (the experimental data of Sect. 9.5 are even sufficient to prove T
violation without CPT invariance). In general, with CPT invariance, there are four
combinations of violations possible:
(a) T -conserving, C-violating and P-violating;
(b) T -violating, C-conserving and P-violating;
(c) T -violating, C-violating and P-conserving;
(d) T -violating, C-violating and P-violating.
Parity conservation in strong and electromagnetic interactions has been tested,
for example by looking for a circular polarization in γ rays from nuclear transitions.
The presence of a wrong-parity admixture in one of the nuclear states involved will
cause a small amplitude for a γ transition with abnormal multipolarity that can
interfere with the dominant amplitude and cause such a circular polarization. In the
experiments of Lobashov et al. [46], polarizations of the order of 10 −5 have been
measured. These are consistent with being due to the two-nucleon force np → pn
induced by the weak interaction (see [47] for a review).
From many experiments of a similar nature, one can infer that the strong and
electromagnetic interactions are not of type (a), (b) or (d). Therefore, if the source
of the CP-violating phenomena is located in the strong or the electromagnetic
interaction, there must be a part of one of those interactions that belongs to class
(c), i.e. C- and T -violating, but P-conserving.