2 The CDF Experiment at Fermilab Contents - Harvard University ...

Section 2: B Mixing and CP Violation 89
6
(; )
V ud V ub
V cd V
cb
V td V
tb
V cd V
cb
arg , V tdV
tb
b bbbbbbbbbb
b
(1; 0) -
V ud V ub
arg , V cdV
cb
V td V
tb
arg , V udV ub
V cd V
cb
Many new physics scenarios (e.g. SUSY) predict alternate forms of CP violation which
would aect these measurements [25]. One possibility is that the new physics would introduce
new phases such that the measured + + would not equal 180 . These new phases would
also aect B 0 decays dierently than B s decays and thus the same angle measured with two
dierent decays could produce dierent results. Another possibility is that no new phases
would be introduced but that the magnitudes of B 0 and B s mixing would be increased such
that the measured sides of the unitarity triangle would not be consistent with the measured
angles. Thus measuring CP violation with a variety of B decays provides a rigorous test
of the Standard Model's explanation of CP violation as well as a sensitive probe for new
physics.
Mixing Induced CP Violation
The form of CP violation which is most useful for constraining the Standard Model is
due to mixing between B 0 and B 0 , or B s and B s . For nal states to which both particle
and anti-particle can decay, interference can arise due to phase dierences between the two
decay channels. Considering the decay B s ( B s ) ! D s , K + for example, the V CKM elements
for B s ! D s , K + are approximately real as are the elements for the B s ! B s mixing. But
the V CKM phase of B s ! D s , K + is approximately the angle of the unitarity triangle. The
time dependence of the B s mixing produces a time dependent CP violating parameter of
magnitude sin .
real
-
B s D , H K+ s
HHHHHj
*
real
B s