Decay processes which involve the interference of b→c
and b→u transitions give access to the CKM angle γ.
When these processes involve only tree level diagrams it is a very good
assumption that there is no significant contribution from processes beyond
the Standard Model.
Therefore a measurement of γ from such decays provides a 'benchmark'
value against which other measurements, more sensitive to new physics
contributions, can be compared.
The BaBar and Belle experiments presently measure γ in this manner
with an uncertainty of around
30°.
LHCb has the potential to improve this sensitivity by an order of
magnitude.
A very promising example of this approach is the family
of decays B → D K, as illustrated below.
Interference occurs if the D and the Dbar are reconstructed
in the same final state, such as K+K- or
K+π-.
