B hadrons can decay through the b-->c and b-->u transitions.
The relative ratio of charmless over charmed b-hadron semileptonic decays, is proportional to the square of the ratio :

This constraint is is represented by a circle centered in (0;0) in the (ρ; η) plane. The present experimental information come from inclusive and exclusive measurements (See the Table of Inputs).

(EPS) [JPG] Bound on Rb from |Vub/Vcb| Rb = 0.387 ± 0.028 ([0.332,0.441] @ 95% Prob.)

(EPS) [JPG] bound from |Vub/ Vcb| on (ρ, η) plane