Chinese Acad Sci, Inst High Energy Phys, Beijing 100049, Peoples R China
; CCAST, World Lab, Beijing 100080, Peoples R China
We present an algebraic isospin approach towards a more straightforward and model-independent determination of the weak phase alpha (or phi(2)) and QCD penguin pollution in B -> pi pi decays. The world averages of current experimental data allow us to impose some useful constraints on the isospin parameters of B -> pi pi transitions. We find that the magnitude of alpha (or phi(2)) extracted from the indirect CP violation in the pi(+)pi(-) mode is in agreement with the standard-model expectation from other indirect measurements, but its fourfold discrete ambiguity has to be resolved in the near future.