Constraining the UT angle γ by CP violation parameters in B 0 →π + π -*

We calculate the tree and penguin amplitudes in the B0→π+π-decay channel employing the perturbative QCD factorization approach. Using the amplitudes as input with the theoretical uncertainties sufficiently considered, we constrain the UT angle γ to 53°γ 70°, from the measurements of the CP violation parameters Cπ+π- and Sπ+π-in B0→π+π-. The U-spin breaking effect between B0→π+π-and B0 s →K+K-is estimated to be around 30%.