Measurement of the D -> pipi branching fractions

Abstract

Using data from CLEO II at the Cornell Electron Storage Ring we provide a new measurement of the branching fraction for D0 --> pi+pi-, and we present the first measurements of D0 --> pi0pi0 and of D+ --> pi+pi0, which is due to an isospin changing DELTAI = 3/2 transition. From these data we extract the ratio of isospin amplitudes \A2/A0\, and the cosine of the relative phase delta = delta2 - delta0 between these amplitudes, for D --> pipi decays. Unlike the situation in kaon decay where A2 is strongly suppressed, we find \A2/A0\ = 0.72 +/- 0.13 +/- 0.11 and cos delta = 0.14 +/- 0.13 +/- 0.09.