Dalitz analysis of D⁰→K−π+η decays at Belle

We present the results of the first Dalitz plot analysis of the decay D0→K−π+η. The analysis is performed on a data set corresponding to an integrated luminosity of 953 fb−1 collected by the Belle detector at the asymmetric-energy e+e− KEKB collider. The Dalitz plot is well described by a combination of the six resonant decay channels K¯∗(892)0η, K−a0(980)+, K−a2(1320)+, K¯∗(1410)0η, K∗(1680)−π+ and K∗2(1980)−π+, together with Kπ and Kη S-wave components. The decays K∗(1680)−→K−η and K∗2(1980)−→K−η are observed for the first time. We measure ratio of the branching fractions, B(D0→K−π+η)/B(D0→K−π+)=0.500±0.002(stat)±0.020(syst)±0.003(BPDG). Using the Dalitz fit result, the ratio B(K∗(1680)→Kη)B(K∗(1680)→Kπ) is measured to be 0.11±0.02(stat)+0.06−0.04(syst)±0.04(BPDG); this is much lower than the theoretical expectations (≈1) made under the assumption that K∗(1680) is a pure 13D1 state. The product branching fraction B(D0→[K∗2(1980)−→K−η]π+)=(2.2+1.7−1.9)×10−4 is determined. In addition, the πη′ contribution to the a0(980)± resonance shape is confirmed with 10.1σ statistical significance using the three-channel Flatté model. We also measure B(D0→K¯∗(892)0η)=(1.41+0.13−0.12)%. This is consistent with, and more precise than, the current world average (1.02±0.30)%, deviates with a significance of more than 3σ from the theoretical predictions of (0.51-0.92)%.