Measurement of branching fractions and search for CP violation in D ⁰ → π ⁺ π ⁻ η, D ⁰ → K ⁺ K ⁻ η, and D ⁰ → ϕη at Belle

We measure the branching fractions and CP asymmetries for the singly Cabibbo-suppressed decays D⁰ → π⁺π⁻η, D⁰ → K⁺K⁻η, and D⁰ → ϕη, using 980 fb⁻¹ of data from the Belle experiment at the KEKB e⁺e⁻ collider. We obtainB(D0→π+π−η)=[1.22±0.02(stat)±0.02(syst)±0.03(Bref)]×10−3,B(D0→K+K−η)=[1.80−0.06+0.07(stat)±0.04(syst)±0.05(Bref)]×10−4,B(D0→ϕη)=[1.84±0.09(stat)±0.06(syst)±0.05(Bref)]×10−4, where the third uncertainty (B_ref) is from the uncertainty in the branching fraction of the reference mode D⁰ → K⁻π⁺η. The color-suppressed decay D⁰ → ϕη is observed for the first time, with very high significance. The results for the CP asymmetries areACP(D0π+π−η)=[0.9±1.2(stat)±0.5(syst)]%,ACP(D0→K+K−η)=[−1.4±3.3(stat)±1.1(syst)]%,ACP(D0→ϕη)=[−1.9±4.4(stat)±0.6(syst)]%. The results for D⁰ → π⁺π⁻η are a significant improvement over previous results. The branching fraction and A_CP results for D⁰ → K⁺K⁻η, and the ACP result for D⁰ → ϕη, are the first such measurements. No evidence for CP violation is found in any of these decays. [Figure not available: see fulltext.]