Studies of radiative charm decays at Belle

摘要

We report a measurement of the branching fractions of the radiative decays D~0 → V_γ, where V = φ, K~(*0) or p~0. This is the first observation of the decay D~0 → p~0γ. We measure preliminary branching fractions B (D~- → φγ) = (2.76 ± 0.20 ± 0.08) × 10~(-5), B (D~0 → K~(*0)γ) = (4.66 ± 0.21 ± 0.18) × 10~(-4) and B (D~0 → p~0γ) = (1.77±0.30±0.08) × 10~(-5), where the first uncertainty is statistical and the second systematic. We also present the first measurement of CP asymmetry in these decays. The preliminary values are A_(cp) (D~0 → φγ) = -0.094 ± 0.066 ± 0.001, A_(cp) (D~0 → K~(*0)γ) = -0.003±0.020±0.000 and A_(cp) (D~0 → p~0γ) = 0.056± 0.151 ± 0.006. We also present the results of the search for the rare charm decay D~0 →γγ, resulting in an upper limit on the branching fraction Br(D~0 → γγ)< 8.5 × 10~(-7) at 90% confidence level, the most restrictive limit to date.