Abstract
We report the first observation of the radiative charm decay D^{0}→ρ^{0}γ and the first search for CP violation in decays D^{0}→ρ^{0}γ, ϕγ, and K[over ¯]^{*0}(892)γ, using a data sample of 943 fb^{-1} collected with the Belle detector at the KEKB asymmetric-energy e^{+}e^{-} collider. The branching fraction is measured to be B(D^{0}→ρ^{0}γ)=(1.77±0.30±0.07)×10^{-5}, where the first uncertainty is statistical and the second is systematic. The obtained CP asymmetries A_{CP}(D^{0}→ρ^{0}γ)=+0.056±0.152±0.006, A_{CP}(D^{0}→ϕγ)=-0.094±0.066±0.001, and A_{CP}(D^{0}→K[over ¯]^{*0}γ)=-0.003±0.020±0.000 are consistent with no CP violation. We also present an improved measurement of the branching fractions B(D^{0}→ϕγ)=(2.76±0.19±0.10)×10^{-5} and B(D^{0}→K[over ¯]^{*0}γ)=(4.66±0.21±0.21)×10^{-4}.
Highlights
We report the first observation of the radiative charm decay D0 → ρ0 γ and the first search for CP
We present an improved measurement of the branching fractions B D0 → φγ = (2.76±0.19±0.10)×10−5 and B D0 → K ∗0 γ = (4.66±0.21±0.21)×10−4
The search for CP violation in radiative charm decays is complementary to the searches that have been exclusively performed in hadronic or leptonic decays
Summary
[B(D0 → f ) − B(D0 → f )]/[B(D0 → f ) + B(D0 → f )], and on the contributions from the forward-backward production asymmetry (AFB ) [23–25] and the asymmetry due to different reconstruction efficiencies for positively and negatively charged particles If one of the daughter photons is missed in the reconstruction, the final state mimics the signal decay. Such events are suppressed with a dedicated π 0 veto in the form of a neural network [26]. For the ρ0 and K ∗0 modes, we restrict the helicity angle range to −0.8 < cos θH < 0.4 to suppress backgrounds that peak at the edges of the distribution. In all three signal modes, the ‘other-D0 ’ background comprises all other decays wherein the D0 is reconstructed from the majority of daughter particles. In the K ∗0 mode, the yields (and Araw ) of certain backgrounds that contain a small number of events (one or two orders of magnitude less than signal) are fixed:. K ∗0 (1430)− π + , K ∗− π + , and the ‘other-D0 ’ background
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