Evidence for CP violation in the decay D+ → K(S)(0)π+

First Measurement of the B^{+}→π^{+}π^{0}π^{0} Branching Fraction and CP Asymmetry

We study B^{+}→π^{+}π^{0}π^{0} using 711  fb^{-1} of data collected at the ϒ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e^{+}e^{-} collider. We measure an inclusive branching fraction of (19.0±1.5±1.4)×10^{-6} and an inclusive CP asymmetry of (9.2±6.8±0.7)%, where the first uncertainties are statistical and the second are systematic, and a B^{+}→ρ(770)^{+}π^{0} branching fraction of (11.2±1.1±0.9_{-1.6}^{+0.8})×10^{-6}, where the third uncertainty is due to possible interference with B^{+}→ρ(1450)^{+}π^{0}. We present the first observation of a structure around 1  GeV/c^{2} in the π^{0}π^{0} mass spectrum, with a significance of 6.4σ, and measure a branching fraction to be (6.9±0.9±0.6)×10^{-6}. We also report a measurement of local CP asymmetry in this structure.

Recent Measurements of Decay Asymmetry Parameter and CP Asymmetry for Charmed Baryon Decays at Belle

We review the recent results from the Belle experiment on the measurements of branching fractions and decay asymmetry parameters (α) for the hadronic weak decays of charmed baryons, including Λc+→B+P: Λc+→(Λ,Σ0)h+ (h=π,K) and Λc+→Σ+(π0,η,η′); Ξc0→B+P: Ξc0→Ξ−π+; Ξc0→B+V: Ξc0→ΛK¯*0, Ξc0→Σ0K¯*0, and Ξc0→Σ+K*−. In addition, we present an overview of the searches for CP violation via the α-induced CP asymmetry for Λc+→(Λ,Σ0)h+ and Ξc0→Ξ−π+. Finally, we discuss the promising decay modes of Ωc0 which can be measured in the near future and are indispensable in searching for CP violation in the charm sector.

No-Go Theorem for Nonstandard Explanations of the τ→K_{S}πν_{τ} CP Asymmetry

The CP asymmetry in τ→K_{S}πν_{τ}, as measured by the BABAR collaboration, differs from the standard model prediction by 2.8σ. Most nonstandard interactions do not allow for the required strong phase needed to produce a nonvanishing CP asymmetry, leaving only new tensor interactions as a possible mechanism. We demonstrate that, contrary to previous assumptions in the literature, the crucial interference between vector and tensor phases is suppressed by at least 2 orders of magnitude due to Watson's final-state-interaction theorem. Furthermore, we find that the strength of the relevant CP-violating tensor interaction is strongly constrained by bounds from the neutron electric dipole moment and D-D[over ¯] mixing. These observations together imply that it is extremely difficult to explain the current τ→K_{S}πν_{τ} measurement in terms of physics beyond the standard model originating in the ultraviolet.

CP Asymmetries in Charm Decays into Neutral Kaons

We find a new CP-violation effect in charm decays into neutral kaons, which results from the interference between two tree (Cabibbo-favored and doubly Cabibbo-suppressed) amplitudes with the mixing of final-state mesons. This effect, estimated to be of an order of 10^{-3}, is much larger than the direct CP asymmetries in these decays, but missed in the literature. It can be revealed by measuring the difference of the time-dependent CP asymmetries in the D^{+}→π^{+}K_{S}^{0} and D_{s}^{+}→K^{+}K_{S}^{0} modes, which are accessible at the LHCb and Belle II experiments. If confirmed, the new effect has to be taken into account, as the above direct CP asymmetries are used to search for new physics.

CP violation in the B system

The phenomenon of CP violation is crucial to understand the asymmetry between matter and antimatter that exists in the Universe. Dramatic experimental progress has been made, in particular in measurements of the behaviour of particles containing the b quark, where CP violation effects are predicted by the Kobayashi-Maskawa mechanism that is embedded in the standard model. The status of these measurements and future prospects for an understanding of CP violation beyond the standard model are reviewed.