Year: 2015
Type: article
Abstract: The direct $CP$ asymmetry ${a}_{CP}^{\text{dir}}({D}^{0}\ensuremath{\rightarrow}{K}_{S}{K}_{S})$ involves exchange diagrams which are induced at tree level in the Standard Model. Since the corresponding topological amplitude ${E}_{KK}$ can be large, ${D}^{0}\ensuremath{\rightarrow}{K}_{S}{K}_{S}$ is a promising discovery channel for charm $CP$ violation. We estimate the penguin annihilation amplitude with a perturbative calculation and extract the exchange amplitude ${E}_{KK}$ from a global fit to $D$ branching ratios. Our results are further used to predict the size of mixing-induced $CP$ violation. We obtain $|{a}_{CP}^{\text{dir}}({D}^{0}\ensuremath{\rightarrow}{K}_{S}{K}_{S})|\ensuremath{\le}1.1%$ (95% C.L.). The same bound applies to the nonuniversal part of the phase between the $D\ensuremath{-}\overline{D}$ mixing and decay amplitudes. If future data exceed our predictions, this will point to new physics or an enhancement of the penguin annihilation amplitude by QCD dynamics. We briefly discuss the implications of these possibilities for other $CP$ asymmetries.
Authors: Ulrich Nierste, Stefan Schacht
Institution: Karlsruhe Institute of Technology
Language: Latvian
Subfield: Nuclear and High Energy Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2210315375