Measurement Of The Mixing Parameters Of Neutral Charm Mesons And Search For Indirect Cp Violation With D0 K0 S Decays At Lhcb

CERN Courier

Mixing and CP Violation in Charm Meson Decays

Mixing and CP violation (CPV) in the neutral D system were first discussed over thirty years ago but mixing was observed for the first time only very recently. Since then, these observations have been confirmed in other experiments and in other D° decay modes. Unlike the K, B and B{sub s} systems, for which mixing was observed years earlier, the short distance ([Delta]C = 2) amplitude contributing to mixing in the D system arises from box diagrams with down- rather than up-type quarks in the loops. The d and s components are GIM-suppressed, and the b component is suppressed by the small V{sub ub} CKM coupling. In the standard model (SM), therefore, long range, non-perturbative effects, a coherent sum over intermediate states accessible to both D° and {bar D}°, are the main contribution to mixing. These are hard to compute reliably, however. The phenomenon of mixing in neutral meson systems has now been observed in all flavours, but only in the past year in the D° system. The standard model anticipated that, for the charm sector, the mixing rate would be small, and also that CP violation, either in mixing or in direct decay, would be below the present levels of observability. It is hoped that further study of these phenomena might reveal signs of new physics. A review of recently available, experimental results is given.

Measurement of CP Violation Parameters in B Quark Decays to Charm Anticharm Down Quarks, Exclusive Decays at the BABAR Experiment

The BABAR experiment at SLAC provides an opportunity for measurement of CP violation in B decays. A measurement of time-dependent CP violating asymmetries using exclusive B meson decays where the b quark decays to c[bar c]d (including B[sup 0][yields] D*[sup+]D*[sup -] and B[sup 0][yields] D*[sup[+-]]D[sup[-+]] decays) is presented here. This is the first measurement of CP violation in a mode sensitive to the Unitarity Triangle parameter sin2[beta] outside of decays containing charmonium. It provides a comparison to measurements of sin2[beta] using b[yields] c[bar c]s, and permits an observation into potential new physics sources of CP violation, such as supersymmetry, via differences between these measurements and those of B[sup 0][yields] J/[psi] K[sub S][sup 0] as statistics of reconstructed neutral B decays to D[sup (*)+] D[sup (*)-] increase. The measured value of the time-dependent CP violating asymmetries are: S= 0.38[+-] 0.88(stat)[+-] 0.12(syst) and C= -0.30[+-] 0.50(stat)[+-] 0.13(syst) for B[sup 0][yields] D*[sup -] D[sup+]; S= -0.43[+-] 1.41(stat)[+-] 0.23(syst) and C= 0.53[+-] 0.74(stat)[+-] 0.15(syst) for B[sup 0][yields] D*[sup+] D[sup -]; and S= -0.05[+-] 0.45(stat)[+-] 0.05(syst) and C= 0.12[+-] 0.30(stat)[+-] 0.05(syst) for B[sup 0][yields] D*[sup -] D[sup+]; where S corresponds to CP violation in the interference of mixing and decay and C corresponds to CP violation in decay.