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Register a new userMixing and CP Violation in Decays of Charm Mesons
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Brian Meadows
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The phenomenon of mixing in neutral meson systems has now been observed in all flavours, but only in the past year in the D0 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.
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A study of mixing and indirect CP violation in D0 mesons through the determination of the parameters y_CP and A_Gamma is presented. The parameter y_CP is the deviation from unity of the ratio of effective lifetimes measured in D0 decays to the CP eigenstate K+K- with respect to decays to the Cabibbo favoured mode K-pi+. The result measured using data collected by LHCb in 2010, corresponding to an integrated luminosity of 29 pb^-1, is y_CP = (5.5+/-6.3_{stat}+/-4.1_{syst}) x 10^-3. The parameter A_Gamma is the asymmetry of effective lifetimes measured in decays of D0 and anti-D0 mesons to K+K-. The result is A_Gamma = (-5.9+/-5.9_{stat}+/-2.1_{syst}) x 10^-3. A data-driven technique is used to correct for lifetime-biasing effects.
Since the discovery of CP violation more than 5 decades ago, this phenomenon is still attracting a lot of interest. Among the many fascinating aspects of this subject, this review is dedicated to direct CP violation in non-leptonic decays. The advances within the last decade have been enormous, driven by the increasingly large samples of b- and c-hadron decays, and have led to very interesting results such as large CP asymmetries in charmless B decays and the observation of direct CP violation in the charm sector. We address the quest for understanding the origin of strong phases, the importance of final state interactions and the relation with CPT symmetry, and different approaches to measure direct CP violation in these decays. The main experimental results and their implications are then discussed.
We present a brief review of CPV and mixing measurements in the charm sector, with emphasys in results published or presented since the previous edition of the Physics in Collision Symposia.
We present a summary of recent results on CP violation and mixing in the charm quark sector based on a high statistics sample collected by photoproduction experiment FOCUS (E831 at Fermilab). We have measured the difference in lifetimes for the $D^0$ decays: $D^0 to K^-pi^+$ and $D^0 to K^-K^+$. This translates into a measurement of the $y_{CP}$ mixing parameter in the $d0d0$ system, under the assumptions that $K^-K^+$ is an equal mixture of CP odd and CP even eigenstates, and CP violation is negligible in the neutral charm meson system. We verified the latter assumption by searching for a CP violating asymmetry in the Cabibbo suppressed decay modes $D^+ to K^-K^+pi^+$, $D^0 to K^-K^+$ and $D^0 to pi^-pi^+$. We show preliminary results on a measurement of the branching ratio $Gamma(D^{*+}to pi^+ (K^+pi^-))/Gamma(D^{*+}to pi^+ (K^-pi^+))$.
Evidence from the babar, Belle and CDF experiments for the phenomenon of dzdzb oscillations is reviewed. A summary is made of the current understanding of the parameters defining the mixing of mass eigenstates that give rise to the oscillations. Results of searches for CP violation induced by mixing, are given, and estimates for the precision of measurements that can be expected in future experiments are made.
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