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Register a new user$Lambda_b to Lambda + D (bar{D}^0)$ decays and CP-violation
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Fayyazuddin
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It is shown that interference of the amplitudes for the decays $Lambda_b to Lambda D$ and $Lambda_b to Lambda bar{D}^0$ gives rise to CP-violation.
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Charm physics has played all along a central role in particle physics, however the level of attention on it has tremendously increased in the last years because of the observation of fast $D^0-bar{D}^0$ flavour oscillations and because of very recent observed hints of CP violation. While in the past these would have been unambiguously interpreted as signs of New Physics, the revisitation of theoretical expectations, prompted by the latest experimental measurements, makes the picture not clear. This brief review covers the current status of CP-violating measurements in the $D^0-bar{D}^0$ system, both on the experimental and theoretical side.
The $CP$ violation observables $S$ and $C$ in the decay channel $B^0 !rightarrow D^+ D^-$ are determined from a sample of proton-proton collisions at center-of-mass energies of 7 and 8 TeV, collected by the LHCb experiment and corresponding to an integrated luminosity of 3 fb$^{-1}$. The observable $S$ describes $CP$ violation in the interference between mixing and the decay amplitude, and $C$ parametrizes direct $CP$ violation in the decay. The following values are obtained from a flavor-tagged, decay-time-dependent analysis: begin{align*} S &= -0.54 , ^{+0.17}_{-0.16} , text{(stat)} pm 0.05 , text{(syst)},, ewline C &= phantom{-}0.26 , ^{+0.18}_{-0.17} , text{(stat)} pm 0.02 , text{(syst)},. end{align*} These values provide evidence for $CP$ violation at a significance level of 4.0 standard deviations. The phase shift due to higher-order Standard Model corrections is constrained to a small value of begin{align*} Deltaphi = -0.16,^{+0.19}_{-0.21},text{rad},. end{align*}
In this paper we investigate CP violation in charged decays of $D$ meson. Particularly, we study the direct CP asymmetry of the Cabibbo favored non-leptonic $D^+ rightarrow bar K^0 pi^+$ and the doubly Cabibbo-suppressed decay mode $D^+ rightarrow K^0 pi^+$ within standard model, two Higgs doublet model with generic Yukawa structure and left right symmetric models. In the standard model, we first derive the contributions from box and di-penguin diagrams contributing to their amplitudes which are relevant to the generation of the weak phases essential for non-vanishing direct CP violation. Then, we show that these phases are so tiny leading to a direct CP asymmetry of order $10^{-11}$ in both decay modes. Regarding the two Higgs doublet model with generic Yukawa structure and after taking into account all constraints on the parameter space of the model, we show that the enhanced direct CP asymmetries can be 6 and 7 orders of magnitudes larger than the standard model prediction for $D^+ rightarrow bar K^0 pi^+$ and $D^+ rightarrow K^0 pi^+$ respectively. Finally, within left right symmetric models, we find that sizable direct CP asymmetry of ${mathcal O } (10^{-3})$ can be obtained for the decay mode $D^+ rightarrow bar K^0 pi^+$ after respecting all relevant constraints.
The great progress made recently in the sector of Flavor Physics has enabled to establish CP violation in the B-meson decays. The unitarity triangle derived from the unitarity relation $V_{ub}^* V_{ud} + V_{cb}^* V_{cd} + V_{tb}^* V_{td} = 0$ has been measured very precisely. To further asses our understanding of CP violation, it would be useful to carry out similar measurement of other triangles. In this note, we investigate the triangle derived from the relation $V_{ub}^* V_{us} + V_{cb}^* V_{cs} + V_{tb}^* V_{ts} = 0$. Two angles of this triangle ($alpha_s$ and $beta_s$) could be measured very accurately at FCCee using the decays $B_s(overline{B_s})rightarrow D^pm_sK^mp$ and $B_s(overline{B_s})rightarrow J/psi phi$ respectively, as discussed elsewhere by us. This note concentrates on the measurement of the third angle $gamma_s$ using the modes $B^pm to overline{D^0}(D^0)K^pm$. We show that a direct measurement of the angle $gamma_s$ is possible with some specific $B^pm$ decays with an estimated resolution of the order of 1$^circ$.
In this paper we study the direct CP asymmetry of the doubly Cabibbo-suppressed decay mode $D^0 to K^+ pi^- $ within standard model and two Higgs doublet model with generic Yukawa structure. In the standard model we derive the corrections to the tree level amplitude, generated from the box and di-penguin diagrams, required for generating the weak CP violating phases. We show that these phases are so tiny leading to a direct CP asymmetry of order $10^{-9}$. Regarding the two Higgs doublet model with generic Yukawa structure we derive the Wilson coefficients relevant to $D^0 to K^+ pi^- $. After taking into account all constraints on the parameter space of the model we show that charged Higgs couplings to quarks can lead to a direct CP asymmetry of order $10^{-3}$ which is $6$ orders of magnitude larger than the standard model prediction.
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