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Register a new userImplications of D^0-bar D^0 Mixing for New Physics
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We provide a comprehensive, up-to-date analysis of possible New Physics contributions to the mass difference $Delta M_D$ in $D^0$-${bar D}^0$ mixing. We consider the most general low energy effective Hamiltonian and include leading order QCD running of effective operators. We then explore an extensive list of possible New Physics models that can generate these operators, which we organize as including Extra Fermions, Extra Gauge Bosons, Extra Scalars, Extra Space Dimensions and Extra Symmetries. For each model we place restrictions on the allowed parameter space using the recent evidence for observation of $D$ meson mixing. In many scenarios, we find strong constraints that surpass those from other search techniques and provide an important test of flavor changing neutral currents in the up-quark sector. We also review the recent BaBar and Belle findings, and describe the current status of the Standard Model predictions of $D^0$-${bar D}^0$ mixing.
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Violation of charge conjugation-parity ($rm CP$) symmetry plays a major rule in the dominance of matter in our universe. A kind of $rm CP$ violation results from the asymmetry of the life time measured in $M^0$ and $bar M^0$, here $M$ is a heavy meson, decays to final states which is referred in the literature as $A_{Gamma}^f$. In this paper, we give an estimation of the upper bound on $|A_{Gamma}^f|$ for the Cabibbo Favored $D^0 rightarrow K^- pi^+$ decay process in different models. We show that in the standard model, $|A_{Gamma}^f| lesssimmathcal{O} (10^{-10})$. Recently a bound on $A_{Gamma}^f$ has been obtained: $(A^f_{Gamma})^{Exp.}= (1.6 pm 1)times 10^{-4}$. This result motivates further studies on $A_{Gamma}^f$ in beyond standard model physics. In the framework of two Higgs doublet model with generic Yukawa structure, we show that $|A_Gamma^{f}|lesssim mathcal{O} (10^{-7})$ which is several orders of magnitude smaller than the current experimental value. Finally, in the framework of left-right symmetric models in which the mixing between the left and the right gauge bosons is allowed and the left-right symmetry is not manifest at unification scale, we find that $A_{Gamma}^f$ can be as large as $|A_{Gamma}^f|lesssimmathcal{O} (10^{-5})$ which is one order of magnitude smaller than the experimentally measured value by LHCb collaborators.
We observe $D^0-bar{D}^0$ mixing in the decay $D^0rightarrow K^+pi^-$ using a data sample of integrated luminosity 976 fb$^{-1}$ collected with the Belle detector at the KEKB $e^+e^-$ asymmetric-energy collider. We measure the mixing parameters ${x}^2 = (0.09pm0.22)times 10^{-3}$ and $y = (4.6pm3.4)times 10^{-3}$ and the ratio of doubly Cabibbo-suppressed to Cabibbo-favored decay rates $R_D = (3.53pm0.13)times 10^{-3}$, where the uncertainties are statistical and systematic combined. Our measurement excludes the no-mixing hypothesis at the 5.1 standard deviation level.
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.
We derive a new QCD sum rule for $D(0^+)$ which has only the $Dpi$ continuum with a resonance in the hadron side, using the assumption similar to that has been successfully used in our previous work to the mass of $D_s(0^+)(2317)$. For the value of the pole mass $M_c=1.38 $ GeV as used in the $D_s(0^+)$ case we find that the mass of $D(0^+)$ derived from this sum rule is significantly lower than that derived from the sum rule with the pole approximation. Our result is in agreement with the experimental dada from Belle.
Recently, the standard model predictions for the $B$-meson hadronic decays, $bar{B}^0 to D^{(ast)+}K^-$ and $bar{B}^0_s to D^{(ast)+}_s pi^-$, have been updated based on the QCD factorization approach. This improvement sheds light on a novel puzzle in the $B$-meson hadronic decays: there are mild but universal tensions between data and the predicted branching ratios. Assuming the higher-order QCD corrections are not huge enough to solve the tension, we examine several new physics interpretations of this puzzle. We find that the tension can be partially explained by a left-handed $W^prime$ model, which can be compatible with other flavor observables and collider bounds.
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