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Register a new userNonuniversality of indirect CP asymmetries in $D to pipi, KK$ decays
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Amol Dighe
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We point out that, if the direct CP asymmetries in the $D to pi^+ pi^-$ and $D to K^+ K^-$ decays are unequal, the indirect CP asymmetries as measured in these modes are necessarily unequal. This nonuniversality of indirect CP asymmetries can be significant with the right amount of new physics contributions, a scenario that may be fine-tuned, but is still viable. A model-independent fit to the current data allows different indirect CP asymmetries in the above two decays. This could even be contributing to the apparent tension between the difference CP asymmetries $Delta A_{rm CP}$ measured through the pion-tagged and muon-tagged data samples at the LHCb. This also implies that the measurements of $A_Gamma$ and $y_{rm CP}$ in the $pi^+ pi^-$ and $K^+ K^-$ decay modes can be different, and averaging over these two modes should be avoided. In any case, the complete analysis of CP violation measurements in the $D$ meson sector needs to take into account the possibility of different indirect CP asymmetries in the $pi^+pi^-$ and $K^+ K^-$ channels.
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A study of indirect CP violation in $D^0$ mesons through the determination of the parameter $A_Gamma$ is presented using a data sample of $pp$ collisions, corresponding to an integrated luminosity of 1.0 fb$^{-1}$, collected with the LHCb detector and recorded at the centre-of-mass energy of 7 TeV at the LHC. The parameter $A_Gamma$ is the asymmetry of the effective lifetimes measured in decays of $D^0$ and $bar{D}^0$ mesons to the CP eigenstates $K^-K^+$ and $pi^-pi^+$. Fits to the data sample yield $A_Gamma(KK)=(-0.35pm0.62pm0.12)times 10^{-3}$ and $A_Gamma(pipi)=(0.33pm1.06pm0.14)times 10^{-3}$, where the first uncertainties are statistical and the second systematic. The results represent the worlds best measurements of these quantities. They show no difference in $A_Gamma$ between the two final states and no indication of CP violation.
The CP violating asymmetries for Cabibbo suppressed charged D meson decays in the standard model are estimated in the factorized approximation, using the two-loop effective hamiltonian and a model for final state interactions previously tested for Cabibbo allowed D decays. No new parameters are added. The predictions are larger than expected and not too far from the experimental possibilities.
Time-dependent $CP$ asymmetries in the decay rates of the singly Cabibbo-suppressed decays $D^0rightarrow K^-K^+$ and $D^0rightarrow pi^-pi^+$ are measured in $pp$ collision data corresponding to an integrated luminosity of 3.0 fb$^{-1}$ collected by the LHCb experiment. The $D^0$ mesons are produced in semileptonic $b$-hadron decays, where the charge of the accompanying muon is used to determine the initial state as $D^0$ or $bar{D}^0$. The asymmetries in effective lifetimes between $D^0$ and $bar{D}^0$ decays, which are sensitive to indirect $CP$ violation, are determined to be begin{align*} A_{Gamma}(K^-K^+) = (-0.134 pm 0.077 ; {}^{+0.026}_{-0.034})% , A_{Gamma}(pi^-pi^+) = (-0.092pm 0.145 ; {}^{+0.025}_{-0.033})% , end{align*} where the first uncertainties are statistical and the second systematic. This result is in agreement with previous measurements and with the hypothesis of no indirect $CP$ violation in $D^0$ decays.
We report a measurement of the indirect CP-violating asymmetries ($A_{Gamma}$) between effective lifetimes of anticharm and charm mesons reconstructed in $D^0to K^+ K^-$ and $D^0to pi^+pi^-$ decays. We use the full data set of proton-antiproton collisions collected by the Collider Detector at Fermilab experiment and corresponding to $9.7$~fb$^{-1}$ of integrated luminosity. The strong-interaction decay $D^{*+}to D^0pi^+$ is used to identify the meson at production as $D^0$ or $overline{D}^0$. We statistically subtract $D^0$ and $overline{D}^0$ mesons originating from $b$-hadron decays and measure the yield asymmetry between anticharm and charm decays as a function of decay time. We measure $A_Gamma (K^+K^-) = (-0.19 pm 0.15 (stat) pm 0.04 (syst))%$ and $A_Gamma (pi^+pi^-)= (-0.01 pm 0.18 (stat) pm 0.03 (syst))%$. The results are consistent with the hypothesis of CP symmetry and their combination yields $A_Gamma = (-0.12 pm 0.12)%$.
We propose CP asymmetries based on triple product correlations in the decays sbottom_m -> top chargino_j with subsequent decays of top and chargino_j. For the subsequent chargino_j decay into a leptonic final state l^- u neutralino_1 we consider the three possible decay chains chargino_j -> l^- sneutrino -> l^- u neutralino_1, chargino_j -> slepton_n u -> l^- u neutralino_1 and chargino_j -> W^- neutralino_1 -> l^- u neutralino_1. We consider two classes of CP asymmetries. In the first class it must be possible to distinguish between different leptonic chargino_j decay chains, whereas in the second class this is not necessary. We consider also the 2-body decay chargino_j -> W^- neutralino_1, and we assume that the momentum of the W boson can be measured. Our framework is the minimal supersymmetric standard model with complex parameters. The proposed CP asymmetries are non-vanishing due to non-zero phases for the parameters mu and/or A_b. We present numerical results and estimate the observability of these CP asymmetries.
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