On the double penguin-like contributions to theB^0 - \bar B^0 mixing

We investigate double penguin-like diagrams for the \(B^0 - \bar B^0 \) mixing, a missing piece in the literature. We find that the short-distance part of these diagrams contributes ?5% and thus is unimportant in reconciling the value of poorly determined parameters of the standard model and most recent experimental information. We also point out the long-distance hadronic complications which leave the \(B^0 - \bar B^0 \) mixing issue to some extent open.     

B^0 - \bar B^0 mixing within and beyond the standard model

The standard model with three fermion families is found to be compatible with the Argus observation of a relatively large amount of \(B_{^d }^0 - \bar B_d^0 \) mixing provided that the top quark is rather heavy. From an analysis of the existing information on mixing angles, and of the constraints imposed by the kaon system, in particular by the ε parameter, we conclude that almost certainlym _t <45 GeV and probablym _t >90 GeV. In view of the Argus result the standard model unambiguously leads to the prediction of a nearly maximal amount of \(B_{^s }^0 - \bar B_s^0 \) mixing. Apart from the rather obvious case of a fourth family of quarks, most “minimal” extensions of the standard model preserve the prediction of a large \(B_{^s }^0 - \bar B_s^0 \) mixing. We discuss \(B^0 - \bar B^0 \) mixing in minimal supersymmetric models compatible with the UA1 lower bounds on gluino and squark masses. Contributions from charged Higgs exchange in the box diagrams are also discussed. While supersymmetry (although marginally) and charged Higgses can lead to an appreciable enhancement of \(B^0 - \bar B^0 \) mixing, minimal left-right symmetric models actually predict a modest suppression of the effect with respect to the standard model.     

B^0 - \bar B^0 mixing in a supersymmetric model without at-quark

A model based on a low energySU(3)_c×SU(2)₁×SU(2)₂×U(1) _H gauge group is considered. Theb-quark couples mainly to thec-quark via a new heavyW-boson and thet-quark is omitted altogether. The model is shown to be compatible with low energy charged current data. \(B_d^0 - \bar B_d^0 \) mixing occurs through the exchange of the heavyW-boson and through gluino exchange in the supersymmetric version of the model. The calculated mixing is much smaller in both cases than the observed effect and the model is, therefore, ruled out.     

Constraints on the squark mass matrix from CP-violation and SUSY predictions for theB^0 - \bar B^0 systems

The parametersc andA of the squark mass matrix, which control flavour violation and left-right maxing respectively, are constrained by fitting ∈ and ∈′. The predictions for mixing and CP-violation in the \(B^0 - \bar B^0 \) system are calculated and then compared with both the predictions of the standard model and the available experimental data.     

CP, T and/or CPT violations in the K^0 - \overline K^0 system

The possible violation of the CP, T and/or CPT symmetries in the system is studied from a phenomenological point of view. With this aim, we first introduce parameters which represent the violation of these symmetries in the mixing parameters and decay amplitudes in a convenient and well-defined way and, treating these parameters as small, derive formulas which relate them to the experimentally measured quantities. We then perform numerical analyses, with the aid of the Bell–Steinberger relation, to derive constraints on these symmetry-violating parameters, firstly paying particular attention to the results reported by the KTeV Collaboration and the NA48 Collaboration, and then with the results reported by the CPLEAR Collaboration as well taken into account. A case study, in which either CPT symmetry orT symmetry is assumed, is also carried out. It is demonstrated that the CP andT symmetries are violated definitively at the level of in decays and presumably at the level of in the mixing, and that the Bell–Steinberger relation helps us to establish that CP andT violations are definitively present in mixing and to testCPT symmetry to a level of . Received: 14 February 2000 / Revised version: 24 April 2000 / Published online: 8 September 2000     

Investigation of inclusive CP asymmetries in \rm B^0 decays

A search for CP violating effects in the mixing of neutral B mesons is performed using a sample of 4.1 million hadronic Z decays collected with the ALEPH detector from 1991 to 1995. By studying time-dependent asymmetries in flavour-tagged samples of semileptonic and fully inclusive b-hadron decays, two measurements of the semileptonic asymmetry are extracted. No evidence for CP violation is observed, and the combined value is obtained. Received: 26 July 2000 / Published online: 8 June 2001     

Mixing and CP violation: fromB^0 - \overline {B^0 } to T^0 - \overline {T^0 }

We extend from \(B^0 - \overline {B^0 } to T^0 - \overline {T^0 } \) the study of neutral pseudoscalar mesons with respect to mixing and CP violation. The possibility of a quite large top quark mass necessitates a more careful computation of the box diagram amplitude. Our result is that, while in \(B^0 - \overline {B^0 } \) systems CP violation is expected to be very small (～10^?6) and mixing quite large (10–20% or more), precisely the opposite occurs for \( T^0 - \overline {T^0 } \) . In particular, CP violation in the \( T_u^0 - \overline {T_u^0 } \) system could be of the same order of magnitude as in the \(K^0 - \overline {K^0 } \) system (～10^?3) while the mixing is totally negligible.     

K^0 - \bar K^0 mixing and the chiral-bag model

TheB-parameter is determined by the chiralbag model calculation of the amplitude. This is correlated with theK⁺⁰ decay amplitude. The theoretical magnitude ofB-parameter depends on the final state interaction effects inK2 decays. Without the final state interaction correction one findsB(µ _B ² )0.37, with the correction includedB(µ _B ² )0.9. Similar connection between theoretical prediction of theK⁺⁰ decay amplitude and calculated value ofB parameter seems to exist in other approaches too.     

Improving bounds on flavor changing vertices in the two Higgs doublet model from B^0-\bar{B}^0 mixing

We find some constraints on the flavor changing vertices of the two Higgs doublet model, from the measurement. Although bounds from this observable have already been considered, this paper takes into account the role of a new operator not included previously, as well as the vertices , and . Using the Cheng–Sher parametrization, we find that for a relatively light charged Higgs boson (200–300 GeV), we obtain , while the parameter could have values up to about 50. In addition, we use bounds for and obtained from at next to leading order, and study the case where the only vanishing vertex factors are the ones involving quarks from the first family. We obtain that is not sensitive to the change of the parameter , while .     

Effects of final state interactions in B^ + \to D_S^ + \bar K^0 decay

We investigate the effects of final state interactions (FSI) contributions in the nonleptonic two body $B^ + \to D_S^ + \bar K^0$ decay, however the hadronic decay of $B^ + \to D_S^ + \bar K^0$ is analyzed by using “QCD factorization” (QCDF) method and final state interaction (FSI). First, the $B^ + \to D_S^ + \bar K^0$ decay is calculated via QCDF method and only the annihilation graphs exist in that method. Hence, the FSI must be seriously considered to solve the $B^ + \to D_S^ + \bar K^0$ decay and the D ⁰π⁺(D ⁰*ρ⁺), D ⁺π⁰(D ⁺*ρ⁰) and D ⁺η _c (D ⁺*J/ψ) via the exchange of K ^+(*), K ^0(*) and D _s ^+(*) mesones are chosen for the intermediate states. To estimate the intermediate states amplitudes, the QCDF method is again used. These amplitudes are used in the absorptive part of the diagrams. The experimental branching ratio of $B^ + \to D_S^ + \bar K^0$ decay is less than 8 × 10^?4 and the predicted branching ratio is 0.23 × 10^?9 in the absence of FSI effects and it becomes 6.74 × 10^?4 when FSI contributions are taken into account.     

CP asymmetries in decays of the D^{0}-\bar{D}^{0} system revisited

CP violation in neutral D meson decays to the CP eigenstates and non-CP eigenstates is studied systematically within the framework of the Cabibbo-Kobayashi-Maskawa model. The nonleptonic two-body decay processes and the decay processes with semileptonic tagging are discussed in detail and the upper bounds of the direct and indirect CP violation in these decay processes are obtained. A method to measure the mixing parameter [(e)\tilde]\tilde{\epsilon} and to separate the direct and indirect CP violation in the decay processes with semileptonic tagging are also discussed.     

CP nonconservation ine^ + e^ - \to t\bar tg

CP violation effects in $e^ + e^ - \to t\bar tg$ are examined. CP-odd,T _N -odd andT _N -even observables can both be used to extract information on the real and imaginary parts of Feynman amplitudes. The two Higgs doublet model with CP violating phase from neutral Higgs exchange is used to illustrate possible effects. In this particular model the expected luminosity of the future colliders seems to fall short by about one order of magnitude to detect such asymmetries.