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.     

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.     

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.     

Mixings and CP violations of theB^0 - \bar B^0 system in the four-generation model

We study the mixings and CP violations in the \(B^0 - \bar B^0 \) system together with the \(K^0 - \bar K^0 \) one in the four-generation model, taking into account the ARGUS data for the \(B_d^0 - \bar B_d^0 \) mixing. We take typical six cases of the mixing hierarchy and search for the allowed regions of three phases in the 4×4KM matrix. The CP violating parameter ? _K in the \(K^0 - \bar K^0 \) system gives a severe constraint for the phases, and the smaller mixing than that in the three-generation model is predicted for the \(B_s^0 - \bar B_s^0 \) system. The asymmetry parameters for the two-body non-leptonic decays of theB ⁰ and \(\bar B^0 \) mesons are also predicted.     

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 .     

Two-particle correlations and B^0\overline{B}^0 mixing

We study the EPR correlation implied by the entangled wavefunction of the pair created by the resonance. The analysis uses the basis provided by the mass eigenstates rather than the flavour states . Data on the inclusive dilepton charge ratio are close to the expectation of quantum mechanics, but nearly 8 standard deviations away from that of complete decoherence. Our results are compared with those obtained in the basis. Received: 24 November 1997 / Published online: 10 March 1998     

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.     

QCD Calculation ofK^0 - \bar K^0 mixing from three-point function sum rules

We calculate theB parameter for \(K^0 - \bar K^0 \) mixing in the framework of QCD sum rules for a three-point function involving pseudoscalar currents, and contrast our results with other calculations. We findB=0.5±0.1±0.2, where the first error reflects uncertainties in the various QCD parameters and the second one is an estimate of uncalculated three-loop radiative and higher order quark mass corrections.     

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.     

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.     

The standard model process e^ + e^ - \to \nu \bar \nu b\bar b and its Higgs signal at LEP II

We present and study the results for the standard model process $e^ + e^ - \to \nu \bar \nu b\bar b$ at c.m. energies 150 ≤ √s(GeV) ≤ 240 and for Higgs boson masses 60 GeV ≤ m _H ≤ 110 GeV, obtained from all tree-level diagrams and including the most important radiative corrections. The matrix elements have been calculated by the ‘spinor bracket’ method without neglecting masses, which is presented in detail. The √s-dependence and the interference properties of the Higgs boson contributions and of various coherent background contributions to the total cross section are examined and compared. The important differential distributions for the Higgs boson and the background components are studied, providing information useful for choosing cuts in Higgs searches. We also examine the effect of a minimal set of cuts and evaluate the importance of the WW fusion for detecting a higher mass Higgs boson at LEP II.