arXiv subjects
Publications and source records attributed to Zhi-zhong Xing.
In this talk, we first make some brief comments on the phase-convention dependence of the CP-violating parameter ε_B. A simple framework is then presented for analyzing new physics contributions to B^0-\bar{B}^0 mixing and their effects on the lepton CP asymmetry, a promising signal to be further searched for in the first-round experiments of B factories.
We make an analysis of the phase-convention dependence of the CP-violating parameter ε_B and give some comments on the reported CLEO and OPAL constraints on Reε_B. It is emphasized that ε_B has little advantage for the study of CP violation in the B^0_d-\bar{B}^0_d system.
In anticipation for intensive experimental effort on B physics, theorists have introduced many ingenious ways to measure properties of the unitarity triangle. We review some of these methods. We will be critical in the hope that, if there is any defect in them, it can be remedied either theoretically or experimentally.
We consider three possible scenarios of new physics in B^0_d-\bar{B}^0_d mixing and propose a simple framework for analyzing their effects. This framework allows us to study the CP asymmetry in semileptonic B_d decays ({\cal A}_{SL}) and those in nonleptonic transitions such as B_d \to J/ψK_S and B_d \to π^+π^-. Numerically we find that new physics may enhance the magnitude of {\cal A}_{SL} up to the percent level within the appropriate parameter space. So measurements of {\cal A}_{SL} and its correlation with other CP asymmetries will serve as a sensitive probe for new physics in B^0_d-\bar{B}^0_d mixing.
In many extensions of the standard model, new physics is possible to contribute significantly to B^0_s-\bar{B}^0_s mixing. We show that the effect of new physics, both its phase information and its magnitude, can be isolated from measurements of CP asymmetries in the semileptonic B_s transitions and in some nonleptonic B_s decays into hadronic CP eigenstates. We also find that the rates of CP-forbidden decays at the Υ(5S) resonance are not suppressed by the large B_s mass difference, thus they can be used to extract the CP-violating phase of new physics in either B^0_s-\bar{B}^0_s or K^0-\bar{K}^0 mixing.
Determination of the characteristic CP-violating quantity \sin (2β) should be the central goal of a B-meson factory in its first-round experiments. Except the gold-plated channels B_d\to ψK_S and ψK_L, three other types of B_d decays to CP eigenstates can also serve for the extraction of \sin (2β) in the standard model: (a) the CP-forbidden transitions (B_d\bar{B}_d)_{Υ(4S)} \to (X_c K_S) (X_c K_S) and $(X_c K_L) (X_c K_L), where X_c = ψ, ψ', η_c, etc; (b) the decay modes B_d\to D^{(*)+}D^{(*)-} and D^{(*)0}\bar{D}^{(*)0}, whose amplitudes have simple isospin relations; and (c) the decay modes B_d\to (f_{CP})_D + (π^0, ρ^0, a^0_1, etc), in which f_{CP} is a CP eigenstate (such as π^+π^-, K^+K^- or K_S π^0) arising from either D^0 or \bar{D}^0 in the neglect of D^0-\bar{D}^0 mixing. We carry out an analysis of the CP-violating signals existing in these typical processes, without loss of the possibility that new physics might significantly affect B^0_d-\bar{B}^0_d or K^0-\bar{K}^0 mixing. We also show that the magnitude of \sin (2β) can be well determined, in terms of only |V_{us}|, m_d/m_s and m_u/m_c, from a variety of quark mass ansatze.
In view of the discovery potential associated with the future experiments of high-luminosity fixed target facilities, B-meson factories and τ-charm factories, we highlight some typical signals of D^0-\bar{D}^0 mixing and CP violation which are likely to show up in neutral D-meson decays to the semileptonic final states, the hadronic CP eigenstates, the hadronic non-CP eigenstates and the CP-forbidden states. Both time-dependent and time-integrated measurements are discussed, and particular interest is paid to D^0/\bar{D}^0 \to K_{S,L}+π^0 and D^0/\bar{D}^0\to K^{\pm}π^{\mp} transitions.
We present an isospin analysis of the decay modes B\to D\bar{D}, D^*\bar{D}, D\bar{D}^* and D^*\bar{D}^*, which allows determination of the final-state interaction phases. As these transitions have branching ratios of the order 10^{-4} or larger, they could be useful in detecting the CP- violating phase ϕ_1 \equiv \arg (-V^*_{cb} V_{cd} V_{tb} V^*_{td} ) in the first-round experiments of a B-meson factory. The problem of penguin pollution may still be present. Once the Kobayashi-Maskawa matrix elements are known, it is possible to obtain the magnitudes and relative phases of hadronic matrix elements for B\to D^{(*)}\bar{D}^{(*)}. This will in turn lead to some information about the penguin pollution.
By use of the one-loop renormalization group equations and current experimental data, we study the off-diagonal asymmetries of the Cabibbo-Kobayashi-Maskawa (CKM) matrix at the GUT scale in the framework of the standard model as well as its two Higgs and supersymmetric extensions. It is concluded that the possibility of a symmetric CKM matrix at the GUT scale has almost been ruled out.
D^0-\bar{D}^0 mixing at the detectable level or significant CP violation in the charm system may strongly signify the existence of new physics. In view of the large discovery potential associated with the fixed target experiments, the B-meson factories and the τ-charm factories, we make a further study of the phenomenology of D^0-\bar{D}^0 mixing and CP violation in neutral $D$-meson decays. The generic formulas for the time-dependent and time-integrated decay rates of both coherent and incoherent D^0\bar{D}^0 events are derived, and their approximate expressions up to the second order of the mixing parameters x_D and y_D are presented. Explicitly we discuss D^0-\bar{D}^0 mixing and various CP-violating signals in neutral D decays to the semileptonic final states, the hadronic CP eigenstates, the hadronic non-CP eigenstates and the CP-forbidden states. A few non-trivial approaches to the separate determination of x_D and y_D and to the demonstration of direct and indirect CP asymmetries in the charm sector are suggested.
We propose a simple but realistic pattern of quark mass matrices at the string scale, which can be derived from orbifold models of superstring theory with no use of gauge symmetries. This pattern is left-right symmetric and preserves the structural parallelism between up and down quark sectors. Its phenomenological consequences on flavor mixing and $CP$ violation are confronted with current experiments at the weak scale by use of the renormalization-group equations in the framework of the minimal supersymmetric standard model. We find that good agreement is achievable without fine-tuning.
We stress that the observed pattern of flavor mixings can be partly interpreted by the quark mass hierarchy without the assumption of specific quark mass matrices. The quantitatively proper relations between the Kobayashi-Maskawa matrix elements and quark mass ratios, such as $$|V_{cb}| \approx |V_{ts}| \approx \sqrt{2} (\frac{m_s}{m_b} -\frac{m_c}{m_t}) [1 + 3 (\frac{m_s}{m_b} + \frac{m_c}{m_t} ) ],$$ are obtainable from a simple {\it Ansatz} of flavor permutation symmetry breaking at the weak scale. We prescribe the same {\it Ansatz} at the supersymmetric grand unified theory scale, and find that its all low-energy consequences on flavor mixings and $CP$ violation are in good agreement with current experimental data.
We calculate the time-dependent and time-integrated decay rates of $(D^0\bar{D}^0)\rightarrow (K^{\pm}π^{\mp})(l^{\pm}X^{\mp})$ at the $ψ(3.77)$ and $ψ(4.14)$ resonances. The possibilities to distinguish between the effects of $D^0-\bar{D}^0$ mixing and doubly Cabibbo suppressed decay (DCSD) are illustrated, and the signal of $CP$ violation induced by the interplay of mixing and DCSD is discussed. Ratios of the decay rates of $(D^0\bar{D}^0)\rightarrow (K^{\pm}π^{\mp})(K^{\pm}π^{\mp})$ to that of $(D^0\bar{D}^0)\rightarrow (K^+π^-)(K^-π^+)$ are also recalculated by accommodating $CP$ violation and final-state interactions.
$D^0-\bar{D}^0$ mixing leads to the mass and width differences in the mass eigenstates of $D^0$ and $\bar{D}^0$ mesons (measured by parameters $x^{~}_D$ and $y^{~}_D$ respectively), but their magnitudes cannot be reliably predicted by the standard model. We show that it is possible to separately determine $x^{~}_D$ and $y^{~}_D$ through {\it time-integrated} measurements of the dilepton events of coherent $D^0\bar{D}^0$ decays on the $ψ(4.14)$ resonance at a $τ$-charm factory.
The two-body mesonic $B$ decays induced only via a single $W$-exchange or annihilation quark diagram, such as $B^-_u\rightarrow D^{(*)-}_sK^{(*)0}$ and $\bar{B}^0_d\rightarrow D^{(*)+}_sK^{(*)-}$, are analyzed in the factorization approximation. We estimate the branching ratios for those transitions into two pseudoscalar mesons, and find them to be negligibly small. The significant effect of final-state rescattering is illustrated by taking $B^-_u\rightarrow D^-\bar{K}^0$ for example.
$D^0-\bar{D}^0$ mixing at a detectable level requires the presence of new physics and may lead to some observable effects in weak decays of $B$ mesons. We show that $CP$ violation induced by $D^0-\bar{D}^0$ mixing can manifest itself in the decay-rate asymmetry of $B^+_u\rightarrow D_{L(H)}l^+ν^{~}_l$ vs $B^-_u\rightarrow D_{L(H)}l^-\barν^{~}_l$. A rephasing-invariant generalization of the Gronau-Wyler approach is made to determine the weak phase shift in $B^{\pm}_u\rightarrow D_{L(H)}K^{\pm}$, which is only sensitive to the underlying new physics in $D^0-\bar{D}^0$ mixing. We also demonstrate the possible effect of $D^0-\bar{D}^0$ mixing on $CP$ violation in decay modes of the type $B_d\rightarrow D_{L(H)}+(π^0, ρ^0, {\rm etc})$. Finally the model of four quark families is taken as an example to illustrate how the new physics affects $D^0-\bar{D}^0$ mixing, $B^0_d-\bar{B}^0_d$ mixing and $CP$ asymmetries in the relevant $B$ decays.
Unitarity triangles and characteristic measurables of the $3\times 3$ Cabibbo-Kobayashi-Maskawa (CKM) matrix are discussed. Beyond the $3\times 3$ CKM scheme we make a rephasing-invariant generalization of the Gronau-Wyler-Dunietz approach to determine the weak phase shift in $B^{\pm}_u\rightarrow D K^{\pm}$ or $B^0_d\rightarrow D K^{*0}$ vs $\bar{B}^0_d\rightarrow D \bar{K}^{*0}$, which is only sensitive to the underlying new physics in $D^0-\bar{D}^0$ mixing. We also show that the weak angle $γ\equiv \arg (-V^*_{ub}V^*_{cd}V_{ud}V_{cb})$ is possible to be determined from the $CP$ asymmetries of some $B_d$ decays, even in a non-standard model with an extended quark sector. Brief comments are given on tests of unitarity of the $3\times 3$ CKM matrix.
In the context of the standard electroweak model, we emphasize that $B_d\rightarrow D^0_{CP}K_S$ ($D^0_{CP}$ denotes a $CP$ eigenstate of $D^0$ or $\bar{D}^0$) can compete with $B_d\rightarrow π^+π^-$ in studying $CP$ violation and probing the Cabibbo-Kobayashi-Maskawa unitarity triangle. We discuss the measurables of direct and indirect $CP$ asymmetries in $B^0_d$ vs $\bar{B}^0_d\rightarrow D^0_{CP}K_S$ under the circumstance of an asymmetric $B$-meson factory running on the $Υ(4S)$ resonance, and show that both the weak and strong phases are experimentally determinable even in the presence of unknown final-state interactions.