arXiv subjects

Zhi-zhong Xing

Publications and source records attributed to Zhi-zhong Xing.

At least 217 records · Page 12Linked to original sources

arXiv2000

Neutrinos: How Do They Mix and Violate CP ?

We discuss a simple model of lepton mixing and CP violation based on the flavor democracy of charge leptons and the mass degeneracy of neutrinos. A nearly bi-maximal flavor mixing pattern, which is favored by current data on atmospheric and solar neutrino oscillations, emerges naturally from this model after explicit symmetry breaking. The rephasing-invariant strength of CP or T violation can be as large as one percent, leading to significant probability asymmetries between ν_μ\to ν_e and \barν_μ\to \barν_e (or ν_e \to ν_μ) transitions in the long-baseline neutrino experiments. The possible matter effects on CP- and T-violating asymmetries are also taken into account.

hep-ph↗

arXiv2000

A Novel Possibility to Determine the CP-violating Phase γand the B^0_s-\bar{B}^0_s Mixing Parameter y_s at the Υ(5S) Resonance

We show that a CP-violating phase can be model-independently determined from the time-independent measurement of coherent B^0_s\bar{B}^0_s decays into (D^{(*)\pm}_s K^{(*)\mp})(D^{(*)\pm}_s K^{(*)\mp}) states at the Υ(5S) resonance. This phase amounts to (-γ) within the standard model, where γis the well-known angle of the quark mixing unitarity triangle. It is also possible to determine or constrain the B^0_s-\bar{B}^0_s mixing parameter y_s from the same measurement.

hep-ph↗

arXiv2000

Neutrino Mixing and Maximal CP Violation

We propose a phenomenological model of lepton mixing and CP violation based on the flavor democracy of charge leptons and the mass degeneracy of neutrinos. A nearly bi-maximal flavor mixing pattern, which is favored by current data on atmospheric and solar neutrino oscillations, emerges naturally from this model after explicit symmetry breaking. The rephasing-invariant strength of CP or T violation can be as large as one percent, leading to significant probability asymmetries between ν_μ\to ν_e and \barν_μ\to \barν_e (or ν_e \to ν_μ) transitions in the long-baseline neutrino experiments. The possible matter effects on CP- and T-violating asymmetries are also taken into account.

hep-ph↗

arXiv2000

Mass and Flavor Mixing Schemes of Quarks and Leptons

We give an overview of recent progress in the study of fermion mass and flavor mixing phenomena. The hints exhibited by the quark and lepton mass spectra towards possible underlying flavor symmetries, from which realistic models of mass generation could be built, are emphasized. A variety of schemes of quark mass matrices at low and superhigh energy scales are described, and their consequences on flavor mixing and CP violation are discussed. Instructive patterns of lepton mass matrices, which can naturally lead to large flavor mixing angles, are explored to interpret current data on atmospheric and solar neutrino oscillations. We expect that B-meson factories and long-baseline neutrino experiments will soon shed more light on the dynamics of fermion masses, flavor mixing and CP violation.

hep-ph↗

arXiv1999

Bi-maximal Neutrino Mixing Pattern Reexamined

I propose a simple extension of the bi-maximal neutrino mixing pattern, allowing slight coupling between solar and atmospheric neutrino oscillations as well as large CP violation. The new scenario is compatible with either the vacuum oscillation solution or the large-angle MSW solution to the solar neutrino

hep-ph↗

arXiv1999

CP Violation in B_d \to D^+D^-, D^{+}D^-, D^+D^{-} and D^{+}D^{-} Decays

CP asymmetries in B_d \to D^+D^-, D^{*+}D^-, D^+D^{*-} and D^{*+}D^{*-} decays are investigated with the help of the factorization approximation and isospin relations. We find that the direct CP violation is governed only by the short-distance penguin mechanism, while the indirect CP asymmetries in B_d \to D^{\pm}D^{*\mp} transitions may be modified due to the final-state rescattering effect. An updated numerical analysis shows that the direct CP asymmetry in B^0_d vs \bar{B}^0_d \to D^+D^- decays can be as large as 3%. The CP-even and CP-odd contributions to the indirect CP asymmetry in B^0_d vs \bar{B}^0_d \to D^{*+}D^{*-} decays are found to have the rates 89% and 11%, respectively. Some comments on the possibilities to determine the weak phase βand to test the factorization hypothesis are also given.

hep-ph↗

arXiv1999

Maximal Neutrino Mixing and Maximal CP Violation

hep-ph↗

arXiv1999

New Time Distributions of D^0-\bar{D}^0 or B^0-\bar{B}^0 Mixing and CP Violation

The formulae for D^0-\bar{D}^0 or B^0-\bar{B}^0 mixing and CP violation at the τ-charm or B-meson factories are derived, for the case that only the decay-time distribution of one D or B meson is to be measured. In particular, we point out a new possibility to determine the D^0-\bar{D}^0 mixing rate in semileptonic D decays at the Ψ(4.14) resonance; and show that both direct and indirect CP asymmetries can be measured at the Υ(4S) resonance without ordering the decay times of two B_d mesons or measuring their difference.

hep-ph↗

arXiv1999

Large Mixing and CP Violation in Neutrino Oscillations

I introduce a simple phenomenological model of lepton flavor mixing and CP violation based on the flavor democracy of charged leptons and the mass degeneracy of neutrinos. The nearly bi-maximal mixing pattern, which can interpret current data on atmospheric and solar neutrino oscillations, emerges naturally from this model. The rephasing-invariant strength of CP or T violation amounts to about one percent and could be measured in the long-baseline neutrino experiments. The similarity and difference between lepton and quark flavor mixing phenomena are also discussed.

hep-ph↗

arXiv1999

CP Asymmetries in B_d \to D^{+}D^{-} and B_s \to D^{+}_s D^{-}_s Decays: P-wave Dilution, Penguin and Rescattering Effects

Determination of the CP-violating parameters \sin 2βand \sin 2β' is shown to be possible from B^0_d vs \bar{B}^0_d \to D^{*+}D^{*-} and B^0_s vs \bar{B}^0_s \to D^{*+}_sD^{*-}_s decays {\it without} doing the angular analysis. The P-wave dilution factors of these two asymmetries are found to be 0.89 and 0.90, respectively, using the factorization approximation and heavy quark symmetry. The penguin-induced corrections amount to about 2% and 3% in the corresponding B_d and B_s channels. Final-state rescattering effects could be handled by detecting the neutral modes B^0_d and \bar{B}^0_d \to D^{*0}\bar{D}^{*0}.

hep-ph↗

arXiv1999

The Light Quark Sector, CP Violation, and the Unitarity Triangle

In view of the observed strong hierarchy of quark masses, we propose a new description of flavor mixing which is particularly suited for models of quark mass matrices based on flavor symmetries. The necessary and sufficient conditions for CP violation are clarified. The emergence of CP violation is primarily linked to a large phase difference (near 90^{\circ}) in the light quark sector. The unitarity triangle is determined by the mass ratios of the light quarks. We conclude that the unitarity triangle should be close or identical to a rectangular triangle, and CP violation is maximal in this sense. Instructive predictions for flavor mixing angles and CP-violating parameters, which can directly be confronted with the forthcoming data from B-meson factories, are obtained from a specific texture of quark mass matrices.

hep-ph↗

arXiv1999

Nearly Degenerate Neutrino Masses and Nearly Decoupled Neutrino Oscillations

We introduce a simple flavor symmetry breaking scheme, in which charged lepton masses have a strong hierarchy and neutrino masses are almost degenerate. It is possible to obtain a natural suppression of lepton flavor mixing between the 1st and 3rd families as well as the approximate decoupling of atmospheric and solar neutrino oscillations with nearly bi-maximal mixing factors. The similarity and difference between lepton and quark flavor mixing schemes are briefly discussed.

hep-ph↗

arXiv1999

Flavor Symmetry, K^0-\bar{K}^0 Mixing and New Physics Effects on CP Violation in D^{\pm} and D^{\pm}_s Decays

Flavor symmetry and symmetry breaking, K^0-\bar{K}^0 mixing and possible effects of new physics on CP violation in weak decay modes D^{\pm} \to K_{S,L} + X^{\pm}, (K_{S,L} + π^0)_{K^*} + X^{\pm} (for X =π, ρ, a_1) and D^{\pm}_s \to K_{S,L} + X^{\pm}_s, (K_{S,L} +π^0)_{K^*} + X^{\pm}_s (for X_s = K, K^*) are analyzed. Relations between D^{\pm} and D^{\pm}_s decay branching ratios are obtained from the d \Leftrightarrow s subgroup of SU(3) and dominant symmetry-breaking mechanisms are investigated. A CP asymmetry of magnitude 3.3\times 10^{-3} is shown to result in the standard model from K^0-\bar{K}^0 mixing in the final-state. New physics affecting the doubly Cabibbo-suppressed channels might either cancel this asymmetry or enhance it up to the percent level. A comparison between the CP asymmetries in D^{\pm}_{(s)} \to K_{S} X^{\pm}_{(s)} and D^{\pm}_{(s)} \to K_L X^{\pm}_{(s)} can pin down effects of new physics.

hep-ph↗

arXiv1999

Opposite-sign Dilepton Asymmetry of Neutral B Decays: a Probe of New Physics from CPT or ΔB = ΔQ Violation

We show that new physics, either from CPT violation in B^0-\bar{B}^0 mixing or from ΔB = -ΔQ transitions, may lead to an opposite-sign dilepton asymmetry of neutral B-meson decays. Both effects have the same time-dependent behavior and therefore are in general indistinguishable from each other. We also clarify some ambiguity associated with the constraint on CPT violation in semileptonic decays of incoherent B^0 and \bar{B}^0 mesons.

hep-ph↗

arXiv1998

Large Leptonic Flavor Mixing and the Mass Spectrum of Leptons

Implications of a simple model for the mass generation of leptons are studied, in particular for the upcoming long-baseline neutrino experiments. The flavor mixing angles are large (nearly maximal). The probability for the long-baseline ν_μ\leftrightarrow ν_e oscillation is predicted to be about 1%.

hep-ph↗

arXiv1998

Measuring CP Violation and Testing Factorization in B_d \to D^\pmD^\mp and B_s \to D^\pm_sD^\mp_s Decays

We show that the CP-violating phases βand β' can respectively be determined from the time-dependent measurements of B_d \to D^*\pmD^\mp and B_s \to D^*\pm_sD^\mp_s decays, whose final states are non-CP eigenstates. The penguin contributions to the mixing-induced interference quantities are expected to be about 4% or smaller. We also point out two observables of O(1), which are pure functions of decay constants and form-factors, for a clean test of the factorization hypothesis in neutral-B decays into two heavy charmed mesons.

hep-ph↗

arXiv1998

A Determination of the Weak Phase γfrom Color-allowed B^{\pm}_u \to DK^{\pm} Decays

We show that it is possible to determine the weak phase γ\equiv \arg (- V^*_{ub} V_{ud} / V^*_{cb} V_{cd}) of the Cabibbo-Kobayashi-Maskawa flavor mixing matrix only from the measurement of the color-allowed B^{\pm}_u \to D K^{\pm} decay rates. The uncertainty of this method, arising mainly from the factorization approximation for two tree-level spectator quark transitions, may be well controlled.

hep-ph↗

arXiv1998

A Phenomenological Interpretation of Atmospheric and Solar Neutrino Oscillations

We give a phenomenological interpretation of atmospheric and solar neutrino oscillations by considering two scenarios for the neutrino mass spectrum: (a) m_1 \ll m_2 \ll m_3 and (b) m_1 \approx m_2 \approx m_3. A new parametrization of the flavor mixing matrix, which can naturally reflect the hierarchy of lepton masses in scenario (a) and the approximate decoupling of solar and atmospheric neutrino oscillations, is highlighted. For scenario (b) an ansatz starting with flavor democracy for charged leptons and mass degeneracy for neutrinos is proposed, and two different symmetry breaking possibilities with ``maximal calculability'' are discussed. Finally we point out that possible (\sin^2 2θ, Δm^2) parameter-space correlation should seriously be taken into account in future analyses of neutrino oscillations.

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