D+ → η(')l+νl semileptonic decays in light-cone sum rules

We calculate the D → η transition form factor in light-cone sum rules by taking improved current correlators to avoid the pollution from the twist-3 wave function. We get consistent results of the D⁺ → η^(')l⁺ν_l decays with the experimental data. By comparing the difference between the results of the branching ratios of D⁺ → η^(')l⁺ν_l from a two-pole parameterization model and from a BZ parameterization model, we find that the two-pole model and the BZ model are comparably believable. One way is supposed for the determination of the η-η' mixing angle from the dependence of the branching ratios of D⁺ → η^(')l⁺ν_l decays on the η-η' mixing angle.     

Event generators for η/η' rare decays into π+π-l+l- and e+e-μ+μ-

Study of the rare and forbidden decays of η/η' offers a sensitive probe to test fundamental symmetries of quantum chromodynamics and search for new physics beyond the Standard Model. To study the rare decays of η/η' to π⁺π^-e⁺e^-, π⁺π^-μ⁺μ^- and e⁺e^-μ⁺μ^- at the BESⅢ detector, we developed several event generators based on the vector meson dominant model with finite-width corrections and the pseudoscalar mesons mixing theory. The various distributions from event generators are in good agreement with the theoretical predictions, which indicates that the event generators work very well after implemention in the BESⅢ Monte Carlo simulation package. In the BESⅢ physics analysis, the performance of the event generators will be improved in accordance with the distributions of different variables of η/η' from data and the improvement on the theoretical calculations.     

Semileptonic decays Bc→(ηc,J/Ψ)lv in the perturbative QCD approach

In this paper we study the semileptonic decays of B_c^-→(η_c,J/Ψ)l^-v_l. We first evaluate the B_c→(η_c,J/Ψ) transition form factors F₀(q²), F₊(q²), V(q²) and A_0,1,2(q²) by employing the pQCD factorization approach, and then we calculate the branching ratios for all considered semileptonic decays. Based on the numerical results and the phenomenological analysis, we find that: (a) the pQCD predictions for the values of the B_c→η_c and B_c→J/Ψ transition form factors agree well with those obtained by using other methods; (b) the pQCD predictions for the branching ratios of the considered decays are Br(B_c^-→η_c e^-v_e(μ^-v_μ)=(4.41_-1.09^+1.22)×10^-3, Br(B_c^-→η_cτ^-v_τ) =(1.37_-0.34^+0.37)×10^-3, Br(B_c^-→J/Ψ e^-v_e(μ^-v_μ)) =(10.03_-1.18^+1.33)×10^-3, and Br(B_c^-→J/Ψτ^-v_τ) =(2.92_-0.34^+0.40)×10^-3; and (c) we also define and calculate two ratios of the branching ratios R_ηc and R_J/Ψ, which will be tested by LHCb and the forthcoming Super-B experiments.     

Radial excitation states of η and η' in the chiral quark model

A chiral quark model is applied to calculate the spectra of pseudoscalar mesons η and η'. By analyzing the obtained spectra, we find that the mesons η'(2¹S₀), η(4¹S₀), η'(3¹S₀) and η'(4¹S₀) are the possible candidates of η(1760), X(1835), X(2120) and X(2370). The strong decay widths of these pseudoscalars to all the possible two-body decay channels are calculated within the framework of the ³P₀ model. Although the total width of η'(2¹S₀) is compatible with the BES Collaboration's experimental value for η(1760), the partial decay width to ωω is too small, which is not consistent with the BES result. If X(1835) is interpreted as η(4¹S₀), the total decay width is compatible with the experimental data, and the main decay modes will be mπ a₀(980) and m π a₀(1450), which needs to be checked experimentally. The assignment of X(2120) and X(2370) to η'(3¹S₀) and η'(4¹S₀) is disfavored in the present calculation because of the incompatibility of the decay widths.     

Measuring D0-D0 mixing in D→f0(980) K and more

We investigate the D⁰-D⁰ mixing through the doubly Cabibbo suppressed (DCS) channel D0→f₀(980)K^*0 and its charge conjugate channel, in which the K^*0 meson is reconstructed in both K⁺π^－ and K_Sπ⁰ final state. Although the decay D⁰→f₀(980)K^* has a small branching ratio, the final state mesons are relatively easy to identify. The f₀(980) meson can be replaced by the S-wave π⁺π^－ state, or a longitudinally polarized vector meson ρ⁰. All mixing parameters, including the mass difference and decay width difference, can be extracted by studying the time-dependent decay width of these channels. We show that the method is valid in all regions for mixing parameters and it does not depend on the strong phase difference.     

Analysis of Λb→pK- and pπ- decays in a flavor changing Z' mode

In this paper, we calculate the branching ratios of Λ_b→pK^- and pπ^- decays in the avor changing Z' model. We nd that the branching ratios for these two decay modes are sensitive to the contributions of the Z' boson. For Λ_b→pK^- decay, if the left-handed couplings are equal to the right-handed couplings, the branching ratio of this decay could match up to the currently experimental data for ξ_s=0.01 and -52°<φ_s^L<132°, or ξ_s=0.004 and 0°<φ_s^L<84°; if only the left-handed couplings are considered, it could match up to the experimental data for ξ_s=0.01 and -10°φ_s^L<138°. And for Λ_b→pK^- decay, if the left-handed and right-handed couplings are equal, the branching ratio of Λ_b→pK^- decay may be consistent with the currently experimental data with ξ_d=0.05 and -135°φ_d^L<43°, if only the left-handed couplings are considered, it may be consistent with ξ_d=0.05 and -114°φ_d^L<8°.     

η production in proton-nucleus collisions near threshold

The η-meson production in proton-nucleus (pA) collisions near threshold is studied within a relativistic meson-exchange model. The primary production amplitude is presented in the distorted-wave impulse approximation for the nucleus with isospin 0 or 1 by assuming that N^*(1535) is excited via a meson exchange and then decays into η and nucleon pair(ηN). Taking ¹⁸O and ¹²C nuclei as examples, we evaluate the production cross sections as a function of the incident proton energy, and analyze the effects of nuclear medium and various meson-exchange contributions. Finally we discuss implications for further     

Properties of the coupling constants of J/ψ→VP decays

Based on the branching fractions of J/ψ→VP from different experiments, we investigate the properties of the coupling constants of J/ψ→VP decays using a model-dependent approach. We find that the octet coupling constant, g8, of strong interaction is about twice larger than that of the singlet coupling constant g₁; the electromag- netic breaking parameters g_Eⁱ are larger than the mass breaking parameters g_Mⁱ, moreover, the three parameters of the electromagnetic effect are about equal, but the three parameters of the mass effect are obviously different and their uncertainties are also large; and the phase angle between strong and electromagnetic interactions is in the range of 70°-80°. It deepens our understanding of the coupling constant of J/ψ→VP decays.     

Measurements of the γγ*→π0 and γγ*→ηc transition form factors at BABAR

We present measurements of the γγ*→π0 transition form factor for the momentum transfer range Q2=4-40 GeV2 and the γγ*→ηc transition form factor for the range Q2=2-50 GeV2.The current status of measurements of the meson-photon transition form factors for the η and η′ mesons is discussed.The results of the measurement of the ηc mass,total and two-photon widths are also presented.     

Uncertainty study of DS-(D-)→γlν (l=e,μ) decays determined by wave function

Wave function is important for determining decay constants f_DS^- and f_D^-. Using the 5 types of D meson wave functions in the heavy quark limit, we studied the uncertainties of radiative pure-leptonic decays of D_S^-(D^-) mesons. The branching ratios are (1.025390—1.706812) × 10^-5 and (0.953498—1.576725) × 10^-6 for D_S^- and D^- decays, respectively, which are sensitive to the type of wave function.