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Xue-Qing Hu

Publications and source records attributed to Xue-Qing Hu.

3 recordsLinked to original sources
arXiv2020

Study of $\bar{B}_s\to K^{(*)}\ell^+ \ell^-$ decays in the PQCD factorization approach with the lattice QCD input

In this paper, we studied systematically the semileptonic decays $\bar{B}_s \to K^{(*)} \ell^+ \ell^-$ with $l^-=(e^-,μ^-,τ^-)$ by using the perturbative QCD (PQCD) and the "PQCD+Lattice" factorization approach, respectively. We first evaluated all relevant form factors $F_i(q^2)$ in the low $q^2$ region using the PQCD approach, and we also take the available Lattice QCD results at the end point $q^2_{max}$ as additional inputs to improve the extrapolation of the form factors to the high $q^2$ region. We calculated the branching ratios and other twelve kinds of physical observables. From our studies, we find the following points: (a) for $ \bar{B}_s \to K l^+ l^-$ decays, the PQCD and "PQCD+Lattice" predictions for branching ratios (BRs) ${\cal B}(\bar{B}_s \to K l^+ l^-)$, the ratios of the BRs $R_K^{eμ}$ and $R_K^{μτ}$, and the longitudinal polarization asymmetry of the leptons $P_L$ agree well within errors; (b) the PQCD and "PQCD+Lattice" predictions for the CP averaged branching ratio ${\cal B}(\bar{B}_s \to K^* μ^+ μ^-)$ are $(3.17^{+0.95}_{-0.78})\times 10^{-8}$ and $(2.48^{+0.56}_{-0.50})\times 10^{-8}$ respectively, which agree well with the LHCb measured value $(2.9\pm 1.1) \times 10^{-8}$ and the light-cone sum rule (LCSR) prediction; (c) for the ratios $R_{K^\ast}^{eμ}$ and $R_{K^\ast}^{μτ}$, the PQCD and "PQCD+Lattice" predictions agree well with each other and have a small error less than $10\%$; (d) for the direct CP asymmetries ${\cal A}_{CP}$ of all considered decay modes, they are always very small as expected: less than $5\%$ in magnitude; and (e) for the angular observables $P_{1,2,3}$ and $P^\prime_{4,5,6,8}$ , our theoretical predictions for each kind of lepton are consistent within errors. We believe that above predictions could be tested by future LHCb and Belle-II experiments.

hep-ph↗
arXiv2020

Semileptonic decays $B/B_s \to (D^{(*)},D_s^{(*)}) l ν_l$ in the PQCD approach with the lattice QCD input

In this paper, we studied the semileptonic $B/B_s \to (D^{(*)},D_s^{(*)}) lν_l$ decays in the framework of the standard model (SM) , by employing the perturbative QCD (PQCD) factorization formalism combining with the lattice QCD inputs of the relevant transition form factors. We calculated the branching ratios ${\cal B}(B_{(s)} \to D_{(s)}^{(*)} l ν_l )$ with $l=(e,μ.τ)$ , the ratios of the branching ratios $R(D^{(*)})$ and $R(D_s^{(*)} )$ and other physical observables $P_τ(D_{(s)}^{(*)})$, $F_L(D^*_{(s)})$ and $A_{FB}(τ)$. The "PQCD+Lattice" predictions for ${\cal B}(B \to D^{(*)} lν_l)$ and $R(D^{(*)})$ do agree well with those currently available experimental measurements within the errors. For the ratios $R(D_s)$ and $R(D_s^*)$, the "PQCD+Lattice" predictions agree well with other known predictions. For both $P_τ(D^*)$ and $F_L(D^*)$, our theoretical predictions agree well with the measured values within errors. Our theoretical predictions about the considered semileptonic $B/B_s$ decays could be tested in the near future LHCb and the Belle II experiments.

hep-ph↗
arXiv2019

Semileptonic decays $B_c \to (η_c,J/ψ) l \barν_l $ in the "PQCD + Lattice" approach

In this paper, we studied the semileptonic decays $B_c^- \to (η_c, J/ψ) l ^- \barν_l$ by employing the PQCD factorization approach, using the newly defined distribution amplitudes of the $B_c$ meson and the new kind of parametrization for extrapolation of the form factors , and also taking into account the lattice QCD results about the relevant form factors at several points. We found the following main results: (a) the PQCD predictions for the branching ratios of $B_c \to (η_c,J/ψ) l \barν$ decays will become a little smaller by about $(5-16)\%$ when the lattice input are taken into account in the extrapolation of the relevant form factors; (b) the PQCD predictions for the ratio $R_{η_c, J/ψ}$ and the longitudinal polarization $P_τ$ are $R_{η_c}=0.34\pm 0.01 , R_{J/ψ}=0.28\pm 0.01$, $P_τ(η_c) = 0.37\pm 0.01$ and $P_τ(J/ψ) = -0.55 \pm 0.01$ ; and (c) after the inclusion of the lattice input the theoretical predictions changed slightly: $R_{η_c}=0.31\pm 0.01$, $ R_{ J/ψ}=0.27\pm 0.01$, $P_τ( η_c) = 0.36 \pm 0.01$ and $P_τ( J/ψ) = -0.53\pm 0.01$. The theoretical predictions for $R_{ J/ψ}$ agree with the measured one within errors, and other predictions could be tested in the near future LHCb experiments.

hep-ph↗