Zuo-Hong Li

Bio: Zuo-Hong Li is an academic researcher from Yantai University. The author has contributed to research in topics: Light cone & QCD sum rules. The author has an hindex of 6, co-authored 8 publications receiving 91 citations.

Semileptonic B(B(s), B(c)) decays in the light-cone QCD sum rules

Abstract: Semileptonic B(Bs, Bc) decays are investigated systematically in the light-cone QCD sum rules. Special emphasis is put on the LCSR calculation on weak form factors with an adequate chiral current correlator, which turns out to be particularly effective to control the pollution by higher twist components of spectator mesons. The result for each channel depends on the distribution amplitude of the the producing meson. The leading twist distribution amplitudes of the related heavy mesons and charmonium are worked out by a model approach in the reasonable way. A practical scenario is suggested to understand the behavior of weak form factors in the whole kinematically accessible ranges. The decay widths and branching ratios are estimated for several B(Bc) decay modes of current interest.

Semileptonic $B(B_s, B_c)$ decays in the light-cone QCD sum rules

Abstract: Semileptonic $B$($B_s, B_c$) decays are investigated systematically in the light-cone QCD sum rules. Special emphasis is put on the LCSR calculation on weak form factors with an adequate chiral current correlator, which turns out to be particularly effective to control the pollution by higher twist components of spectator mesons. The result for each channel depends on the distribution amplitude of the the producing meson. The leading twist distribution amplitudes of the related heavy mesons and charmonium are worked out by a model approach in the reasonable way. A practical scenario is suggested to understand the behavior of weak form factors in the whole kinematically accessible ranges. The decay widths and branching ratios are estimated for several $B$($B_c$) decay modes of current interest.

X(3872) and Other Possible Heavy Molecular States

Abstract: We perform a systematic study of the possible molecular states composed of a pair of heavy mesons such as $D\bar{D}$ , $D^{\ast}\bar{D}$ , $D^{\ast}\bar{D}^{\ast}$ in the framework of the meson exchange model. The exchanged mesons include the pseudoscalar, scalar and vector mesons. Through our investigation, we find the following results. (1) The structure X(3764) is not a molecular state. (2) There exists strong attraction in the range r<1 fm for the $D^{*}\bar{D}^{*}$ system with J=0,1. If future experiments confirm Z +(4051) as a loosely bound molecular state, its quantum number is probably J P =0+. Its partner state Φ **0 may be searched for in the π 0 χ c1 channel. (3) Vector meson exchange provides strong attraction in the $D^{\ast}\bar{D}$ channel together with pion exchange. A bound state solution may exist with a reasonable cutoff parameter Λ∼1.4 GeV. X(3872) may be accommodated as a molecular state dynamically although drawing a very definite conclusion needs further investigation. (4) The $B^{\ast}\bar{B}$ molecular state may exist.

Final state interactions in hadronic B decays

Abstract: There exist many experimental indications that final-state interactions (FSIs) may play a prominent role not only in charmful $B$ decays but also in charmless $B$ ones. We examine the final-state rescattering effects on the hadronic $B$ decay rates and their impact on direct CP violation. The color-suppressed neutral modes such as ${B}^{0}\ensuremath{\rightarrow}{D}^{0}{\ensuremath{\pi}}^{0},{\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0},{\ensuremath{\rho}}^{0}{\ensuremath{\pi}}^{0},{K}^{0}{\ensuremath{\pi}}^{0}$ can be substantially enhanced by long-distance rescattering effects. The direct CP-violating partial rate asymmetries in charmless $B$ decays to $\ensuremath{\pi}\ensuremath{\pi}/\ensuremath{\pi}K$ and $\ensuremath{\rho}\ensuremath{\pi}$ are significantly affected by final-state rescattering, and their signs are generally different from that predicted by the short-distance (SD) approach. For example, direct CP asymmetry in ${B}^{0}\ensuremath{\rightarrow}{\ensuremath{\rho}}^{0}{\ensuremath{\pi}}^{0}$ is increased to around 60% due to final-state rescattering effects whereas the short-distance picture gives about 1%. Evidence of direct CP violation in the decay ${\overline{B}}^{0}\ensuremath{\rightarrow}{K}^{\ensuremath{-}}{\ensuremath{\pi}}^{+}$ is now established, while the combined BABAR and Belle measurements of ${\overline{B}}^{0}\ensuremath{\rightarrow}{\ensuremath{\rho}}^{\ifmmode\pm\else\textpm\fi{}}{\ensuremath{\pi}}^{\ensuremath{\mp}}$ imply a $3.6\ensuremath{\sigma}$ direct CP asymmetry in the ${\ensuremath{\rho}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ mode. Our predictions for CP violation agree with experiment in both magnitude and sign, whereas the QCD factorization predictions (especially for ${\ensuremath{\rho}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$) seem to have some difficulty with the data. Direct CP violation in the decay ${B}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{0}$ is very small ($\ensuremath{\lesssim}1%$) in the standard model even after the inclusion of FSIs. Its measurement will provide a nice way to search for new physics as in the standard model QCD penguins cannot contribute (except by isospin violation). Current data on $\ensuremath{\pi}K$ modes seem to violate the isospin sum-rule relation, suggesting the presence of electroweak penguin contributions. We have also investigated whether a large transverse polarization in $B\ensuremath{\rightarrow}\ensuremath{\phi}{K}^{*}$ can arise from the final-state rescattering of ${D}^{(*)}{\overline{D}}_{s}^{(*)}$ into $\ensuremath{\phi}{K}^{*}$. While the longitudinal polarization fraction can be reduced significantly from short-distance predictions due to such FSI effects, no sizable perpendicular polarization is found owing mainly to the large cancellations occurring in the processes $\overline{B}\ensuremath{\rightarrow}{D}_{s}^{*}\overline{D}\ensuremath{\rightarrow}\ensuremath{\phi}{\overline{K}}^{*}$ and $\overline{B}\ensuremath{\rightarrow}{D}_{s}{\overline{D}}^{*}\ensuremath{\rightarrow}\ensuremath{\phi}{\overline{K}}^{*}$, and this can be understood as a consequence of CP and SU(3) [CPS] symmetry. To fully account for the polarization anomaly (especially the perpendicular polarization) observed in $B\ensuremath{\rightarrow}\ensuremath{\phi}{K}^{*}$, FSI from other states or other mechanism, e.g., the penguin-induced annihilation, may have to be invoked. Our conclusion is that the small value of the longitudinal polarization in $VV$ modes cannot be regarded as a clean signal for new physics.

LHCb anomaly and B physics in flavored Z ′ models with flavored Higgs doublets

Abstract: We study an extended Standard Model with a gauged ${\mathrm{U}(1)}^{\ensuremath{'}}$ flavor symmetry, motivated not only by the fermion mass hierarchy but also by the excesses in $B\ensuremath{\rightarrow}{K}^{(*)}ll$ reported by the LHCb collaborations. The ${\mathrm{U}(1)}^{\ensuremath{'}}$ charges are assigned to quarks and leptons in a flavor-dependent manner, and flavored Higgs doublets are also introduced in order to detail the Yukawa couplings at the renormalizable level. Then, the fermion mass hierarchy is realized by the vacuum alignment of the Higgs doublets. In this model, flavor-changing currents involving the gauge boson of ${\mathrm{U}(1)}^{\ensuremath{'}}$ and the scalars generated by the Higgs doublets are predicted and the observables in the $B\ensuremath{\rightarrow}{K}^{(*)}ll$ process possibly deviate from the Standard Model predictions. We study the possibility that these new flavor-changing interactions can explain the excesses in the $B\ensuremath{\rightarrow}{K}^{(*)}ll$ process, and we derive some predictions for the other flavor-violating processes based on the analysis. We specifically investigate the $\mathrm{\ensuremath{\Delta}}F=2$ processes and the other $B$ decays: e.g., $B\ensuremath{\rightarrow}{X}_{s}\ensuremath{\gamma}$ and $B\ensuremath{\rightarrow}{D}^{(*)}\ensuremath{\tau}\ensuremath{ u}$, where the deviations are reported by the Belle and BABAR collaborations.

Semileptonic B-c decays and charmonium distribution amplitude

Abstract: In this paper we study the semileptonic decays of the B-c meson in the light-cone sum rule (LCSR) approach. The result for each channel depends on the corresponding distribution amplitude (DA) of the final meson. For the case of B, decaying into a pseudoscalar meson, to twist-3 accuracy only the leading twist distribution amplitude is involved if we start from a chiral current. If we choose a suitable chiral current in the vector meson case, the main twist-3 contributions are also eliminated and we can consider the leading twist contribution only. The leading twist distribution amplitudes of the charmonium and other heavy mesons are given by a model approach in a reasonable way. Employing this charmonium distribution amplitude we find a cross section sigma-(e(+)e(-) -> J/Psi +eta(c)) similar or equal to 22.8 fb that is consistent with Belle and BaBar data. Based on this model, we calculate the form factors for various B-c decay modes in the corresponding regions. Extrapolating the form factors to the whole kinetic regions, we get the decay widths and branching ratios for various B, decay modes including their tau modes when they are kinematically accessible.