arXiv subjects

X. -H. Guo

Publications and source records attributed to X. -H. Guo.

At least 19 recordsLinked to original sources

arXiv2016

Calculation of 1/m^{2}_{b} corrections to Λ_b\rightarrowΛ_c decay widths in the Bethe-Salpeter equation approach

The matrix element of the weak transition Λ_b\rightarrowΛ_c can be expressed in terms of six form factors. Λ_Q(Q = b;c) can be regarded as composed of a heavy quark Q(Q = b;c) and a diquark which is made up of the remaining two light quarks. In this picture, we express these six form factors in terms of Bethe-Salpeter wave functions to second order in the 1/m_Q expansion. With the kernel containing both the scalar confinement and the one-gluon-exchange terms we calculate the form factors and the decay widths of the semileptonic decay Λ_b\rightarrowΛ_clv as well as nonleptonic decays Λ_b\rightarrowΛ_cP(V) numerically. We also add QCD corrections since they are comparable with 1/m_Q corrections.

hep-ph↗

arXiv2015

Study of $Λ_b\rightarrow~ Λl^+l^-$ and $Λ_b\rightarrow p l \barν$ decays in the Bethe-Salpeter equation approach

In our previous work, based on the $SU(6)$ spin-flavor wave function, we regard $Λ$ and $p$ as composed of different quark-diquark configurations and established the Bethe-Salpeter (BS) equations of configurations for quark and scalar diquark. In our present work, we apply this model to calculate the form factors of the semileptonic transitions $Λ_b\rightarrowΛl^+l^-$ $(l=μ,e,τ)$ and $Λ_b\rightarrow p l\barν$ within the Standard Model (SM). The decay $Λ_b\rightarrowΛμ^+μ^-$ is especially interesting since it has been measured in CDF and LHCb Collaborations and this rare decay is very sensitive to new physics effects. The decay $Λ_b\rightarrow p l\barν$ is a promising mode for the measurement of the Cabibbo-Kobayashi-Maskawa matrix element $|V_{ub}|$ at the Large Hadron Collider. In our calculations, depending on the ranges of the parameters in the model including the diquark mass and the interaction strength between the quark and the diquark in the kernel of the BS equation, we find that the branching ratio of $Λ_b\rightarrowΛμ^+μ^-$ in our model is consistent with the experimental data and the current experimental results from LHCb agree with the differential branching ratio of $Λ_b\rightarrowΛμ^+μ^-$ from our calculation except at the lager momentum transfer region. This indicates that there is still room for possible new physics effects. We also give comparisions of the total branching ratios of $Λ_b\rightarrowΛl^+l^-$ and $Λ_b\rightarrow p l\barν$ with those given by other phenomenological methods.

hep-ph↗

arXiv2013

$QQ^{\prime} \bar u \bar d$ bound state in the Bethe-Salpeter equation approach

In the heavy quark limit, we establish the Bethe-Salpeter equations for the ground state $QQ^{\prime} \bar u \bar d$ containing one heavy diquark $QQ^{\prime}$ ($Q, Q^{\prime}=b$ or $c$) and one light antidiquark $\bar u \bar d$. We solve the Bethe-Salpeter equations numerically in the covariant instantaneous approximations with the kernels containing a scalar confinement term and a one-gluon-exchange term. Numerical solutions for the Bethe-Salpeter wave functions are presented. The results show that the masses of $bb \bar u \bar d$, $bc \bar u \bar d$, and $cc \bar u \bar d$ bound states lie below the threshold of $\bar{B}^{*0}\,B^-$ or $B^0\,{B^*}^-$, $B^-D^+$ or $\bar{B}^{0} D^0$, and $D^+\,{D^*}^0$ or ${D^*}^+\,D^0$ mesons, respectively. The ground states $QQ^{\prime} \bar u \bar d$ may exist and we expect the forthcoming experimental data to confirm them.

hep-ph↗

arXiv2013

Calculation of 1/m^{2}_{b} corrections to <Λ_{b}(v,s)|\bar{b}γ^λγ_{5}b|Λ_{b}(v,s)> for polarized Λ_{b} in the Bethe-Salpeter equation approach

The heavy baryon Λ_{Q} (Q=b or c) can be regarded as composed of a heavy quark and a scalar light diquark which has good spin and isospin quantum numbers. In this picture we establish the Bethe-Salpeter (BS) equation for Λ_{Q} to second order in the 1/m_{Q} expansion. With the kernel containing both the scalar confinement and the one-gluon-exchange terms we solve the BS equation numerically. The value of the spin-dependant form factor for the matrix element <Λ_{b}{(v,s)}|\bar{b}γ^λγ_{5}b|Λ_{b}(v,s)>, ε_{b}, which is non-zero at order 1/m^{2}_{b}, is obtained numerically from our model.

hep-ph↗

arXiv2011

Bethe-Salpeter equation for doubly heavy baryons in the covariant instantaneous approximation

In the heavy quark limit, a doubly heavy baryon is regarded as composed of a heavy diquark and a light quark. We establish the Bethe-Salpeter (BS) equations for the heavy diquarks and the doubly heavy baryons, respectively, to leading order in a $1/m_{Q}$ expansion. The BS equations are solved numerically under the covariant instantaneous approximation with the kernels containing scalar confinement and one-gluon-exchange terms. The masses for the heavy diquarks and the doubly heavy baryons are obtained and the non-leptonic decay widths for the doubly heavy baryons emitting a pseudo-scalar meson are calculated within the model.

hep-ph↗

arXiv2009

Vacuum fluctuation effects on hyperonic neutron star matter

The vacuum fluctuation (VF) effects on the properties of the hyperonic neutron star matter are investigated in the framework of the relativistic mean field (RMF) theory. The VF corrections result in the density dependence of in-medium baryon and meson masses. We compare our results obtained by adopting three kinds of meson-hyperon couplings. The introduction of both hyperons and VF corrections soften the equation of state (EoS) for the hyperonic neutron star matter and hence reduce hyperonic neutron star masses. The presence of the $δ$ field enlarges the masses and radii of hyperonic neutron stars. Taking into account the uncertainty of meson-hyperon couplings, the obtained maximum masses of hyperonic neutron stars are in the range of $1.33M_{\odot}\sim1.55M_{\odot}$.

hep-ph↗

arXiv2009

Vacuum fluctuation effects on asymmetric nuclear matter

The vacuum fluctuation (VF) effects on asymmetric nuclear matter are investigated. Masses of nucleons and mesons are modified in the nuclear medium by calculating the loop-diagram corrections and the density dependence of hadron masses is obtained. The relativistic Lagrangian density with the isovector scalar $δ$ meson is used to calculate the nuclear equation of state (EOS) in the framework of the relativistic mean-field (RMF) approach, the effects of the in-medium hadron masses on the properties of neutron stars are finally studied. With the inclusion of the VF corrections, the nuclear EOS becomes softer and the neutron star masses are reduced.

hep-ph↗

arXiv2007

Direct CP violation in $\bar{B}^0 \to ρ^0(ω)ρ^0(ω) \to π^+π^-π^+π^-$

We study the direct CP violation in $\bar{B}^0 \to ρ^0(ω)ρ^0(ω) \to π^+π^-π^+π^-$ (with unpolarized $ρ^0(ω)$) via the $ρ-ω$ mixing mechanism which causes a large strong phase difference and consequently a large CP violating asymmetry when the masses of the $π^+π^-$ pairs are in the vicinity of the $ω$ resonance. Since there are two $ρ(ω)$ mesons in the intermediate state $ρ-ω$ mixing contributes twice to the first order of isospin violation, leading to an even larger CP violating asymmetry (could be 30% -- 50% larger) than in the case where only one $ρ(ω)$ meson is involved. The CP violating asymmetry depends on the Cabibbo-Kobayashi-Maskawa (CKM) matrix elements and the hadronic matrix elements. The factorization approach is applied in the calculation of the hadronic matrix elements with the nonfactorizable effects being included effectively in an effective parameter, $N_c$. We give the constraint on the range of $N_c$ from the latest experimental data for the branching ratios for $\bar{B}^0 \toρ^0ρ^0$ and $\bar{B}^0 \toρ^+ρ^-$. We find that the CP violating asymmetry could be very large (even more than 90% for some values of $N_c$). It is shown that the sensitivity of the CP violating asymmetry to $N_c$ is large compared with its smaller sensitivity to the CKM matrix elements. We also discuss the possibility to remove the mod $(π)$ ambiguity in the determination of the CP violating phase angle $α$ through the measurement of the CP violating asymmetry in the decay $\bar{B}^0\to ρ^0(ω)ρ^0(ω) \to π^+π^-π^+π^-$.

hep-ph↗

arXiv2006

Chiral extrapolation of lattice data for B-meson decay constant

The B-meson decay constant fB has been calculated from unquenched lattice QCD in the unphysical region. For extrapolating the lattice data to the physical region, we propose a phenomenological functional form based on the effective chiral perturbation theory for heavy mesons, which respects both the heavy quark symmetry and the chiral symmetry, and the non-relativistic constituent quark model which is valid at large pion masses. The inclusion of pion loop corrections leads to nonanalytic contributions to fB when the pion mass is small. The finite-range regularization technique is employed for the resummation of higher order terms of the chiral expansion. We also take into account the finite volume effects in lattice simulations. The dependence on the parameters and other uncertainties in our model are discussed.

hep-ph↗

arXiv2006

Earth Matter Effects in Detection of Supernova Neutrinos

We calculated the matter effect, including both the Earth and supernova, on the detection of neutrinos from type II supernovae at the proposed Daya Bay reactor neutrino experiment. It is found that apart from the dependence on the flip probability P_H inside the supernova and the mass hierarchy of neutrinos, the amount of the Earth matter effect depends on the direction of the incoming supernova neutrinos, and reaches the biggest value when the incident angle of neutrinos is around 93^\circ. In the reaction channel \barν_e + p --> e^+ + n the Earth matter effect can be as big as about 12%. For other detection processes the amount of the Earth matter effect is a few per cent.

hep-ph↗

arXiv2005

Chiral Extrapolation of Lattice Data for Heavy Meson Hyperfine Splittings

We investigate the chiral extrapolation of the lattice data for the light-heavy meson hyperfine splittings D^*-D and B^*-B to the physical region for the light quark mass. The chiral loop corrections providing non-analytic behavior in m_πare consistent with chiral perturbation theory for heavy mesons. Since chiral loop corrections tend to decrease the already too low splittings obtained from linear extrapolation, we investigate two models to guide the form of the analytic background behavior: the constituent quark potential model, and the covariant model of QCD based on the ladder-rainbow truncation of the Dyson-Schwinger equations. The extrapolated hyperfine splittings remain clearly below the experimental values even allowing for the model dependence in the description of the analytic background.

hep-lat↗

arXiv2005

Direct CP Violation, Branching Ratios and Form Factors $B \to π$, $B \to K$ in $B$ Decays

The $B \to π$ and $B \to K$ transitions involved in hadronic B decays are investigated in a phenomenological way through the framework of QCD factorization. By comparing our results with experimental branching ratios from the BELLE, BABAR and CLEO Collaborations for all the B decays including either a pion or a kaon, we propose boundaries for the transition form factors $B \to π$ and $B \to K$ depending on the CKM matrix element parameters $ρ$ and $η$. From this analysis, the form factors required to reproduce the experimental data for branching ratios are $F^{B \to π}= 0.31 \pm 0.12$ and $F^{B \to K}= 0.37\pm 0.13$. We calculate the direct CP violating asymmetry parameter, $a_{CP}$, for $B \to π^{+} π^{-} π$ and $B \to π^{+} π^{-} K$ decays, in the case where $ρ-ω$ mixing effects are taken into account. Based on these results, we find that the direct CP asymmetry for $B^{-} \to π^{+} π^{-} π^{-}$, $\bar{B}^{0} \to π^{+} π^{-} π^{0}$, $B^{-} \to π^{+} π^{-} K^{-}$, and $\bar{B}^{0} \to π^{+} π^{-} \bar{K}^{0}$, reaches its maximum when the invariant mass $π^{+} π^{-}$ is in the vicinity of the $ω$ meson mass. The inclusion of $ρ-ω$ mixing provides an opportunity to erase, without ambiguity, the phase uncertainty mod$(π)$ in the determination of the CKM angles $α$ in case of $b\to u$ and $γ$ in case of $b \to s$.

hep-ph↗

arXiv2003

Direct CP Violation in $B \to π^{+} π^{-} π$: Determination of $α$ without discrete ambiguity

Direct CP violation in the hadronic decays $\Bar{B}^{0} \to π^{+}π^{-} π^{0}$ is investigated near the peak of the $ρ^{0}$ taking into account the effect of $ρ- ω$ mixing. Branching ratios for processes $B^{\pm,0} \to ρ^{\pm,0}π^{\pm,0}$ and $B^{-} \to ωπ^{-}$ are calculated as well. We find that the CP violating asymmetry is strongly dependent on the CKM matrix elements. For a fixed $N_{c}^{eff}$, the CP violating asymmetry, $a$, has a maximum of order -40% to -70% for $\Bar{B}^{0} \to ρ^{0}(ω) π^{0}$ when the invariant mass of the $π^{+}π^{-}$ pair is in the vicinity of the $ω$ resonance. The sensitivity of the asymmetry to $N_{c}^{eff}$ is small in that case. Moreover, we find that in the range of $N_{c}^{eff}$ which is allowed by the most recent experimental branching ratios from the BABAR, BELLE and CLEO Collaborations, the sign of $\sin δ$ is always positive. Thus, a measurement of direct CP violation in decays $\Bar{B}^{0} \to π^{+}π^{-} π^{0}$ would remove the mod$(π)$ ambiguity in the determination of the CP violating phase angle $α$.

hep-ph↗

arXiv2003

QCD Factorization in $B$ Decays into $ρπ$

Based on the QCD factorization approach we analyse the branching ratios for the channel $B \to ρπ$. From the comparisons with experimental data provided by CLEO, BELLE and BABAR we constrain the form factor $F^{B \to π}(m_ρ^{2})$ and propose boundaries for this form factor depending on the CKM matrix element parameters $ρ$ and $η$.

hep-ph↗

arXiv2002

Enhanced direct CP violation in $B^{\pm,0} \to π^{+} π^{-} K^{\pm,0}$

We investigate in a phenomenological way, direct CP violation in the hadronic decays $B^{\pm,0} \to π^{+} π^{-} K^{\pm,0}$ where the effect of $ρ- ω$ mixing is included. If $N_{c}^{eff}$ (the effective parameter associated with factorization) is constrained using the most recent experimental branching ratios (to $ρ^{0}K^{0}, ρ^{\pm}K^{\mp}, ρ^{\pm}K^{0}, ρ^{0} K^{\pm}$ and $ωK^{\pm}$) from the BABAR, BELLE and CLEO Collaborations, we get a maximum CP violating asymmetry, $a_{max}$, in the range -25% to $+49%$ for $B^{-} \to π^{+}π^{-} K^{-}$ and -24% to $+55%$ for ${\Bar B}^{0} \to π^{+}π^{-} {\Bar K}^{0}$. We also find that CP violation is strongly dependent on the Cabibbo-Kobayashi-Maskawa matrix elements. Finally, we show that the sign of $\sin δ$ is always positive in the allowed range of $N_{c}^{eff}$ and hence, a measurement of direct $CP$ violation in $B^{\pm,0} \to π^{+} π^{-} K^{\pm,0}$ would remove the mod$(π)$ ambiguity in ${\rm arg}[ - \frac{V_{ts}V_{tb}^{\star}}{V_{us}V_{ub}^{\star}}]$.

hep-ph↗

arXiv2002

Chiral Extrapolation of Lattice Data for Heavy Baryons

The masses of heavy baryons containing a b quark have been calculated numerically in lattice QCD with pion masses which are much larger than its physical value. In the present work we extrapolate these lattice data to the physical mass of the pion by applying the effective chiral Lagrangian for heavy baryons, which is invariant under chiral symmetry when the light quark masses go to zero and heavy quark symmetry when the heavy quark masses go to infinity. A phenomenological functional form with three parameters, which has the correct behavior in the chiral limit and appropriate behavior when the pion mass is large, is proposed to extrapolate the lattice data. It is found that the extrapolation deviates noticably from the naive linear extrapolation when the pion mass is smaller than about 500MeV. The mass differences between Sigma_b and Sigma_b^* and between Sigma_b^{(*)} and Lambda_b are also presented. Uncertainties arising from both lattice data and our model parameters are discussed in detail. We also give a comparision of the results in our model with those obtained in the naive linear extrapolations.

hep-ph↗

arXiv2001

Chiral extrapolation of lattice data for the hyperfine splittings of heavy mesons

Hyperfine splittings between the heavy vector (D*, B*) and pseudoscalar (D, B) mesons have been calculated numerically in lattice QCD, where the pion mass (which is related to the light quark mass) is much larger than its physical value. Naive linear chiral extrapolations of the lattice data to the physical mass of the pion lead to hyperfine splittings which are smaller than experimental data. In order to extrapolate these lattice data to the physical mass of the pion more reasonably, we apply the effective chiral perturbation theory for heavy mesons, which is invariant under chiral symmetry when the light quark masses go to zero and heavy quark symmetry when the heavy quark masses go to infinity. This leads to a phenomenological functional form with three parameters to extrapolate the lattice data. It is found that the extrapolated hyperfine splittings are even smaller than those obtained using linear extrapolation. We conclude that the source of the discrepancy between lattice data for hyperfine splittings and experiment must lie in non-chiral physics.

hep-ph↗

arXiv2001

Heavy quark distribution functions in heavy baryons

Using the Bethe-Salpeter (B-S) equations for heavy baryons Lambda_Q, Sigma_Q, Xi_Q and Omega_Q (Q=b or c), which were established in previous work, we calculate the heavy quark distribution functions in these baryons. The numerical results indicate that these distribution functions have an obvious peak at some fraction, alpha_0, of the baryon's light-cone ``plus'' momentum component carried by the heavy quark, and that as m_Q becomes heavier this peak becomes sharper and closer to 1. The dependence of the distribution functions on various input parameters in the B-S model is also discussed. The results are seen to be qualitatively similar to an existing phenomenological model.

hep-ph↗