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Xue-Qian Li

Publications and source records attributed to Xue-Qian Li.

At least 181 records · Page 10Linked to original sources
arXiv2002

Molecular States and 1^-+ Exotic Mesons

This work investigates whether the observed 1^-+ exotic mesons are molecular states. We first use a potential model to calculate the spectra and lifetimes of the f_0(980) and a_0(980), taken to be loosely bound molecular states of K Kbar, then apply the same scenario to the 1^-+ exotic states pi_1(1400) and pi_1(1600), assuming them to be pi eta(1295) and pi eta(1440) molecules respectively. We derive the effective potential in the framework of field theory at the hadronic level. Our results indicate that the present data on pi_1(1400) and pi_1(1600) rule out the specific molecular ansatz. We show that the lifetime of a loosely bound heavy-light molecule with enough angular momentum is fully determined by the lifetimes of its constituent mesons.

hep-ph↗
arXiv2002

Strange sea asymmetry in nucleons

We evaluate the medium effects in nucleon which can induce an asymmetry of the strange sea. The short-distance effects determined by the weak interaction can give rise to $δm\equiv Δm_s-Δm_{\bar s}$ where $Δm_{s(\bar s)}$ is the medium-induced mass of strange quark by a few KeV at most, but the long-distance effects by strong interaction could be sizable.

hep-ph↗
arXiv2001

Applicability of the Friedberg-Lee-Zhao method

Friedberg, Lee and Zhao proposed a method for effectively evaluating the eigenenergies and eigen wavefunctions of quantum systems. In this work, we study several special cases to investigate applicability of the method. Concretely, we calculate the ground-state eigenenergy of the Hellmann potential as well as the Cornell potential, and also evaluate the energies of the systems where linear term is added to the Coulomb and harmonic oscillator potentials as a perturbation. The results obtained in this method have a surprising agreement with the traditional method or the numerical results. Since the results in this method have obvious analyticity compared to that in other methods, and because of the simplicity for calculations this method can be applied to solving the Schrödinger equation and provides us better understanding of the physical essence of the concerned systems. But meanwhile applications of the FLZ method are restricted at present, especially for certain potential forms, but due to its obvious advantages, it should be further developed.

hep-ph↗
arXiv2001

Asymmetry of Strange Sea in Nucleons

Based on the finite-temperature field theory, we evaluate the medium effects in nucleon which can induce an asymmetry between quarks and antiquarks of the strange sea. The short-distance effects determined by the weak interaction can give rise to $δm\equiv Δm_s-Δm_{\bar s}$ where $Δm_{s(\bar s)}$ is the medium-induced mass of strange quark by a few KeV at most, but the long-distance effects by strong interaction are sizable. Our numerical results show that there exists an obvious mass difference between strange and anti-strange quarks, as large as 10-100 MeV.

hep-ph↗
arXiv2001

|Delta B|=1 Weak Effective Lagrangian in the Minimal Flavor Violation Supersymmetry

To evaluate the weak decays of b-hadrons, the $ΔB=1$ weak effective Lagrangian is the foundation. Any new physics beyond the standard model (SM) would contribute to the effective Lagrangian through the loop integration at the weak scale and evolution from the weak scale down to the hadronic scale. In this work we present a systematic analysis on the effective Lagrangian which mediates hadronic $|ΔB|=1$ processes in the framework of the minimal flavor violation supersymmetry as well as a numerical evaluation of the Wilson coefficients in the effective theory.

hep-ph↗
arXiv2001

Study of the $B_c$-meson lifetime

We in terms of optical theorem estimate the lifetime of $B_c-$meson with the parameters which are deturmined by fitting the data for the lifetimes and inclusive semilepton-decays of various $B$ and $D$ mesons. In the estimate, we find that the bound-state effects are important, and take them into account carefully in the framework which attributes the effects to the effective masses of the decay heavy quarks in the inclusive processes. We also find that to $B_c$ lifetime the penguin contribution is enhanced due to possible interference between the penguin and the `tree part' $c_1O_1+c_2O_2$.

hep-ph↗
arXiv2000

Neutrino Oscillations in Supersymmetry without Lepton number conservation and R-parity

With the on-shell renormalization scheme, we discuss neutrino masses up to one-loop approximation in the Supersymmetry without lepton number conservation and R-parity. Ii is shown that in this model with experimentally allowed parameters, $Δm^2_{23}, Δm^2_{12}$ and the mixing angles $|\sinθ{23}|,|\sinθ_{12}|$ which are consistent with the present observation values can be produced. We find that small neutrino mass ($\leq$ 1 eV) sets a loose constraint on the R-parity violation parameters in the soft breaking terms.

hep-ph↗
arXiv2000

Complete analysis on the next-to-leading order supersymmetric QCD corrections to $B^0-\bar{B}^0$ mixing

We present a complete next-to-leading-order calculation of the QCD corrections to $B^0-\bar{B}^0$ ($K^0-\bar{K}^0$) mixing in the framework of the minimal flavor violating (MFV) supersymmetry. We take into account the contributions from the gluino and find that the gluino-mediated corrections modify the LO result obviously even when the mass of gluino $m_{\tilde{g}} \gg m_{\rm w}$. In general, one cannot neglect gluino contributions.

hep-ph↗
arXiv2000

The lifetime of B_c-meson and some relevant problems

The lifetime of the B_c-meson is estimated with consistent considerations on all of the heavy mesons ($B^0, B^\pm, B_s, D^0, D^\pm D_s$) and the double heavy meson B_c. In the estimate, the framework, where the non-spectator effects for nonleptonic decays are taken into account properly, is adopted, and the parameters needed to be fixed are treated carefully and determined by fitting the available data. The bound-state effects in it are also considered. We find that in decays of the meson B_c, the QCD correction terms of the penguin diagrams and the main component terms c_1O_1, c_2O_2 of the effective interaction Lagrangian have direct interference that causes an enhancement about 3 ~ 4% in the total width of the B_c meson.

hep-ph↗
arXiv2000

Electromagnetic radiation of baryons containing two heavy quarks

The two heavy quarks in a baryon which contains two heavy quarks and a light one, can constitute a scalar or axial vector diquark. We study electromagnetic radiations of such baryons, (i) Ξ_{(bc)_1} -> Ξ_{(bc)_0}+γ, (ii) Ξ_{(bc)_1}^* -> Ξ_{(bc)_0}+γ, (iii) Ξ_{(bc)_0}^{**}(1/2, l=1) -> Ξ_{(bc)_0}+γ, (iv) Ξ_{(bc)_0}^{**}(3/2, l=1) -> Ξ_{(bc)_0}+γand (v) Ξ_{(bc)_0}^{**}(3/2, l=2) -> Ξ_{(bc)_0}+γ, where Ξ_{(bc)_{0(1)}}, Ξ^*_{(bc)_1} are S-wave bound states of a heavy scalar or axial vector diquark and a light quark, and Ξ_{(bc)_0}^{**}(l is bigger than 1) are P- or D-wave bound states of a heavy scalar diquark and a light quark. Analysis indicates that these processes can be attributed into two categories and the physical mechanisms which are responsible for them are completely distinct. Measurements can provide a good judgment for the diquark structure and better understanding of the physical picture.

hep-ph↗
arXiv2000

Search for Ambient Neutralino Dark Matter at Accelerator

We investigate the possibility of using accelarator beam particles to collide with the ambient neutralino dark matter particles in cosmic rays as a way to search for the cold dark matter. We study in detail its inelastic and elastic scattering with the projectile particles at electron-positron colliders and discuss the possible experimental signals and the relevent background.

hep-ph↗
arXiv2000

Bose Symmetry Interference Effects of $4π$ Final States

We carefully analyze the relative branching ratios of $4π$ final states $π^+π^-π^+π^-$, $π^+π^-π^0π^0$ and $π^0π^0π^0π^0$, from various resonances of $J^{PC}=0^{++}$, $0^{-+}$, $2^{++}$. We find that the Bose symmetry interference effects would make their ratios to obviously differ from the naive counting values without considering these effects. The results should be applied to estimate correctly various $4π$ decay branching ratios of relevant resonances.

hep-ph↗
arXiv1999

Application of Hypervirial Theorem As Criteria For Accuracy of Variational Trial Wave Function

It would be interesting to investigate the accuracy of the results obtained in the variational method, because it is important for studying hadron spectra. One can define some criteria to judge the accuracy, or the quality of the trial function. We employ a simple potential form to check how accurate the variational results obtained by a single-parameter trial function can be. All the concerned problems, in particular, the relevant aspects on the application of hypervirial theorem in variational method for various potential forms, are discussed in every detail. The qualitative conclusion of the work can be generalized to much more complicated cases. Our study suggests that the hypervirial relations can serve as a good and practical criterion for judging the accuracy of any trial functions.

hep-ph↗
arXiv1999

Spectra of Baryons Containing Two Heavy Quarks in Potential Model

In this work, we employ the effective vertices for interaction between diquarks (scalar or axial-vector) and gluon where the form factors are derived in terms of the B-S equation, to obtain the potential for baryons including a light quark and a heavy diquark. The concerned phenomenological parameters are obtained by fitting data of $B^{(*)}-$mesons instead of the heavy quarkonia. The operator ordering problem in quantum mechanics is discussed. Our numerical results indicate that the mass splitting between $B_{3/2}(V), B_{1/2}(V)$ and $B_{1/2}(S)$ is very small and it is consistent with the heavy quark effective theory (HQET).

hep-ph↗
arXiv1999

Comment on " a unified scheme for flavored mesons and baryons"

We would comment on the results of the paper "a unified scheme for flavored mesons and baryons" (P.C.Vinodkumar, J.N.Panandya, V.M.Bannur, and S.B.Khadkikar Eur. Phys. J. A4(1999)83), and point out some inconsistencies and mistakes in the work for solving the Dirac equation. In terms of an example for a single particle we investigate the reliability of the perturbative method for computing the Coulomb energy and discuss the contribution to the wavefunction at origin from the Coulomb potential. We conclude that the accuracy of their numerical results needs to be reconsidered.

hep-ph↗
arXiv1999

Further Study On U(1) Gauge Invariance Restoration

To further investigate the applicability of the projection scheme for eliminating the unphysical divergence $s/m_e^2$ due to U(1) gauge invariance violation, we study the process $e^-+W^+\to e^-+\bar t+b$ which possesses advantages of simplicity and clearness. Our study indicates that the projection scheme can indeed eliminate the unphysical divergence $s/m_e^2$ caused by the U(1) gauge invariance violation and the scheme can apply to very high energy region.

hep-ph↗
arXiv1999

Non-Spectator Diquark Effects on Lifetimes of Λ_b, Ω_{b}^{(*)} and Weak Decay Rates of Σ_{b}^{(*)}, Ξ_{b}^{(*)}

The difference of τ_{_B} and τ_{_{Λ_b}} indicates the role of the light flavors. We calculate the lifetimes of B-meson and Λ_b based on the weak effective Hamiltonian while assuming the heavy baryon is constructed by a heavy b-quark and a diquark containing two light quarks. In this scenario, we use the information of the measured ratio τ_{_{Λ_b}}/τ_{_B} as input to predict rates of the inclusive weak decays of Σ_{b}^{(*)} and Ξ_{b}^{(*)} into non-bottom final states. We find that these rates of Σ_{b}^{(*)} and Ξ_{b}^{(*)} are much larger than that of B-mesons and Λ_b. We also give the predictions for the lifetimes of Ω_b and Ω_{b}^{*}. Phenomenological implication of our result is discussed.

hep-ph↗