arXiv subjects
Publications and source records attributed to Xue-Qian Li.
In this work, we carefully study the energy eigen-values and splitting of heavy quarkonia as there exist $1/r^3$ and $δ^3(\vec r)$ singular terms in the potential which make a direct numerical solution of the Schrödinger equation impossible. We compare the results obtained in terms of perturbation and variational methods with various treatments.
The light quarks inside $B$ mesons are usually treated as spectators and do not affect the decay rates which are assumed to be purely due to b quark decays. In this paper we calculate the non-spectator contributions to inclusive charmless $B$ decays due to the spectator effects. We find that the non-spectator contributions to the branching ratio for $\bar B^0$ are small ($<2\times 10^{-4}$), but the contributions to $ΔS = 0$ and $ΔS = -1$, $B^-$ decay branching ratios can be as large as $-7.5\times 10^{-4}$ and $2\times 10^{-3}$, respectively. These contributions may play an important role in rare charmless $B$ decays.
Based on the present data, the three CKM angles may construct a spherical surface triangle whose area automatically provides a "holonomy" phase. By assuming this geometrical phase to be that in the CKM matrix determined by an unknown hidden symmetry, we compare the theoretical prediction on $ε$ with data and find they are consistent within error range. We also suggest restrictions for the Wolfenstein parameters explicitly, the agreement will be tested by more precise measurements in the future. At least we can claim that such geometrical phase should be part of the weak phase appearing in the CKM matrix, even not the whole.
The wave function at the origin (WFO) is an important quantity in studying many physical problems concerning heavy quarkonia. However, when one used the variational method with fewer parameters, in general, the deviation of resultant WFO from the "accurate" solution was not well estimated. In this paper, we discuss this issue by employing several potential forms and trial wave functions in detail and study the relation between WFO and the reduced mass.
In the heavy quark limit a heavy baryon which contains two heavy quarks is believed to be composed of a heavy diquark and a light quark. Based on this picture, we evaluate the weak semileptonic decay rates of such baryons. The transition form factors between two heavy baryons are associated with those between two heavy mesons by applying the superflavor symmetry. The effective vertices of the W-boson and two heavy diquarks are obtained in terms of the Bethe-Salpeter equation. Numerical predictions on these semileptonic decay widths are presented and they will be tested in the future experiments.
Data show that τ_{B^{\pm}}\simτ_{B^0}, but τ_{D^{\pm}}\sim 2τ_{D^0}. The naive interpretation which attributes τ_{D^{\pm}}\sim 2τ_{D^0} to a destructive interference between two quark diagrams for D^{\pm} decays, definitely fails in the B-case. We investigate Close and Lipkin's suggestion that the phases for producing radially excited states ψ_{2s} in the decay products of B-mesons can possess an opposite sign to the integrals for ψ_{1s} decay products. Their contributions can partially compensate each other to result in τ_{B^{\pm}}\simτ_{B^0}. Since D-mesons are much lighter than B-mesons, such possibilities do not exist in D-decays.
We study the final-state interactions in $B \to πK$ decays through $B \to VV \to πK$ processes where the inelastic rescattering occurs via single pion exchange. The next-to-leading order low energy effective Hamiltonian and BSW model are used to evaluate the weak transition matrix elements and the final-state interactions. We found that the final-state interaction effects in $B \to ρK^* \to πK$ processes are significant. The Fleischer-Mannel relation about the CKM angle $γ$ may be significantly modified.
The relation between CP-violation phase angle and the other three mixing angles in Cabibbo-Kobayashi-Maskawa matrix is postulated. This relation has a very definite geometry meaning. The numerical result coincides surprisingly with that extracting from the experiments. It can be further put to the more precise tests in the future.
To describe possible effects of medium, besides the hamiltonian introduced by Mikheev, Smirnov and Wolfenstein (MSW), in principle, there may exist new terms in the evolution equation for the neutrino oscillation due to the environment. Considering a two-energy-level quantum system: $ν_1-ν_2$, two-species neutrino system which is embedded in a matter environment, we solve the neutrino evolution equation precisely with the possible extra terms, especially, those cause alternations between pure and mixed states of the neutrino quantum system. We obtain some remarkable features for the neutrino oscillations, which are different from that of MSW and accessible to be observed in solar neutrino observation and/or in the planned long-baseline neutrino experiments.
We demonstrate that if the universe is dominated by the massive cold dark matter, then besides the generally believed thermal distribution of the dark matter relics, there may exist some very energetic non-thermal relics of the dark matter particles in the universe from some unknown sources, such as from decay of supermassive X particle released from topological defect collapse or annihilation. Very interesting, we point out that these high energy dark matter particles may be observable in the current and future cosmic ray experiments.
We consider the contributions of both color-singlet and octet $c\bar c$ bound states for studying the suppression of $J/ψ$ production in quark gluon plasma (QGP) and have found that the existence of the color-octet $c\bar c$ may cause the $p_T-$distribution of $J/ψ$ a decrease with $p_T$ after a critical value $(p_T)_{max}$, which is quite different from the behavior in Hadronic Matter (HM).
The eta(1760) may be significantly produced in J/Psi radiative decay. We deduce from experimental data that its branching ratio to two gluons is bounded, 0.4 +- 0.3 < BR(eta(1760) -> gg) < 0.9 +- 0.3, consistent with gluonic admixture. Moreover, the expectation that there should be an isoscalar analogue of the gluonic (hybrid) meson candidate pi(1800) is argued to reinforce hybrid admixture in eta(1760). Two-gluon coupling of hybrids is estimated in a spectator model to be considerably larger than that of quarkonium. In addition, the two-photon coupling of eta(1760) is estimated to be 1.4 +- 0.7 keV.
We study the $ν_μ$ and $ν_τ$ decays in the early epoch of the universe. If $m_{ν_τ}>2m_e$, there would be a CP asymmetry between $ν_τ\rightarrow e^++e^-+ν_e$ and $\barν_τ \rightarrow e^++e^-+\barν_e$. The resultant CP non-invariance is a function of temperature and density and can reach $10^{-7}$ for a reasonable temperature range, but it is noticed that if $m_{ν_τ}>2m_μ\sim 200$ MeV, the CP non-invariance can be much larger.
Making use of the collinear expansion technique developed by Ellis, Furmanski and Petrozio, and the special propagator concept invented by Qiu, we present a factorization approach to the photon fragmentation tensor for the inclusive Lambda hyperon production. As a result, the structure function $\tilde F$, which is related to the transverse polarization of the inclusive Lambda hyperon in unpolarized electron-positron annihilation, is expressed as a combination of four parton fragmentation matrix elements. Since the inclusive $Λ$ production we considered is theoretically the simplest, our study can be taken as a question to the operatability and practability of the first nonleading QCD factorization theorem in the transverse $Λ$ polarization phenomena.
We study possible observational effects of the two Higgs doublets in the $e^+e^- \to b \bar{b} Z^0$ at the LEP II energy. We have found that the observational values can be obviously different from that predicted by the minimal Standard Model (MSM), but the results depend on the parameters of the extended model. The possibilities of the observation are discussed in some details.