Heavy Quark Limit of Weak Transition Form Factors in a Light-Cone Constituent Quark Model

In the light-cone constituent quark model, the wavefunction for Λ_b⁰ or Λ_c⁺ with three quarks is reduced to a wavefunction for the heavy-quark-diquark picture by assuming that the two light quarks forming a diquark are in comoving. A heavy quark (or diquark) distribution amplitude is obtained. While form factors of weak transition Λ_b → Λ,ev are calculated in the finite mass case, a hadronic-size-dependen t form of Isgur- Wise function is obtained in the m_Q → ∞ limit.     

Chiral Extrapolation of Lattice Data of Λ_b→Λ_c Form Factors

An extrapolation to the physical limit for the lattice data of Λ_b →Λ_c form factors computed in the nonphysical region is made in this work through a class of fitting functions proposed by us with nonlinear dependence on m2/π derived in the chiral perturbative theory(ChPT) and the heavy quark effective theory(HQET) framework. Then the results are applied to calculate the differential and integrated Λ_b →Λ_c semileptonic decay rates. Meanwhile, a comparison between our results and those obtained through the extrapolation functions with naive linear dependenceon m2/π is made.It is shown that the difference between the extrapolated central values of these two cases is about 5%.The total uncertainties(depending on the momentum transfer q~2) in the linear case are about 5% ～10%(caused by the uncertainties of lattice data) and those in the nonlinear case are about 10% ～ 20%(caused by the uncertainties of both lattice data and input parameters in Ch PT and HQET). More accurate lattice data and parameters in ChPT and HQET are needed to reduce the uncertainties of the extrapolated results.     

Electromagnetic Form Factors of Λbo; and Λc+ in a Relativistic Constituent Quark Model

Light-cone Λ_b^o; and Λ_c⁺ wavefunctions are constructed to calculate their electromagnetic form factors. A new method is presented to calculate the trace and nontrace parts of the current matrix elements and get analytic expressions which are useful to elucidate numerical results.     

Λc重子谱疑难(英文)

Λ_c+重子家族存在一个疑难,也就是重夸克有效理论预言的轨道角动量为L=2的多重态中JP=3/2+的态在实验上是缺失的,而且已发现的Λ_c（2765）+和Λ_c（2940）+的JP量子数仍然未知。在本工作中,我们使用双夸克图像计算了重子的质量,研究了Λ_c（2765）+和Λ_c（2940）+的可能归类以及仍缺失的具有L=2和JP=3/2+量子数的Λ_c+态,进而指出Λ_c（2880）+的峰结构中实际上已经包含了L=2、JP=3/2+这一缺失态,并建议Λ_c（2765）+和Λ_c（2940）+的量子数应分别为2S（1/2+）和2P（1/2-）。There is a puzzle in the Λ_c+ family, i.e., one member with JP=3/2+ is missing in a L=2 multiplet which the heavy quark effective theory predicts, and JP's of Λ_c(2765)+ and Λ_c(2940)+ are unknown. Using a light diquark picture to calculate baryon masses, we study possible assignments of two Λ_c's with unknown JP and the missing Λ_c+ with 3/2+ for L=2, and we find the most probable possibility that the peak corresponding to Λ_c(2880)+ actually includes a missing member with spin 3/2+ for L=2 and that quantum numbers of Λ_c(2765)+ and Λ_c(2940)+ are 2S(1/2+) and 2P (1/2-), respectively.     

Low-Energy Contributions to B (D) → π Form Factor

We calculate low-energy contributions to the weak form factors of B (D) → π in the frameworks of heavy-light chiral perturbation theory (HLCPT) including vector meson effects. The calculation is done to the order 1/Λ_csb³ in the expansion with respect to Λ_csb (Λ_csb is the chiral symmetry breaking scale) at O(1) in 1/m_Q expansion and to 1/Λ_csb² at l/m_Q. It is found that nonperturbative effects dominate B (D) → π form factors and the values are comparable with those from quark model approach.     

Improved analysis of the rare decay processes of Λ_b

It is noted that in the new Particle Data Group(PDG) version the rare decays of the Λ_b baryon have been revised with more accuracy. The new results show that most of the existing theoretical results on the process Λ_b→Λ_γ Lgbare larger than those of experiments. With the improved higher-order light-cone distribution amplitudes of the Λ baryon, we reanalyze the process in the framework of light-cone quantum chromodynamics sum rules and the branching ratio is estimated to be Br (Λ_b→Λ_γ)=(7.38_(-0.39)~(+0.40))×10~(16), which is consistent with the new experimental result. Furthermore, another process Λ_b→Λl~+l~- is also analyzed in the same frame. The final branching ratio is calculated to be Br (Λ_b→Λl~+l~-)=1.20×10~(-6), which is in good accordance with the data from the PDG and other theoretical predictions.     

STUDY OF THE REACTION K-p → πo Λ

It is shown that at high energy all available data for differential and integrated cross sections and the Λ-polarization in the reaction K^-p → π^o Λ can be fitted by using a simple Regge pole model with phenomenological residue functions. The characteristics of helicity and helicity non-flip amplitudes are also examined.     

Contribution of Penguins to the Nonspectator Effects in B-, BO, Λb Decays and the Missing Charm Problem

Taking the nonspectator contributions from the "tree" level four-quark operators and the penguin-induced operators into account we recalculate the charm number n_c in B decays. We find that for B^- and Λ_b, penguin contribution can be neglected, while for B_d^o it is dominant if the nonfactorization factor (t^at^a)is not sizably large. Some new physics may be needed to meet the present data.     

Influence ofΛ Hyperons 1S0 Superfluidity on the Direct Urca Processes with Hyperons

In the framework of the relativistic mean field theory (RMFT), the relativistic energy losses of the direct Urca processes withhyperons (Y-DURCA) for reactionsΛ→p + e +\bar{\nu}_{e} andΞ^- →Λ + e +ν_e arestudied in neutron stars. We calculate the energy gap ofΛ hyperons and investigate the effects of the ¹S₀superfluidity (SF) ofΛ hyperons on the Y-DURCA processes. The calculated results are in line with the recent experimental data\Delta B_ΛΛ∽1.01±0.20^+0.18_-0.11 MeV.The results indicate that the ¹S₀ SF ofΛ hyperons exists in most density ranges of happening the two reactions. The
theoretical cooling curves are in agreement with observation data.     

Observation of CP Non-Invariance in ∑+→Pγ

We study the CP non-invariance in the Δs = 1 weak radiative decay ∑⁺→Pγ based on a few widely-discussed models. In the work, we study the isospin zero channel of the photon where unlike for ∑→Pπ, the CP non-invariance in ∑→Pγ is caused by the interference of the strong interaction to the weak-electromagnetic process through loops. We obtain a CP factor R = (α-α)/(α-α) of an order~10^-5 to 10^-4 which may be observed in the future.     

THE QUARK MASS EFFECT OF THE DISTRIBUTION AMPLITUDES IN γγ-EXCLUSIVE PROCESSES

In this paper we have analyzed the γ^*π°→γ, γγ→ππ and γγ→ρρ processes by using the sum rules of the distribution amplitude ФM(xi,Q²), which are obtained from the π°→γγ and the π→μν decay processes. Since the angular distributions of the γγ→π°π° and γγ→ρ_⊥ρ_⊥ amplitudes are sensitive to the shape of the distribution amplitude ФM(xi,Q²), there is a possibility to investigate the effect of the quark mass from the angular distributions of γγ→MM exclusive processes.     

Some Remarks on the Final State Interactions in B → πK Decays

Careful discussions are made on some points wfiich are met in studying B-decay final state interactions, taking the B⁰ → π + K^- process as an example. We point out that π-exchange rescatterings are not important, whereas for D^* and D^** exchanges, since the B₀ → D+D_s^-, decay has a large branching ratio their contributions may be large enough to enhance the B → πK branching ratio significantly. However our estimates fail to predict a large enhancement.     

Rare Decays B → XS,dνν and XS,d → l+l- in the,Topcolor-Assisted Technicolor Model

We calculate the contributions to the rare decays B → X_S,dνν and X_S,d → l⁺l^- from one-loop Z^o -penguin diagrams in the framework of topcolor-assisted technicolor model. Within the parameter space, we find that: (a) the new contribution from technipions is less than 2% of the standard model prediction; (b) the top-pions can provide a factor of 10 to 30 enhancement to the ratios in question; (c) the topcolor-assisted technicolor model is consistent with the current experimental'data.     

A Vector Dominance Model of the Radiative Decay ∑+ → pγ

In this work, we propose a new mechanism for the ΔS = 1 radiative decay ∑⁺ → pγ, where the reaction occurs via a decay to a proton and a virtual vector meson, which converts later into a real photon by virtue of the vector dominance mechanism. The numerical result shows that this mechanism may be the dominan t one, or at least, very important compared to the others. An implied direct CP violation is also discussed, its order is found to be 10^-4～10^-5     

RADIATIVE DECAY J/ψ→γη′ IN PERTURBATIVE QCD

The deccy rate of J/ψ→γη^′ is calculated by using the light-cone wave function of the flavor singlet pseudoscalar. The result is reasonably in agreement with the experiment.     

Two Higgs Doublet Model III and Double-Lepton Polarization Asymmetries in ∧b→∧μ+μ- Decays

Using the form factors calculated both in lattice QCD and HQET, we analyze the branching ratio, double- lepton polarization asymmetries and averaged double-lepton polarization asymmetries of ∧_b→∧μ⁺μ^- decay in the 2HDM III, respectively. Combining the experimental constrains on the 2HDM III parameters, we take two set of representative parameter spaces in our calculations. For the branching ratio of ∧_b→∧μ⁺μ^- decay, considering the uncertainties of the form factors and input parameters, we find the results of both SM and 2HDM III can satisfy the current experimental data in the framework of lattice QCD, but not in HQET. Then we calculate the double-lepton polarization asymmetries P_ij and their averaged values ij>, we find the double-lepton polarization asymmetries P_LT, P_NN, and P_TT are sensitive to the 2HDM III. However, P_LN, P_NL, P_NT, and P_TN show the opposite results. The contribution of the 2HDM III to their averaged values have similar results.     

A STUDY OF THE REACTION K-P→ΦΛ AC 4.2GeV/c

The high statistics differential cross section, polarisa-tion and density matrix data on K^-P→ΦΛ obtained by the AmsterdamCERN-Nijmegen-Oxford collaboration at 4.2GeV/C is analysed using a Regge pole model with evasive Regge contribu-tions. The exchanges invoked are the K*, K**, K,KA and K_Z The K*-K** exchanges are taken to be non-degenerate and a simplifying assumption on their couplings in O+ζ→O+ζ reactions, advocated recently by Saleem and collaborators, is generalised to the present case. We do not find any need for the K_B in fitting data.     

Electromagnetic form factors of Λ_c in the space-like momentum region

We studied the electromagnetic form factors(EMFFs) of Λ_c and the contributions of the quark and diquark currents to the EMFFs of Λ_c in the space-like region in the Bethe–Salpeter equation approach with instantaneous approximation. In this picture, baryon Λ_c can be regarded as a two-body c(ud) system. We found that for different values of parameters the contribution of quark and diquark currents to the EMFFs of Λ_c is very different,while their total contribution to the EMFFs of Λ_c is similar. The EMFFs of Λ_c are similar to those of other baryons(proton, Ξ~-, and Σ~+) with a peak at ω = 1, where ω = v′·v is the velocity transfer between the initial state(with velocity v) and the final state(with velocity v′) of Λ_c.     

THE EFFECTIVE Λ-α INTERACTION AND TEIE BINDING ENERGY OF Λ IN NYPERNUCLEUS

In this paper,the authors used the effective Λ-a interaction to calculhte more complex hypernucleus.The binding energy of Λ in hypernucleus _Λ⁹Be for K=6 and K=8 was calculated by means of the uncoupled adiabatic approximation.The numerical results were given.It is shown that the calculated results are quite satisfactory.