通过J/Ψ→NM衰变研究N~*时的核子极点效应

研究了J／Ψ→pp^-π衰变过程中核子极点图的贡献，特别是由离壳效应带来的贡献．发现衰变宽度对形状因子是敏感的．在通过用J／Ψ→pp^-π衰变研究N^*时，核子极点图作为背景道的贡献是非常重要的；在通过J／Ψ→pp^-η和pp^-η研究N^*时，核子极点图的贡献可忽略不计；在通过J／Ψ→pp^-ω研究N^*时，核子极点图有明显的贡献． N-pole contributions, especially due to off shell effect, in J/Ψ→ NM decays are carefully studied. It is found that the decay width is sensitive to the form factor. The N pole contribution as a background is important in the J/Ψ→Nπ decay, ignorable in the J/Ψ→Nη and Nη' decays, and sizable in the J/Ψ→Nω decay.     

Re-study of Nucleon Pole Contribution in J/ψ → NN^-π Decay

We re-study nucleon pole contribution in J/ψ → NN^-π decays by including the imaginary part for the propagator of the off-shell nucleon with energy above π N threshold. It is found that when including the imaginary part in the propagator, the branching ratio of the decay width will descend about 11% compared with the result without including the imaginary part, no matter whether including the off-shell form factors or not. It also leads to a phase of up to 25° for the off-shell nucleon propagator at invariant mass around 1400 MeV. This effect needs to be considered for detailed partial wave analysis of N^＊ resonances around this mass region.     

A model to explain the angular distribution of J/Ψ and Ψ(2S) decay into■ and ■

BESⅢ data show a particular angular distribution for the decay of J/Ψ and Ψ(2 S) mesons into ■ andΣ~0Σ~0 hyperons: the angular distribution of the decay Ψ(2 S) →Σ~0Σ~0 exhibits an opposite trend with respect to the other three channels: J/Ψ→■, J/Ψ→Σ~0Σ~0 and Ψ(2 S) →■. We define a model to explain the origin of this phenomenon.     

pp final state interaction in J/ψ →γpp

The phenomenon of the near ppˉ-threshold enhancement observed in the J/ψ→γ pp decay is studied by using the enhancement factor method with a simpler one-pion-exchange potential between p and p. The Jost function caused by the mentioned potential is perturbatively calculated in the zero-th order approximation, and the corresponding enhancement factor is obtained. It is found that such a final state interaction offers an important contribution to the decay width near the ppˉ-threshold, although it is not large enough. To explain the decay data, a phenomenological factor G(p) with the form of 285500/(m 2 π + p 2 ) should be introduced. A further calculation including the p-dependent bare T -matrix, a more realistic N ˉ N potential and the contribution from the higher-order wave functions would provide a better understanding of the decay data and even the existence of the baryonium ppˉ. The near ppˉ-threshold behavior of the decay width in the J/ψ→π 0 pp process is also discussed.     

The X(4140) and X(4160) resonances in the e~+e~-→γJ/ψ? reaction

We investigate the J/Ψ? invariant mass distribution in the e~+e~-→γJ/Ψ? reaction at a center-of-mass energy of ■=4.6 GeV measured by the BESⅢ collaboration,which concluded that no significant signals were observed for e~+e~-→γX(4140) because of the low statistics.We show,however,that the J/Ψ? invariant mass distribution is compatible with the existence of the X(4140) state,appearing as a peak,and a strong cusp structure at the D_s~*■threshold,resulting from the molecular nature of the X(4160) state,which provides a substantial contribution to the reaction.This is consistent with our previous analysis of the B~+→J/Ψ?K~+decay measured by the LHCb collaboration.We strongly suggest further measurements of this process with more statistics to clarify the nature of the X(4140) and X(4160) resonances.     

J/Ψ衰变的Roper共振态结构的研究

通过J/Ψ→p, p*, N**衰变,研究了Roper共振态的混杂态结构对衰变角分布和分支比的影响. 计算结果表明,如果Roper共振态为纯混杂态,那么J/Ψ→p*, N**的角分布几乎相等, 而J/Ψ衰变到混杂态的衰变宽度还不到J/Ψ→p 的1%, 给出了Γ(J/Ψ→ N* )/Γ(J/Ψ→p)和Γ(J/Ψ→ N**)/Γ(J/Ψ→ p)随混合参数的变化关系, 并讨论了在J/Ψ衰变中研究Roper混杂态结构的可能性.The structure of Roper resonance is studied as hybrid states through decays J/Ψ→p*, N** by calculating the angular distributions and decay widths. The results show that the angular distribution parameters for decays J/Ψ→p*, N** are almost equal if the Roper is identified as a pure hybrid state, while their decay width are less the 1% of that for the decay J/Ψ→p, and the variance of the ratio Γ(J/Ψ→N*p)/Γ(J/Ψ→p) and Γ(J/Ψ→N**)/ Γ(J/Ψ→p) with the mixing parameter are presented,and also the scheme to identify the Roper structure in J/Ψ decays is discussed.     

Dispersive analysis of low energyγN→πN process and studies on the N^*(890)resonance

We present a dispersive representation of the γN→πN partial-wave amplitude based on unitarity and analyticity.In this representation,the right-hand-cut contribution responsible for πN final-state-interaction effects is taken into account via an Omnes formalism with elastic πN phase shifts as inputs,while the left-hand-cut contribution is estimated by invoking chiral perturbation theory.Numerical fits are performed to pin down the involved subtraction constants.Good fit quality can be achieved with only one free parameter,and the experimental data regarding the multipole amplitude E0+ in the energy region below the △(1232) are well described.Furthermore,we extend the γN →μN partial-wave amplitude to the second Riemann sheet to extract the couplings of the N*(890).The modulus of the residue of the multipole amplitude E0+(S11pE) is 2.41 mfm·GeV2,and the partial width of N*(890)→ yN at the pole is approximately 0.369 MeV,which is almost the same as that of the N*(1535) resonance,indicating that N*(890) strongly couples to the πN system.     

η-production on the proton via electromagnetic and hadronic probes

The reactions π-p →ηn and γ＇p →ηP are investigated within a dynamical coupledJchannels model of meson production reactions in the nucleon resonance region. The meson-baryon channels included are πN, ηN, π△, σN, and pN. The direct wphotoproduction process is studied within a formalism based on a chiral constituent quark model approach, complemented with a one-gluon-exchange mechanism, to take into account the breakdown of the SU（6）0（3） symmetry. In the models search, the following known nucleon resonances are embodied： Sll （1535）, $11（1650）, Pll （1440）, Pl1（1710）, P13（1720）, D13（1520）, D13（1700）, D15（1675）, and F15（1680）. Data for the π-p →ηnreaction from threshold up to a total center-of-mass energy of W ≈ 2 GeV are satisfactorily reproduced. For the photoproduction channel, two additional higher mass known resonances, P13 （1900） and F15 （2000）, are also considered. However, reproducing the data for γ＇p →ηP requires, within our approach, two new nucleon resonances, for which we extract mass and width.     

Triangle singularity enhancing isospin violation in B~0_s→ J/ψπ~0f_0(980)

We perform calculations for theB~0_s→J/ψπ~0f_0(980) andB~0_s→J/ψπ~0a_0(980) reactions, showing that the first is isospin-suppressed while the second is isospin-allowed. The reaction proceeds via a triangle mechanism, with B~0_s→J/ψK* Kˉ+c.c., followed by the decay K*→Kπ and a further fusion of K Kˉ into the f0(980) or a0(980). We show that the mechanism develops a singularity around the π~0f_0(980) or πa_0(980) invariant mass of 1420 Me V, where the π~0f_0 and π~0a_0 decay modes are magnified and also the ratio of π~0f_0 to π~0a_0 production. Using experimental information for theB~0_s→J/ψK* Kˉ+c.c. decay, we are able to obtain absolute values for the reactions studied which fall into the experimentally accessible range. The reactions proposed and the observables evaluated, when contrasted with actual experiments, should be very valuable to obtain information on the nature of the low lying scalar mesons.     

Study on the Effects of the Light CP-odd Higgs via the Leptonic Decays of Pseudoscalar Mesons

To explain the anomalously large decay rate of Σ+→ p+μ+μ- , it was proposed that a new mechanism where a light CP-odd pseudoscalar boson of mA10 = 214.3 MeV makes a crucial contribution. Later, some authors have studied the transition π0→e+e- and Υ→γA10 in terms of the same mechanism and their result indicates that with the suggested mass one cannot fit the data. This discrepancy might be caused by experimental error of Σ+→p+μ+μ- because there were only a few events. Whether the mechanism is a reasonable one motivates us to investigate the transitions π0→e+e-; η(η′) →μ+μ- ; ηc→μ+μ- ;ηb→τ+τ- within the same framework. It is noted that for π0→e+e-, the standard model (SM) prediction is smaller than the data, whereas the experimental central value of η→μ+μ- is also above the SM prediction. It means that there should be extra contributions from other mechanisms and the contribution of A10 may be a possible one. Theoretically calculating the branching ratios of the concerned modes, we would check if we can obtain a universal mass for A10 which reconcile the theoretical predictions and data for all the modes. Unfortunately, we find that it is impossible to have such a mass with the same coupling |ge|. Therefore we conclude that the phenomenology does not favor such a light A10 , even though a small window is still open.     

A data-driven approach to π~0,η and η′ single and double Dalitz decays

The dilepton invariant mass spectra and integrated branching ratios of the single and double Dalitz decays P→l~+l~-γ and P→l~+l~-l~+l~-(P=π~0,η,η';l=e or μ) are predicted by means of a data-driven approach based on the use of rational approximants applied to π~0,η and η' transition form factor experimental data in the space-like region.     

Probing new physics in B → J/ψπ~0 decay

We calculate the branching ratio of B → J/ψπ0 with a mixed formalism that combines the QCDimproved factorization and the perturbative QCD approaches.The result is consistent with experimental data.The quite small penguin contribution in B → J/ψπ0 decay can be calculated with this method.We suggest two methods to extract the weak phase β.One is through the dependence of the mixing induced CP asymmetry SJ/ψπ0 on the weak phase β,the other is from the relation of the total asymmetry ACP with the weak phase β.Our results show that the deviation ΔSJ/ψπ0 of the mixing induced CP asymmetry from sin（-2β） is of O（10-3） and has much less uncertainty.The above O（10-3） deviation can provide a good reference for identifying new physics.     

N＊（1535） contribution in pp →ppη＇ and pn →dφ

In an effective Lagrangian model we find that the N＊（1535） resonance contribution might be important to the interpretation of the present data of the pp →ppη＇ and pn →dφ reactions. The strong coupling strength of N＊ （1535） to η＇ and φ are indicated, and the possible implication to the intrinsic component of N＊（1535） is explored. These results may provide hints to the real origin of the OZI rule violation. It is stressed that further measurements could be performed at China. the Cooling Storage Ring （CSR） at Lanzhou of     

In-medium pion dispersion relation and medium correction of Nπ■Δ near the threshold energy of pion production

Transport models cannot simultaneously explain very recent data on pion multiplicities and pion charged ratios from central collision of Sn+Sn at 0.27 A GeV.This stimulates further investigations on the pion dispersion relation,in-medium Nπ→Δ cross sections,and Δ→Nπ decay widths near the threshold energy or at subthreshold energy of pion production in isospin asymmetric nuclear matter.In this study,the pion dispersion relation,in-medium Nπ→Δ cross section,and Δ→Nπ decay width near the threshold energy are investigated in isospin asymmetric nuclear matter by using the one-boson-exchange model.With the consideration of the energy conservation effect,the in-medium Nπ→Δ cross sections are enhanced at s1/2 <1.11 GeV in a nuclear medium.The prediction of pion multiplicity and π-/π+ ratios near the threshold energy could be modified if this effect is considered in transport model simulations.     

Production of P_(cs) (4459) from Ξ_b Decay

Inspired by the P_(cs)(4459) reported by the LHCb collaboration recently,we investigate the P_(cs)(4459) production from Ξ_b decay in a molecular scenario using an effective Lagrangian approach.With different J~P assignments to P_(cs)(4459),the magnitude of branching fractions of Ξ_b→ P_(cs)(4459)K is estimated,which is of the order of 10-4.Together with the decay properties of P_(cs)(4459),the present estimations could be further testified by precise measurements and contribute to a better understanding of the molecular interpretations and the exploration of J~P quantum numbers of P_(cs)(4459).     

Partial wave analysis of ψ' →γχ_(c0) →γpK-Λ used for searching for baryon resonance

Abundant ψ' events have been collected at the Beijing Electron Positron Collider-Ⅱ (BEPCⅡ) that could undoubtedly provide us with a great opportunity to study the more attractive charmonium decays. As has been noticed before, in the process of J/ψ' decaying to the baryonic final states, pK-Λ, the evident Λ* and N* bands have been observed. Similarly, by using the product of χcJ from ψ' radiative decay, we may confirm this or find some extra new resonances. χc0's data samples will be more than χc1,2, taking into account the larger branching ratio of ψ' →γχc0. Here, we provide explicit partial wave analysis formulae for the very interesting channel ψ' →γχc0 →γpK-Λ.     

Searching for Electrical Dipole and Chromodipole Moments of a Charm Quark in J／ψ→γφφ Decay

We propose a scheme to search for the electrical dipole moments (EDMs) and chromodipole moments (CDMs) of a charm quark in the decay J/ψ→γφφ based on J/ψ data samples accumulated on the Beijing Electron Positron Collider (BEPC). The EDM and CDM interactions are introduced in this decay and then we relate them to some CP asymmetrical observables, which are predicted in the valence quark model. We propose a method to hunt for these values by measuring associated CP asymmetrical observables, and we also discuss the prospect of such measurement on the BEPC.     

The Role of α_1(1260) in π~-p→α_1~-(1260)p and π~-p → π~-ρ~0p Reactions Near Threshold

We report on a theoretical study of the π~-ρ→α1(1260)p and π~-ρ→π~-ρ~0p reactions near threshold within an effective Lagrangian approach.The production process is described by t-channel ρ~0 meson exchange.For the π~-ρ→π~- ρ~0p reaction,the final π~-ρ~0 results from the decay of the α1(1260) resonance,which is assumed as a dynamically generated state from the K* K and ρπ coupled channel interactions.We calculate the total cross section of the π~-ρ→α1(1260)p reaction.It is shown that,with the coupling constant of the α1(1260) to ρπ channel obtained from the chiral unitary theory and a cut off parameter Δρ~1.5 GeV in the form factors,the experimental measurement can be reproduced.Furthermore,the total and differential cross sections of π~p→α1(1260)p→π~ρ~0p reaction are evaluated,and it is expected that our model calculations can be tested by future experiments.These reactions are important for the study of the α1(1260) resonance and would provide further constraints on the properties of the α1(1260) state.     

J／φ→γBB Decays and the Quark—pair Creation Model

We generalize the quark-pair creation model to a study of the radiative decays J/φ→γBB by assuming that the u.d,or s quark pairs are created with the same interaction strength,From the calculation of the ratio of the decay widths （J/φ→γpp)/Γ（J/φ→pp),we extract the quark-pari creation strength gI=15.40GeV,Based on the SU(6)spin-flavour basis and the “uds” basis,the radiative decay branching ratios cotaining strange baryons are evaluated.Measurements for these decay widths from the BESII data are suggested.     

ηb decay into charmonium in association with cc pair

We calculate the inclusive decay rates of ηb into charmonium via double c~ pairs for S- and P-wave states ηc, J/ψ and XcJ within the framework of non-relativistic QCD （NRQCD） factorization at leading order in αs. Besides calculating the contributions of the color-singlet channels ηb → cc[2s＋1SL^（1）]＋cc, the effects of cc pair in the color-octet configurations are also considered. We find that ηb → cc[3S1^（8）] ＋cc make a small contribution to Br（ηb →J/ψ（ηc）＋cc）. While in the ηb →XcJ ＋cc case, the color octet contributions are significant, for they are of the same a 5 order as the color-singlet processes. We predict Br（ηb →J/ψ（ηc）＋cc） = 2.99（2.75） × 10^-5 Vc for S-wave states J/ψ and ηc, and Br（ηb → XcJ ＋cc） = （4.37, 3.40, 2.83） × 10^-5 （for J = 0,1, 2） for P-wave states XcJ. In the end, we also find Br（ηb → cccc） is almost saturated by ηb decay into charmonium in association with cc pair from the point of view of duality.