Role of the Λ(1600) in the K^-p→Λπ^0π^0 reaction

Role of theΛ(1600)is studied in the K^-p→Λπ^0π^0 reaction by using the effective Lagrangian approach near the threshold.We perform a calculation for the total and differential cross sections by considering the contributions from theΛ(1600)andΛ(1670)intermediate resonances decaying intoπ^0∑^*0(1385)with∑^*0(1385)decaying intoπ^0Λ.Additionally,the non-resonance process from u-channel nucleon pole is also taken into account.With our model parameters,the current experimental data on the total cross sections of the K^-p→Λπ^0π^0 reaction can be well reproduced.It is shown that we really need the contribution from the A(1600)with spin-parity J^P=1/2^+,and that these measurements can be used to determine some of the properties of theΛ(1600)resonance.Furthermore,we also plot theπ0Λinvariant mass distributions which could be tested by the future experimental measurements.     

Strong decays of <Emphasis Type="Italic">N</Emphasis>*(1535) in an extended chiral quark model

The strong decays of the N*(1535) resonance are investigated in an extended chiral quark model by including the low-lying qqqqq components in addition to the qqq component.The results show that these five-quark components in N*(1535) contribute significantly to the N*(1535)→ Nπ and N*(1535) → Nη decays.The contributions to the Nη decay come from both the lowest energy and the next-to-lowest energy five-quarks components,while the contributions to the Nπ decay come from only the latter one.Taking these contr...     

Electromagnetic Properties of S11 States in a Light Cone Quark Model

Using relativistic spin-flavor wave functions of a Lorentz-covariant light cone quark model, we calculate the electromagnetic form factors of two S11 resonances, N（1535） and N（1650）, and the helicity amplitudes A1/2 and S1/2 for electroexcitation of the S11 resonances from the nucleon. The electromagnetic form factors of these S11 resonances are found to be similar to those of the nucleon in shape, while the charge form factor of neutral N（1650） is nearly zero. The relative peak height of the S11 charge form factors is controlled by the mixing angle common to both resonance wave functions. As in most quark models, there is a systematic overestimate of A1/2 in both N（1535） and N（1650） cases at the photon point. A sizeable S1/2 for all cases is produced as suggested by experiments.     

Near-threshold η production in pp collisions

We study near-threshold η meson production in pp collisions within an effective Lagrangian approach combined with the isobar model, by allowing for the various intermediate nucleon resonances due to the π, η, and ρ-meson exchanges. It is shown that the ρ-meson exchange is the dominant excitation mechanism for these resonances,and the contribution from the N*(1720) is dominant. The total cross section data can be reasonably reproduced,and the anisotropic angular distributions of the emitted η meson are consistent with experimental measurements.Besides, the invariant mass spectra of pp and pη explain the data well at excess energy of 15 Me V, and are basically consistent with the data at excess energy of 40 Me V. However, our model calculations cannot reasonably account for the two-peak structure in the pη distribution at excess energies of 57 and 72 Me V, which suggests that a more complicated mechanism is needed at higher energy region.     

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.     

Hadron resonances as rovibrational states

A rovibrational model,including anharmonic,centrifugal,and Coriolis corrections,is used to calculate π,K,N, and Σ orbital and radial resonances.The four orbital excitations of the π meson correspond to the b(1235),π_2(1670),b_3(2030),and π_4(2250) resonances.Its first four radial excitations correspond to the π(1300),π(1800),π(2070),and π(2360) resonances.The orbital excitations of the K meson are interpreted as the K_1(1270),K_2(1770),K_3(2320),and K_4(2500) resonances;its radial excitations correspond to the K(1460) and K(1830) resonances.The N orbital excitations are identified with the N(1520),N(1680),N(2190),N(2220),and N(2600) resonances.The first four radial excitations of the N family correspond to the N(1440),N(1880),N(2100),and N(2300) resonances.The orbital excitations of the Σ baryon are associated with the Σ(1670),Σ(1915),Σ(2100),and Σ(2250) resonances,whereas its radial excitations are identified with the Σ(1660),Σ(1770),and Σ(1880) resonances.The proposed rovibrational model calculations show a good agreement with the corresponding experimental values and allow for the prediction of hadron resonances,thereby proving to be useful for the interpretation of excited hadron spectra.     

Axial charges of N（1535） and N（1650） in two-flavor lattice QCD

We show the lattice QCD results on the axial charge gAN＊-N＊ of negative parity nucleon resonances, N＊（1535） and N＊（1650）, which are key clues to the chiral structure in baryon sector. The measurements are performed with up and down dynamical quarks employing the renormalization-group improved gauge action at β=1.95 and the O（a） improved clover quark action with the hopping parameters, κ=0.1375, 0.1390 and 0.1400. In order to properly separate signals of N＊ （1535） and N＊ （1650）, we construct 2 × 2 correlation matrices and diagonalize them. Wraparound contributions in the correlator, which can be another source of signal contaminations, are eliminated by imposing the Dirichlet boundary condition in the temporal direction. We find that the axial charge of N＊ （1535） takes small values as gAN＊N＊-O（0.1）, whereas that of N＊ （1650） is about 0.5, which is found independent of quark masses and consistent with the predictions by the naive nonrelativistic quark model.     

πN Elastic Scattering and Resonances in Quark Potential Model

The quark potential model is used to investigate the low-energy elastic scattering of πN system. The model potential consists of the t-channel and s-channel one-gluon exchange potentials and the harmonic oscillator confining potential. By means of the resonating group method, a nonlocal effective potential for the πN system is derived from the interquark potentials and used to calculate the πN elastic scattering phase shifts. By considering the effect of QCD renormalization, the suppression of the spin-orbital coupling and the contribution of the color octet of the clusters （qq） and （qqq）, the numerical results are in fairly good agreement with the experimental data. The same model and method are employed to investigate the possible πN resonances. For this purpose, the resonating group equation is transformed into a standard Schrodinger equation in which the nonlocal effective πN interaction potential is included. Solving the Schrodinger equation by the variational method, we are able to reproduce the masses of some currently concerned πN resonances.     

K-p scattering and hyperon excitations in a chiral quark model

A chiral quark-model approach is employed to study theˉ KN scattering at low energies.The processes of Kˉp →Σ 0 π 0,Λπ 0 andˉ K 0 n at P K 800 MeV/c (i.e.the center mass energy W 1.7 GeV) are investigated.The analysis shows that the Λ(1405)S 01 dominates the processes Kˉp →Σ 0 π 0,ˉ K 0 n in the energy region considered here.Around P K 400 MeV/c,the Λ(1520)D 03 is responsible for a strong resonant peak in the cross section of Kˉp →Σ 0 π 0 andˉ K 0 n.To reproduce the data,an unexpectedly large coupling for Λ(1520)D 03 to KN is needed.In contrast,the coupling for Λ(1670)S 01 to KN appears to be weak,which could be due to configuration mixings between Λ(1405)S 01 and Λ(1670)S 01 .By analyzing Kˉ p →Λπ 0,evidences for two low mass S-wave states,Σ(1480)S 11 and Σ(1560)S 11,seem to be available.With these two states,the reaction Kˉp →ˉ K 0 n can also be described well.However,it is difficult to understand the low masses of Σ(1480)S 11 and Σ(1560)S 11 .The s-channel amplitudes for Kˉp →Λπ 0 are also larger than the naive quark model expectations.The non-resonant background contributions,i.e.t-channel and/or u-channel,also play important roles in the explanation of the angular distributions due to amplitude interferences.     

Production of Λ-hypernuclei in A(p,K~ )ΛB reactions

The production of Λ-hypernuclei in the A(p,K )ΛB reaction is investigated in the framework of the distorted wave impulse approximation(DWIA). The total cross sections and differential cross sections for various nuclear targets are calculated with an elementary process pN→NKΛ where the additional contributions from the N*(1535) resonance and the final state interaction between p and Λ are included. The dependence of the production cross sections of Λ-hypernuclei on the phenomenological nuclear density and the nucleon number in the target, as well as the distortion effect of the incident proton and outgoing kaon, are also explored. It is shown that the distortion effect tends to decrease the cross sections by a factor of about 3—10. The production cross sections are sensitive to the adopted nuclear density.     

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.     

Pole Analysis on Unitarized SU(3)× SU(3) One Loop χPT Amplitudes

We analyze ππ-KK and πη-KK couple channel [1,1] matrix Padé amplitudes of SU(3)× SU(3) chiral perturbation theory. By fitting phase shift and inelasticity data, we determine pole positions in different channels (f₀(980), a₀(980), f₀(600), K₀^*(800), K^*(892), ρ(770)) and trace their N_c trajectories. We stress that a couple channel Breit-Wigner resonance should exhibit two poles on different Riemann sheets and meet each other on the real axis when N_c=∞. Poles are hence classified using this criteria and we conclude that K^*(892) and ρ(770) are unambiguous Breit-Wigner resonances. For scalars the situation is much less clear. We find that f₀(980) is a molecular state rather than a Breit-Wigner resonance, while a₀(980), though behave oddly when varying N_c, do maintain a twin pole structure.     

Enhanced K+/π+ Ratio from Central Collisions Between Heavy Nuclei at 1 GeV/Nucleon

We generalized the previous relativistic Vlasov-Uehling-Uhlenbeck model to be able to identify the isospin degree of freedom of particles and used it to simulate the particle production in Au + Au collisions at 1 GeV/nucleon. The momentum spectra of proton, π⁺ and K⁺ particles, the multiplicities of π⁺ and K⁺, and the K⁺/π⁺ ratio as functions of the number of participating nucleons are studied. The theoretical results agree very well with experimental data. We also analyzed the physical origin of the significant rising of K⁺/π⁺ ratio when peripheral collision goes to central collision.     

The Role of a1(1260) in π-p→a1-(1260)p and π-p→π-ρ0p Reactions Near Threshold

We report on a theoretical study of the π^-p→a₁^-(1260) p and π^-p→π^-ρ⁰p reactions near threshold within an effective Lagrangian approach. The production process is described by t-channel ρ⁰ meson exchange. For the π^-p→π^-ρ⁰p reaction, the final π^-ρ⁰ results from the decay of the a₁(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^-p→a₁^-(1260)p reaction. It is shown that, with the coupling constant of the a₁(1260) to ρπ channel obtained from the chiral unitary theory and a cut off parameter Λρ~1.5 GeV in the form factors, the experimental measurement can be reproduced. Furthermore, the total and differential cross sections of π^-p→a₁^-(1260)p→π^-ρ⁰p 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 a₁(1260) resonance and would provide further constraints on the properties of the a₁(1260) state.     

Quasi Three-Body Decay of D Meson

The aim of this work is to provide a phenomenological analysis of the contribution of D~0 meson to K*(892)~0π~+π~-(K*(892)~0-→π~+K~-), K~-π~+ω(ω-→π~+π~-π~0) and K~-π~+?(?(1020)-→ K~+K~-) quasi-three-body decays. The analysis of mentioned multi-body decays is such as to factorize into the three-body decay and several channels observed. Hadronic three-body decays receive both resonant and non-resonant contribution. Based on the factorization method, there are tree and emission annihilation diagrams for these decay modes. In the case of D~0 to vector pseudoscalar states appeared in factored terms, the matrix elements of the vector and axial vector currents between the D~0 and PV mesons can be computed by using D~(*+)pole. Considering the non-resonant and resonant amplitude in our computation,the theoretical values of the branching ratio are(9.78 ± 0.46) × 10~(-3),(2.74 ± 0.17) × 10~(-2), and(3.53 ± 0.23) × 10~(-5), while the experimental results of them are(9.9 ±2.3) × 10~(-3),(2.7 ± 0.5) × 10~(-2), and(4 ± 1.7) × 10~(-5) respectively. Comparing computational analysis values with experimental values show that our results are in approximately agreement with them.     

Bayesian inference of the resonance content of p(γ,K+)Λ

A bayesian analysis of the world's p(γ,K^+)Λ data is presented. From the proposed selection of 11 resonances, we find that the following nucleon resonances have the highest probability of contributing to the reaction: S11(1535), S11(1650), F15(1680), P13(1720), D13(1900), P13(1900), P11(1900), and F15(2000). We adopt a Regge-plus-resonance framework featuring consistent couplings for nucleon resonances up to spin J=5/2. We evaluate all possible combinations of 11 candidate resonances. The best model is selected from the 2048 model variants by calculating the bayesian evidence values against the world's p(γ,K+)Λ data.     

Axial charges of N (1535) and N (1650) in two-flavor lattice QCD

We show the lattice QCD results on the axial charge g~(N~*N~*)_A of negative parity nucleon resonances, N~*(1535) and N~*(1650), which are key clues to the chiral structure in baryon sector. The measurements are performed with up and down dynamical quarks employing the renormalization-group improved gauge action at β=1.95 and the ο(a) improved clover quark action with the hopping parameters, κ=0.1375, 0.1390 and 0.1400. In order to properly separate signals of N~*(1535) and N~*(1650), we construct 2×2 correlation matrices and diagonalize them. Wraparound contributions in the correlator, which can be another source of signal contaminations, are eliminated by imposing the Dirichlet boundary condition in the temporal direction. We find that the axial charge of N~* (1535) takes small values as g~(N~*N~*)～ο(0.1), whereas that of N~*(1650) is about 0.5, which is found independent of quark masses and consistent with the predictions by the naive nonrelativistic quark model.