Role of t-channel meson exchanges in S-wave πN and KN scatterings

The low-energy S-wave πN and KN scatterings are studied by using the K-matrix approach within the meson exchange framework.The t-channel meson exchanges,especially ρ and σ exchanges,are found to play a very important role in these two processes.The t-channel ρ exchange determines the isospin structure of the scattering amplitudes,it gives attractive force in the low isospin state but repulsive force in the high isospin state.The t-channel σ exchange gives a very large contribution in these two processes,while it is negligible in meson-meson S-wave scatterings.     

Magnetic field induced phase branches of the superconducting transition in two-dimensional square π-loop arrays

Based on the results of explicit forms of free energy density for each possible arrangement of magnetization fluxes in large-scale two-dimensional (2D) square $\pi $-loop arrays given by Li \textit{et al} [2007 {\em Chin. Phys.} {\bf 16} 1450], the field-cooled superconducting phase transition is further investigated by analysing the free energy of the arrays with a simplified symmetrical model. Our analytical result is exactly the same as that obtained in Li's paper by means of numerical calculations. It is shown that the phase transition splits into two branches with either ferromagnetic or anti-ferromagnetic flux ordering, which depends periodically on the strength of external magnetic flux $\phi_{\e}$ through each loop and monotonically on the screen parameter $\beta $ of the loops in the arrays. In principle, the diagram of the phase branches is similar to that of its one-dimensional counterpart. The influence of thermal fluctuation on the flux ordering during the transition from normal to superconducting states of the $\pi $-loop arrays is also discussed.     

Branching ratio and CP asymmetry of Bs→K0(1430)η(') decays in the PQCD approach

In the two-quark model supposition for K0*(1430), which can be viewed as either the first excited state (ScenarioⅠ) or the lowest lying state (Scenario Ⅱ), the branching ratios and the direct CP-violating asymmetries for decays s0 → K0*0(1430)η (’) are studied by employing the perturbative QCD factorization approach. We find the following results: (a) The CP averaged branching ratios ofs0 → K0*0 (1430)η ands0→ K0*0(1430)η’ are small and both in the order of 10-7 . If one views K0* (1430) as the lowest lying state, B(s0→K0*0(1430)η) ≈ 3.9×10-7 and B(s0→K0*0(1430)η’) ≈ 7.8×10-7.(b) While the direct CP-violating asymmetries of these two decays are not small: if we still take the parameters of K0* (1430) in scenario , ACPdir(s0→K0*0(1430)η) ≈ 56.2% and ACPdir(s0→ K0*0(1430)η’) ≈ 42.4%. (c) The annihilation contributions will play an important role in accounting for future data, because both the branching ratios and the direct CP asymmetries of these two decays are sensitive to the annihilation type contributions.     

Roles of N?→NN and πN→? Reactions in Heavy-Ion Collisions at Intermediate Energies

Within the framework of the isospin-dependent transport model, the roles of the reactions N? → NN and πN→ ? are investigated through simulating heavy-ion collisions at 1000 MeV/nucleon. The absorption process N? → NN plays an important role for heavy impact systems and small impact parameters than for light impact systems and large impact parameters. The resorption process πN→ ? is of importance for heavy impact systems and large impact parameters than for light impact systems and small impact parameters. Thus the influences of the reaction N? → N N(πN→ ?) on pion production dynamics can be neglected in heavy-ion collisions for smaller(larger) impact parameters and light systems. It is the reaction πN→ ? that causes the anti-correlation of pions and nucleons in the rapidity dependence of the directed flow.     

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.     

Radial excitation states of η and η' in the chiral quark model

A chiral quark model is applied to calculate the spectra of pseudoscalar mesons η and η'. By analyzing the obtained spectra, we find that the mesons η'(2¹S₀), η(4¹S₀), η'(3¹S₀) and η'(4¹S₀) are the possible candidates of η(1760), X(1835), X(2120) and X(2370). The strong decay widths of these pseudoscalars to all the possible two-body decay channels are calculated within the framework of the ³P₀ model. Although the total width of η'(2¹S₀) is compatible with the BES Collaboration's experimental value for η(1760), the partial decay width to ωω is too small, which is not consistent with the BES result. If X(1835) is interpreted as η(4¹S₀), the total decay width is compatible with the experimental data, and the main decay modes will be mπ a₀(980) and m π a₀(1450), which needs to be checked experimentally. The assignment of X(2120) and X(2370) to η'(3¹S₀) and η'(4¹S₀) is disfavored in the present calculation because of the incompatibility of the decay widths.     

Radial excitation states of η and η′ in the chiral quark model

A chiral quark model is applied to calculate the spectra of pseudoscalar mesons η and η . By analyzing the obtained spectra, we find that the mesons η (2 1 S 0 ), η(4 1 S 0 ), η (3 1 S 0 ) and η (4 1 S 0 ) are the possible candidates of η(1760), X(1835), X(2120) and X(2370). The strong decay widths of these pseudoscalars to all the possible two-body decay channels are calculated within the framework of the 3 P 0 model. Although the total width of η (21S0 ) is compatible with the BES Collaboration’s experimental value for η(1760), the partial decay width to ωω is too small, which is not consistent with the BES result. If X(1835) is interpreted as η(4 1 S 0 ), the total decay width is compatible with the experimental data, and the main decay modes will be πa 0 (980) and πa 0 (1450), which needs to be checked experimentally. The assignment of X(2120) and X(2370) to η (31S0 ) and η (41S0 ) is disfavored in the present calculation because of the incompatibility of the decay widths.     

Production of a0-mesons in the reactions πN↦a0N and pp↦da0 + at GeV energies

We investigate the reactions πN↦a ₀ N and pp↦da ₀ ⁺ near threshold and at medium energies. An effective Lagragian approach and the Regge pole model are applied to analyze different contributions to the cross-section of the reaction πN↦a ₀ N. These results are used to calculate the differential and total cross-sections of the reaction pp↦da ₀ ⁺ within the framework of the two-step model in which two nucleons produce an a₀-meson via π-meson exchange and fuse to a deuteron. The necessity of new measurements on a₀ production and branching fractions (of its decay to the K and πη channels) is emphasized for clarifying the a₀ structure. Detailed predictions for the reaction pp→da ₀ ⁺ are presented for the energy regime of the proton synchrotron COSY-Jülich. Received: 4 August 2000 / Accepted: 17 September 2000     

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.     

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.     

Signature splitting of the πh11/2 band and high-spin structures in 155Tb

Seven experimentally observed bands of 155Tb are analyzed in detail,using the particle-number-conserving method for treating the cranked shell model with monopole and quadrupole pairing interactions.We satisfactorily reproduce the experimental alignments and especially focus on the microscopic mechanism of the second back-bending and the influence of pair interaction on ultrahigh spins.Our calculated results show that the πi13/2 orbitals are too high to give a contribution to the moment of inertia below ω≈ 0.7 MeV.Instead,the crossing between the π[541]1/2 and other proton orbitals is responsible for the second back-bending.We assign a possible configuration to the decoupled band found in 155Tb and predict eleven bands which are experimentally unobserved.     

Effects of electron correlation and the Breit interaction on one- and two-electron one-photon transitions in double K hole states of He-like ions(10 ≤ Z ≤ 47)

The x-ray energies and transition rates associated with single and double electron radiative transitions from the double K hole state 2s2p to the 1s2s and 1s^2 configurations of 11 selected He-like ions(10 ≤ Z ≤ 47) are calculated using the fully relativistic multi-configuration Dirac–Fock method(MCDF). An appropriate electron correlation model is constructed with the aid of the active space method, which allows the electron correlation effects to be studied efficiently. The contributions of the electron correlation and the Breit interaction to the transition properties are analyzed in detail. It is found that the two-electron one-photon(TEOP) transition is correlation sensitive. The Breit interaction and electron correlation both contribute significantly to the radiative transition properties of the double K hole state of the He-like ions. Good agreement between the present calculation and previous work is achieved. The calculated data will be helpful to future investigations on double K hole decay processes of He-like ions.     

Reinvestigation of the high spin states in ^（161）Er and enhanced E1 transitions in the N=93 isotones

High-spin states in ¹⁶¹Er have been studied experimentally using the ¹⁵⁰Nd(¹⁶O, 5n) reaction at a beam energy of 86 MeV. The relatively enhanced E1 transitions between the 5/2⁺[642] and 3/2^-[521] bands are observed in ¹⁶¹Er, and the B(E1) values are extracted experimentally. The systematics of the R(E1) values in the N=93 isotones are presented. It is found that the strength of the E1 transitions obviously exhibits angular momentum dependence, and the occurrence of the relatively enhanced E1 transitions could be attributed to octupole softness.     

Isotopic Symmetry Breaking in the η(1405) → f0(980)π0 → π+π–π0. Decay through a $$K\bar K$$ Loop Diagram and the Role of Anomalous Landau Thresholds

Anomalous isotopic symmetry breaking in the η(1405) → f₀(980)π⁰ → π+π–π⁰ decay through a mechanism featuring anomalous Landau thresholds in the form of logarithmic triangle singularities, i.e., through the \(\eta (1405) \to (K*\bar K + \bar K*K) \to ({K^ + }{K^ - } + {K^0}{\bar K^0}){\pi ^0} \to {f_0}(980){\pi ^0} \to {\pi ^ + }{\pi ^ - }{\pi ^0}\) transition, has been analyzed. It has been shown that this effect can be correctly quantified only by taking into account the nonzero K* width. Different scales of isotopic symmetry breaking associated with the K⁺–K⁰ mass difference are compared.     

Reply to a comment by S.N. Semenov and M.E. Schimpf on ‘Role of the velocity frame of reference in thermodiffusion in liquid mixtures’, Philosophical Magazine vol. 92, 705 (2012), by M. Eslamian,C.G. Jian and M.Z. Saghir.

A small angle X-ray scattering (SAXS) study of nanovoids in 99.988 and 99.995?at.% aluminium is presented. Absolute intensity calibration using a glassy carbon standard is used to extract the weak SAXS signature from nanovoids introduced by thermal quenching. SAXS analysis methods, including Guinier, Porod and Indirect Transform, are used to obtain values for the void–size, number distribution and volume fraction, as well as measures of the void-metal matrix interface structure in quenched aluminium samples. The SAXS analysis has identified a residual impurity effect on void formation and has been used to characterize trends in nanovoid size, number distribution and interface structure as a function of ageing time at elevated temperatures (artificial ageing). The work presented here, including identification of experimental tools that can be readily improved, demonstrates that SAXS studies are capable of providing precise characterization of nanovoid structure in aluminium. This level of information will be useful in developing phenomenological models of void nucleation and growth capable of linking atomic scale phenomena to macroscopic material properties.     

Study of K*(892)0andФ(1020)meson production in proton–proton and Pb–Pb collisions at√SNN=2.76 TeV

In this paper,we describe a study of charged particle yield as a function of pT for K^*(892)0 and phgr(1020)mesons in proton–proton(pp)and Pb–Pb collisions at√S_NN=2.76 TeV in the central rapidity region of|y|<0.5,in a pT range of 0?1in pp collisions and in a pT range of 0NN=2.76 TeV.It was concluded that the models'predictions for the phgr-meson in pp and for the most central Pb-Pb collisions disagreed with the ALICE data,and that the difference increased with pT.This may be connected with the essential role of collective parton behaviors which could not have been taken into account by the models.For K^*0 mesons,both programs gave almost the same predictions,and with pT in the interval pT>3 GeV c^?1,the predictions were very close to the experimental data.Both models gave higher predictions for the soft pT interval and lower predictions for the hard interactions.The values of the RAA distributions were lower than unity and both models were very close to the ALICE data.It is very interesting that the models were not able to describe the pT distributions,but they gave good predictions for their ratios.This may possibly be due to parton collective behaviors.We observed some additional suppression of K^*0 at low values of pT with respect to phgr-mesons,which may be related to the role of the masses of the particles in soft interactions.The rising trend for R_AAin the region from pT=10 GeV c^?1to 20 GeV c^?1 observed by the ALICE experiment was absent for theФ-mesons.