N(1535)-Nucleus Potential From Inclusive η-Production Reactions

By using the N~·(1535)model and considering the propagation of the N~· in nuclei,the inclu-sive A(π,η)X and A(γ,η)X reactions are analyzed in the framework of the DWBA.It is found that theNN~· interaction is attractive.The strength of the interaction is less than 50 MeV.

C（γ，η）X反应与N^＊（1535）在核内的性质

在N* (1 53 5)共振模型下 ,研究了γ在原子核上产生η的反应 ,通过N 衰变的实验数据以及γp→ηp反应确定了模型参数 ,结果表明 ,MN =1 550MeV才较好地符合γp→ηp的实验 ,对12 C上的 η介子光生的总截面计算发现 ,N (1 53 5)在核内的宽度由于多体修正而增大 ,N

Strong decays of N~*(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 contributions into account,the description for the strong decays of N*(1535) is improved,especially for the puzzling large ratio of the decays to Nη and Nπ.

Level Crossing of N*(1535)-hole and η Modes and Partial Restoration of Chiral Symmetry in η-mesic Nuclei

We investigate the properties of the η-nucleus interaction by postulating the N*(1535) dominance for ηN system. Since the mass gap of N* and N is very close to the η meson mass,there is the possibility of the level crossing between the N*-h and η modes in finite density. We postulate the N*(1535) resonance for the ηN system and consider quite distinct N* properties in finite density which are predicted by two independent chiral models. We find that we can obtain clearer information on the in-medium N* properties and also on the η-nucleus interaction through the formation of the η-mesic nuclei by (π,N) reactions under the appropriate experimental conditions,which can be performed at existing and/or forthcoming facilities like J-PARC.

Electromagnetic Coupling of Negative Parity Nucleon Resonances N(1535) Based on Nonrelativistic Constituent Quark Model

The electromagnetic transition between the nucleon and excited baryons has long been recognized as an important source of information for understanding strong interactions in the domain of quark confinement. We study the electromagnetic properties of the excitation of the negative parity the N~*(1535) resonances in the nonrelativistic constituent quark model at large momentum transfers and have performed a calculation the longitudinal and transverse helicity amplitudes. Since the helicity amplitudes depend strongly on the quark wave function in this paper, we consider the baryon as a simple, non-relativistically three-body quark model and also consider a hypercentral potential scheme for the internal baryon structure, which makes three-body forces among three quarks. Since the hyper central potential depends only on the hyper radius, therefore, the Cornell potential which is a combination of the Coulombic-like term plus a linear confining term is considered as the potential for interaction between quarks. In our work, in solving the Schrodinger equation with the Cornell potential, the Nikiforov–Uvarov method employed, and the analytic eigen-energies and eigen-functions obtained. By using the obtained eigen-functions, the transition amplitudes calculated. We show that our results in the range Q^2> 2GeV^2 lead to an overall better agreement with the experimental data in comparison with the other three non-relativistic quark models.

Five-quark components in N*(1535)

Here we employ the extended chiral constituent quark model to investigate the five-quark components in the N＊ （1535） resonance. The axial charge of N＊（1535） and the electromagnetic transition γ＊N → N＊（1535） are also analyzed. The results show that there may be sizable strangeness component in N＊（1535）.

A new mechanism for the electromagnetic transition γ^＊N→N^＊（1535）

The heiicity amplitude A1/2^P for the electromagnetic transition γ^＊N→N^＊（1535） is investigated. It is found that a new mechanism γ^＊→q^-q plays an important role in order to improve the description of this transition. On one hand, the A1/2^p is decreased to fall in the data range at the photon point Q^2 = 0, while on the other hand, the new mechanism makes the function A1/2^p（Q^2） to decrease more slowly vs increasing Q^2 as required by the data.

η production in proton-nucleus collisions near threshold

The η-meson production in proton-nucleus （pA） collisions near threshold is studied within a rela- tivistic meson-exchange model. The primary production amplitude is presented in the distorted-wave impulse approximation for the nucleus with isospin 0 or 1 by assuming that N^＊（1535） is excited via a meson exchange and then decays into η and nucleon pair（nN）. Taking ISO and 12C nuclei as examples, we evaluate the prouction cross sections as a function of the incident proton energy, and analyze the effects of nuclear medium and various meson-exchange contributions. Finally we discuss implications for further experimental studies at the Cooling Storage Ring （CSR） in Lanzhou.

氘核上η介子的光产生

计算了阈能附近氘核上η介子的光生反应γｄ→ηＸ．其中核子上η光生过程主要考虑Ｎ（１５３５）的贡献，氘－核子－核子顶角ｄｐｎ矩阵元处理成非相对论氘核波函数．所得截面和微分截面能够很好地符合最新的实验数据，并得出了γｎＮ＊耦合的大小．