STUDY OF MEDIUM EFFECT IN HADRON MANY-BODY SYSTEM AT DEEP INSIDE OF NUCLEI

在QCD和QHD（量子流体动力学）的框架下，理论上预测了核场中强子质量的修正是由于手性对称性的部分恢复或核子狄拉克旋量在强标量场中的低分量增强的表现。在几百MeV的入射能量下，基于介子交换力的理论模型很好地描述了核子之间的相互作用。因此，预计这些质量修饰会引起神经网络相互作用的修饰，这种修饰在某些核反应中是可以检测到的。核子准自由散射是这类反应中的一种，可以看作是核场中的神经网络散射，适合于研究核场中的神经网络相互作用。TRIUMP人首先发现，导致1/ 5空穴态的（p,2p）反应的分析能力与自由p-p散射值相比有明显的降低。在RCNP，这种减少是s…更多地被认为是单调的密度相关的，这表明存在一些介质效应。对于7Li目标，在1gev时也观察到这种减少。在本研究中，我们测量了PNPI在1gev下（p,2p）反应的极化。采用双臂磁谱仪系统进行测量，每台光谱仪上使用由碳分析仪和MWPC组成的焦平面偏振仪来测量出射质子的偏振。我们发现，使用自由神经网络相互作用的计算值显示出强烈的密度依赖减少。这个结果与392 MeV的结果一致。根据在不同入射能量下得到的一致结果和在392 MeV下发现的几个证据，可以得出结论，大部分的还原不是由核反应引起的，如多步效应。我们在相对论DWIA的schodenger等效形式中估计了核质量修饰的影响，发现大约一半的减少可以用这个模型解释，这再次与之前的392 MeV结果一致。我们已经知道，具有泡利阻挡效应的非相对论性计算不能再现所观察到的还原，而目前的结果，结合392 MeV的结果，支持了这种还原是强子水平上介质效应的一种表现的观点。少

It is predicted theoretically in the framework of QCD and QHD (quantum hadrodynamics) that hadron masses in nuclear field is modified as a result of partial restoration of chiral symmetry or as a representation of the lower-component enhancement of the nucleon Dirac spinor in a strong scalar field. At several hundred MeV of incident energies, the interactions between nucleons are well described by theoretical models based on the meson exchange forces. Thus it is expected that those mass modifications cause modification of NN interactions which is detectable in some nuclear reactions. And the nucleon quasifree scattering is expectable one of such reactions, since this reaction can be regarded as a NN scattering in nuclear field and suited for studying the NN interaction in nuclear field. It is first found by TRIUMP people that the analyzing power for a (p,2p) reaction leading to a 1s1/2-hole state shows distinct reduction from the free p-p scattering values. At RCNP, this reduction is s … More hown to be monotonically density-dependent, which suggests the existence of some medium effect. Such reduction has also been observed at 1 GeV for a 7Li target.In the present study, we have measured polarization for the (p,2p) reactions at 1 GeV at PNPI. The two-arm magnetic spectrometer system is employed for the measurement and a focal plane polarimeter which consists of a carbon analyzer and MWPC's is used on each spectrometer in order to measure the polarization of outgoing protons. We found that the data show strong density-dependent reductions from calculated values using the free NN interaction. This result is consistent with the 392 MeV result. From the fact that the consistent results are obtained at different incident energies and from several evidences found at 392 MeV, it is concluded that the most part of the reductions are not nuclear reaction originated, such as by a multi-step effect. We have estimated the effect of nucleon-mass modification in a Schodenger-equivalent form of the relativistic DWIA and found that about a half of the reduction is explained by this model, which is again consistent with previous 392 MeV result. It is already known that a nonrelativistic calculation with the Pauli blocking effect does not reproduce the observed reduction and the present result, in conjunction with the 392 MeV results, supports the idea that the reduction is a manifestation of a medium effect in the hadron level. Less