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

原子核深处强子多体系统介质效应研究

• 批准号: 11694080
• 负责人: NORO Tetsuo
• 金额: $ 1.22万
• 依托单位: KYUSHU UNIVERSITY (2000-2001)Osaka University (1999)
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (B)
• 财政年份: 1999
• 资助国家: 日本
• 起止时间: 1999 至 2000
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-11694080/
• 关键词: QUASI-FREE SCATTERING; MEDIUM EFFECT; CHIRAL SYSMMETRY; RELATTVISTIC EFFECT; NUCLEAR REACTION; HADRON; INTERNATIONAL COLLABORATION; RUSSIA; 偏極; 磁気スペクトロメータ; 核子準弾性散乱; 核内ハドロン; 偏極分解能; 誘起偏極; 核相関; (p,2p)反応

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

在QCD和QHD(量子强子动力学)的框架下，理论上预言了核场中强子质量的改变是手征对称性部分恢复的结果，或者是强标量场中核子狄拉克旋量低分量增强的表现。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导致在某些核反应中可检测到的NN相互作用的修饰。由于核子准自由散射可以看作是核场中的NN散射，适合于研究核场中的NN相互作用，因此核子准自由散射是可以预期的反应之一。Triump等人首先发现，导致1s1/2空穴态的(p，2p)反应的分析能力明显低于自由p-p散射值。RCNP记者S…报道更倾向于单调依赖于密度，这表明存在某种媒介效应。对于7Li靶，在1GeV也观察到了这种还原。在本研究中，我们测量了PNPI在1GeV下(p，2p)反应的极化。测量采用双臂磁光谱仪系统，并在每个光谱仪上使用由碳分析器和MWPC组成的焦平面偏振器来测量出射质子的偏振。我们发现，与使用自由NN相互作用的计算值相比，数据显示出强烈的密度依赖的减少。这一结果与392 MeV的结果一致。根据在不同入射能量下获得一致结果的事实，以及在392 MeV处发现的几个证据，可以得出结论：大部分约化不是由核反应引起的，例如由多步效应引起的。我们在相对论DWIA的肖登格等价形式下估计了核子质量修正的影响，发现约一半的约化可以用这个模型来解释，这也与以前392 MeV的结果一致。已知，用泡利阻塞效应进行的非相对论计算不能重现观测到的约化现象，结合392 MeV的结果，支持这种约化是强子水平上介质效应的表现的观点。较少

项目成果

T.Noro et al.: "Spin Observables in Quasifree scattering"Proc.of RCNP-TMU Sympo.on Spins in Nucleear and Hadron Reactions(1999,Tokyo).

T.Noro 等人：“准自由散射中的自旋可观察量”Proc.of RCNP-TMU Sympo.on Spins in Nuclear and Hadron Reactions（1999，东京）。

T. Noro et al.: "Study of Nuclear Medium Effect on Hadrons in Nuclei by Nucleon Quasifree Scattering"Proceedings of International Nuclear Physics Conference. (2001)

T. Noro等人：“通过核子准自由散射研究核介质对原子核中强子的影响”国际核物理会议论文集。

T.Noro et al.: "NN Interaction and Nucleon and Meson Masses Studied with Nucleon Knockout Reactions"Proc.of PANIC99(1999,Uppsala). (to be published in Nucl.Phys.).

T.Noro 等人：“NN 相互作用以及核子和介子质量研究与核子敲除反应”Proc.of PANIC99（1999，乌普萨拉）。

T.Noro: "Nuclear Medium Effect Studied by Nucleon Quasifree Scattering ---A trial for study of nucleon and meson mass in nuclei---"Proceedings of 14th International Spin Physics Symposium (AIP Proceedings). 570. 228-237 (2001)

T.Noro：《核子准自由散射研究的核介质效应——原子核中核子和介子质量研究的试验——》第14届国际自旋物理研讨会论文集（AIP论文集）。

T. Noro et al.: "In-medium NN Interaction and Nucleon and Meson Masses Studied with Nucleon Knockout Reactions"Nuclear Physics. A663&664. 517c-520c (2000)

T. Noro 等人：“用核子敲除反应研究了介质中 NN 相互作用以及核子和介子质量”核物理。