高能反应中末态相互作用和衰变对超子极化的影响
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摘要
高能反应中自旋效应是研究强相互作用性质的重要手段。由于末态超子的极化实验上能很方便的利用其衰变产物的角分布来测量;超子极化在高能自旋物理的不同课题的研究中都有重要作用,超子极化己成为自旋物理中的一个重要研究方向。对它们的研究,可以为高能反应中强子产生机制和强子结构等提供重要信息。在所有这些研究中,高能反应实验观测到的必定是末态超子,与碰撞产生的直生超子有一定差别,必定受到如下两二个因素的影响:强子衰变和末态强子间相互作用。因此,利用超子极化研究强子产生机制时,都必须首先将这两个因素考虑进来。本文将研究这二个因素对末态超子极化的影响。
目前已有文献讨论过强子衰变过程对超子极化的影响,但这些文献中通常将衰变过程的极化转移因子取为一个常数。本文的分析表明弱衰变过程和电磁衰变过程的极化转移因子都应与超子动量有关。在计算母粒子静止系中包含极化关联的超子衰变角分布基础上,我们给出了和末态超子出射方向有关的衰变极化转移因子。计算结果表明极化转移因子对出射的角度有较强的依赖。
末态强子间的相互作用对超子极化也有较大的影响,特别是在高能重离子对撞中,产生出的强子数目众多,使该效应更加不可忽略。最近文献中提出的相对反应面法线方向超子极化的研究,使该效应的研究更具现实意义。由于末态强子中的主要成分是π介子,作为一个例子,本文着重考虑了末态πΛ散射对Λ超子极化的影响,并使用一个手征不变有效拉氏量模型计算这一过程的具有固定反应面的截面并给出解析结果。计算结果表明非极化的Λ超子将通过末态相互作用沿着反应面法线方向被极化。
Spin effect in high energy reactions is powerful tool to study the properties of strong interaction .Since the polarization of final-state hyperon can be measured easily through the angular distribution of its decay products in experiment, hyperon polarization is of the significance in many issues of the high energy spin physics, the study of hyperon polarization in high energy reactions has became one important aspect of spin physics. The study of hyperon polarization can provide important information about hadronization mechanism and the structure of hadron. In all study of this aspect, we can only measure final-state hyperon which is somewhat different with directly produced hyperon in colllisions in high energy reactions experiments. There are two factors contributing to the properties of the hyperon: hadron decay and final-state interaction. When we study hadronization mechanism through hyperon polarization, we must firstly consider about this two factors. This thesis will study them.At present, contributions to hyperon polarization derived from hadron decay have been argued, but in this argument decay polarization transfer factor is assumed as a constant usually. However, this thesis's analysis shows that spin transfer factor should depend on momentum of the hypron in both weak decay and electromagnetic decay. We derive decay spin transfer factor depending on moving direction of the final-state hyperon by calculating hyperon decay angular distribution including polarization correlation in mother-particle static frame system. The result shows that decay spin transfer factor strongly depend on moving direction of final-state hyperon.Contribution to hyperon polarization from interaction between final-state hadron is important, especially in high energy heavy-ion collisions, since the number of hadrons produced is very large, the effect can not be neglected much more. The study of hyperon polarization along the direction opposite to the reaction plane in the resent paper make the effect is much full of practical significance. Since final-state handron is composed of π meason mostly, for the sake of simplification, we focus on mainly
contributions to A hyperon polarization from final-state πA scattering in this thesis, and give analytic result after making use of effective chiral invariant Lagrangians to calculate cross section with fixed reaction plane. The result shows that initial-state unpolarized hyperon will be polarized along the direction opposite to the reaction plane through final-state interaction.
目前已有文献讨论过强子衰变过程对超子极化的影响,但这些文献中通常将衰变过程的极化转移因子取为一个常数。本文的分析表明弱衰变过程和电磁衰变过程的极化转移因子都应与超子动量有关。在计算母粒子静止系中包含极化关联的超子衰变角分布基础上,我们给出了和末态超子出射方向有关的衰变极化转移因子。计算结果表明极化转移因子对出射的角度有较强的依赖。
末态强子间的相互作用对超子极化也有较大的影响,特别是在高能重离子对撞中,产生出的强子数目众多,使该效应更加不可忽略。最近文献中提出的相对反应面法线方向超子极化的研究,使该效应的研究更具现实意义。由于末态强子中的主要成分是π介子,作为一个例子,本文着重考虑了末态πΛ散射对Λ超子极化的影响,并使用一个手征不变有效拉氏量模型计算这一过程的具有固定反应面的截面并给出解析结果。计算结果表明非极化的Λ超子将通过末态相互作用沿着反应面法线方向被极化。
Spin effect in high energy reactions is powerful tool to study the properties of strong interaction .Since the polarization of final-state hyperon can be measured easily through the angular distribution of its decay products in experiment, hyperon polarization is of the significance in many issues of the high energy spin physics, the study of hyperon polarization in high energy reactions has became one important aspect of spin physics. The study of hyperon polarization can provide important information about hadronization mechanism and the structure of hadron. In all study of this aspect, we can only measure final-state hyperon which is somewhat different with directly produced hyperon in colllisions in high energy reactions experiments. There are two factors contributing to the properties of the hyperon: hadron decay and final-state interaction. When we study hadronization mechanism through hyperon polarization, we must firstly consider about this two factors. This thesis will study them.At present, contributions to hyperon polarization derived from hadron decay have been argued, but in this argument decay polarization transfer factor is assumed as a constant usually. However, this thesis's analysis shows that spin transfer factor should depend on momentum of the hypron in both weak decay and electromagnetic decay. We derive decay spin transfer factor depending on moving direction of the final-state hyperon by calculating hyperon decay angular distribution including polarization correlation in mother-particle static frame system. The result shows that decay spin transfer factor strongly depend on moving direction of final-state hyperon.Contribution to hyperon polarization from interaction between final-state hadron is important, especially in high energy heavy-ion collisions, since the number of hadrons produced is very large, the effect can not be neglected much more. The study of hyperon polarization along the direction opposite to the reaction plane in the resent paper make the effect is much full of practical significance. Since final-state handron is composed of π meason mostly, for the sake of simplification, we focus on mainly
contributions to A hyperon polarization from final-state πA scattering in this thesis, and give analytic result after making use of effective chiral invariant Lagrangians to calculate cross section with fixed reaction plane. The result shows that initial-state unpolarized hyperon will be polarized along the direction opposite to the reaction plane through final-state interaction.
引文
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13 Y. Hama and T. Kodama, Phys. Rev. D48, 3116(1993).
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15 Xu Qing-hua, Liu Chun-xiu and Liang Zuo-tang, Phys. Rev. D65. 114008(2002).
16 Werner Hofmann, Ann. Rev. Nucl. Part. Sci 38, 279(1988).
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25 H. T. Coelho, T. K .Das, and M. R. Robilotta, Phys. Rev. C28,1812(1983)
26 P. J. Ellis and H. B. Tang, Phs. Rev. C56, 3363(1997).
2 G. K. Mallot Proc. of the 12th International Symposium on High-Energy Spin Physics World Scientific,Singapore, 1996.
3 A. Lesnik et al., Phys. Rev. Lett. 35,770(1975); and the references given there. G. Bunce et al., Phys. Rev. lett. 36,1113(1976).
4 See, e.g., P. R. Cameron it al., Phys. Rev. D32,3070(1985).
5 Liang Zuo-tang and C. Boros, Phys. Rev. Lett. 79,3608(1997).
6 For a recent review, see e.g., Liang Zuo-tang and C. Boros, Inter. J. Mod. Phys. A15, 927-982(2000).
7 HERMES Collaboration, A. Airapetian et al,Phys. Rev. Lett. 94(2005)012002,and the references given there.
8 B. Andersson, G. Gustafson, and G. Ingelman, Phys. Lett. B85,417(1979).
9 A. Bravar Proc. of the 13th International Symposium on High-Energy Spin Physics World Scientific,Singapore, 1998.
10 R.L.Jaffe, Phys. Rev. D54, R6581(1996).
11 C. Boros and Liang Zuo-tang, Phys. Rev. D57, 4491(1998).
12 Zuo-Tang Liang and Xin-Nian Wang, Phys. Rev. Lett. 94, 102301(2005).
13 Y. Hama and T. Kodama, Phys. Rev. D48, 3116(1993).
14 C. C. Barros and Y. Hama, Phys. Rev. C63, 065203(2001).
15 Xu Qing-hua, Liu Chun-xiu and Liang Zuo-tang, Phys. Rev. D65. 114008(2002).
16 Werner Hofmann, Ann. Rev. Nucl. Part. Sci 38, 279(1988).
17 T. D. Lee and C. N. Yang, Phys. Rev. 108,1645(1957).
18 G. Gustafson and J. H a kkinen, Phys. Lett. B303, 350(1993).
19 Paticle Data Group , D. E. Groom et al., Euro. Phys. J. C15, 1(2000).
20 R.Gatto, Phys. Rev. 109, 610(1957).
21 R. Stock et al., Proc. of the Conference on Quark Matter Formation and Heavy-ion Collisions, eds. M. Jacob and H. Satz. World Scientific,Singapore,1982.
22 A. D. Panagiotou, Phys. Rev. C33, (1986) 1999.
23 A. Y. Berdinkov et al., arXiv:nucl-th/0312045.
24 S. Weinberg, The Quantum Theory of Fields 2, Cambridge University Press, 1996.
25 H. T. Coelho, T. K .Das, and M. R. Robilotta, Phys. Rev. C28,1812(1983)
26 P. J. Ellis and H. B. Tang, Phs. Rev. C56, 3363(1997).