核子结构与高能pp反应过程中的自旋不对称
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摘要
随着人们对核子结构认识的深入,核子海夸克的自旋分布成为当前关注的重要前沿问题。特别是HERMES半单举轻子强子的深度非弹性散射实验给出的海夸克自旋分布与原来人们由单举深度非弹实验提取的结果很不相同,吸引了人们极大的兴趣。本文指出通过对纵向单极化高能pp反应过程中反超子的极化以及双极化过程中奇异粒子的双自旋不对称进行深入研究,可以为核子海夸克的自旋分布提供重要信息;并在因子化定理成立的框架内对RHIC能区这两类自旋不对称进行了系统地研究。
首先,我们给出了因子化定理成立时,单极化pp反应中反超子极化的一般计算公式,并系统分析了反超子极化时对各因子的依赖。然后,利用人们常用的蒙特卡罗事例产生器PYTHIA,计算了各种子过程对各种反超子产生的贡献。这些结果可以比较明显地告诉我们,一般情况下,参与硬碰过程的反海夸克碎裂是大横动量反超子产生的重要来源,并且反超子的产生率对核子内不同味道的海夸克分布依赖不同。然后,我们利用不同自旋模型的碎裂函数以及不同的海夸克自旋分布函数参数化做输入,系统地给出了各种反超子极化的数值结果。我们的这些结果清楚的表明:反超子的极化度对于碎裂过程的模型依赖并不强,而是对初态质子的海夸克的极化的部分子分布函数非常敏感。我们发现反超子(?)~0,反超子(?)~+以及反超子(?)对于质子海夸克中奇异夸克的极化分布非常敏感;反超子(?)~-以及反超子(?)~+会对轻味夸克的极化分布非常敏感。测量pp反应中的反超子极化提供给我们研究核子海奇异夸克极化分布的一个新的方法。这样,我们期望在RHIC实验中对反超子极化度的进一步测量能给出更多的关于核子中海夸克极化的信息。pp反应中双自旋不对称是极化的部分子分布函数的二次函数关系,一般比单极化的自旋不对称小很多。但由于此时不需测量末态粒子的极化,我们不仅可以研究超子反超子的产生过程,而且可以研究K介子等的产生过程。由于K介子产生率比反超子要高很多,实验统计性比较高,并且此时不涉及极化的碎裂函数,对研究核子内海夸克的自旋分布也比较有利。本文系统的研究了反超子(?),反超子(?)~+,反超子(?)~-,反超子(?)~0,反超子(?)~+以及K_0~S介子的不对称度。通过计算我们发现,类似于反超子的极化度,反超子(?)~0、反超子(?)~+以及反超子(?)对于质子海夸克中奇异夸克的极化分布非常敏感;反超子(?)~-以及反超子(?)+会对轻味夸克的极化分布非常敏感。
另外,我们还对RHIC能量下奇异粒子的产生的横向单极化不对称进行了模型计算,输出它们随x_F变化的数值结果,可以为将来进行的实验研究提供参考。
As people go deep into the nucleon's structure,the spin distribution of the nucleon sea became an attractively important frontier problem,especially when a semi-inclusive DIS precess measured by HERMES shows a contradicive result for the strangeness quarks distribution with all former experimental results gotten from inclusive DIS experiment.This interesting results attract people's attention.It is pointed out in this thesis that thorough investigation about antihyperon's polarization and double spin asymmetry of strangeness particles in high energy pp processes may provide important information about the spin distribution of the nucleon sea.Systematic studies have been carried out for those two spin asymmetry at RHIC energy within the framework of the factorization theorem.
Firstly,we presented the general formulae for antihyperon's polarization in singly polarized pp collision under the assumption that the factorization theorem is valid and calculation the dependence of the antihyperon's polarization on different factors.Then we use a well-known Monte-Carlo generator PYTHIA to calculate the fractional contribution of different subprocess to final antihyperon's production.The results demonstrate clearly that the sea quarks which experienced the parton level hard scattering,their fragmentation providing the dominance contribution to the antihyperon's production; meanwhile,the antihyperon's production ratio shows different flavor dependence on the nucleon sea.Then we adopting different spin related fragmentation functions and diverse polarized patton distribution functions as input and systematically delivered the numerical results of different antihyperon's polarization.Sensitivities have been found between the antihyperon's polar- ization and the polarization of the sea quarks' polarization,and the model dependent on the fragmentation process takes less effect.Specifically,(?)~0 and (?)~+ antihyperon's polarization is sensitive to the strange quarks' polarization of the initial nucleon;(?)~- and(?)~+ antihyperon's polarization is sensitive to the light flavor quark's polarization.Precise measurements about the antihyperon polarization in high energy pp process may provide us a new method to study the longitudinal polarized nucleon sea's structure.The double spin asymmetry of pp collision is the production of two polarized patton distribution functions,it should be generally small than the singly longitudinally asymmetry.However,as people do not need to measure the final particles' polarization,we can study the Kaon meson' ALL as well as those hyperon and antihyperon.As Kaon has high production ratio and high experimental statistics and it is not involved with polarized fragmentation function,study its double spin asymmetry will be helpful to understand nucleon sea quark's polarization.In this thesis,a detailed study for antihyperon's double spin asymmetry A_(LL) in pp collision with doubly longitudinally polarized beams have also been presented as well as for K_S~0 meson.Numerical analysis shows that similarly to result about the antihyperon's polarization,(?) antihyperon and A antihyperon's double spin asymmetry depend on the strange quarks' distribution of initial proton very much and(?) antihyperon's double spin asymmetry also shows sensitivity to the light flavor sea quark's distribution.
A model calculation for the strange particle's transversely single spin asymmetry have also been carried out at this thesis.Numerical results versus the kinematic variables such as Feymann-x scale will provide references for the future experimental investigation.
首先,我们给出了因子化定理成立时,单极化pp反应中反超子极化的一般计算公式,并系统分析了反超子极化时对各因子的依赖。然后,利用人们常用的蒙特卡罗事例产生器PYTHIA,计算了各种子过程对各种反超子产生的贡献。这些结果可以比较明显地告诉我们,一般情况下,参与硬碰过程的反海夸克碎裂是大横动量反超子产生的重要来源,并且反超子的产生率对核子内不同味道的海夸克分布依赖不同。然后,我们利用不同自旋模型的碎裂函数以及不同的海夸克自旋分布函数参数化做输入,系统地给出了各种反超子极化的数值结果。我们的这些结果清楚的表明:反超子的极化度对于碎裂过程的模型依赖并不强,而是对初态质子的海夸克的极化的部分子分布函数非常敏感。我们发现反超子(?)~0,反超子(?)~+以及反超子(?)对于质子海夸克中奇异夸克的极化分布非常敏感;反超子(?)~-以及反超子(?)~+会对轻味夸克的极化分布非常敏感。测量pp反应中的反超子极化提供给我们研究核子海奇异夸克极化分布的一个新的方法。这样,我们期望在RHIC实验中对反超子极化度的进一步测量能给出更多的关于核子中海夸克极化的信息。pp反应中双自旋不对称是极化的部分子分布函数的二次函数关系,一般比单极化的自旋不对称小很多。但由于此时不需测量末态粒子的极化,我们不仅可以研究超子反超子的产生过程,而且可以研究K介子等的产生过程。由于K介子产生率比反超子要高很多,实验统计性比较高,并且此时不涉及极化的碎裂函数,对研究核子内海夸克的自旋分布也比较有利。本文系统的研究了反超子(?),反超子(?)~+,反超子(?)~-,反超子(?)~0,反超子(?)~+以及K_0~S介子的不对称度。通过计算我们发现,类似于反超子的极化度,反超子(?)~0、反超子(?)~+以及反超子(?)对于质子海夸克中奇异夸克的极化分布非常敏感;反超子(?)~-以及反超子(?)+会对轻味夸克的极化分布非常敏感。
另外,我们还对RHIC能量下奇异粒子的产生的横向单极化不对称进行了模型计算,输出它们随x_F变化的数值结果,可以为将来进行的实验研究提供参考。
As people go deep into the nucleon's structure,the spin distribution of the nucleon sea became an attractively important frontier problem,especially when a semi-inclusive DIS precess measured by HERMES shows a contradicive result for the strangeness quarks distribution with all former experimental results gotten from inclusive DIS experiment.This interesting results attract people's attention.It is pointed out in this thesis that thorough investigation about antihyperon's polarization and double spin asymmetry of strangeness particles in high energy pp processes may provide important information about the spin distribution of the nucleon sea.Systematic studies have been carried out for those two spin asymmetry at RHIC energy within the framework of the factorization theorem.
Firstly,we presented the general formulae for antihyperon's polarization in singly polarized pp collision under the assumption that the factorization theorem is valid and calculation the dependence of the antihyperon's polarization on different factors.Then we use a well-known Monte-Carlo generator PYTHIA to calculate the fractional contribution of different subprocess to final antihyperon's production.The results demonstrate clearly that the sea quarks which experienced the parton level hard scattering,their fragmentation providing the dominance contribution to the antihyperon's production; meanwhile,the antihyperon's production ratio shows different flavor dependence on the nucleon sea.Then we adopting different spin related fragmentation functions and diverse polarized patton distribution functions as input and systematically delivered the numerical results of different antihyperon's polarization.Sensitivities have been found between the antihyperon's polar- ization and the polarization of the sea quarks' polarization,and the model dependent on the fragmentation process takes less effect.Specifically,(?)~0 and (?)~+ antihyperon's polarization is sensitive to the strange quarks' polarization of the initial nucleon;(?)~- and(?)~+ antihyperon's polarization is sensitive to the light flavor quark's polarization.Precise measurements about the antihyperon polarization in high energy pp process may provide us a new method to study the longitudinal polarized nucleon sea's structure.The double spin asymmetry of pp collision is the production of two polarized patton distribution functions,it should be generally small than the singly longitudinally asymmetry.However,as people do not need to measure the final particles' polarization,we can study the Kaon meson' ALL as well as those hyperon and antihyperon.As Kaon has high production ratio and high experimental statistics and it is not involved with polarized fragmentation function,study its double spin asymmetry will be helpful to understand nucleon sea quark's polarization.In this thesis,a detailed study for antihyperon's double spin asymmetry A_(LL) in pp collision with doubly longitudinally polarized beams have also been presented as well as for K_S~0 meson.Numerical analysis shows that similarly to result about the antihyperon's polarization,(?) antihyperon and A antihyperon's double spin asymmetry depend on the strange quarks' distribution of initial proton very much and(?) antihyperon's double spin asymmetry also shows sensitivity to the light flavor sea quark's distribution.
A model calculation for the strange particle's transversely single spin asymmetry have also been carried out at this thesis.Numerical results versus the kinematic variables such as Feymann-x scale will provide references for the future experimental investigation.
引文
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