对夸克-胶子等离子体中粘滞系数和双轻子产生的研究

Relativistic heavy-ioncollisions mainly study the properties of nuclear matter under very hightemperature and energy density,searching for quark-gluon plasma(QGP).Dileptons havelarge mean free paths owing to the small cross section for electromagneticinteraction in the plasma; they therefore can provide an ideal probe for thedetection and study of the plasma.Many experiment results suggest that thebehavior of QGP can be described by dissipative hydrodynamics, with small shaervisosity.The viscosity of QGP is studied by many people in theoretical nuclearphysics. Recent calculationindicates that the bremsstrahlung processes gg<=>ggg are very important in the study of shear viscosity.In this work, we will study the shear viscosity of chemically equilibrating QGP at finite baryon density, including the contribution of elastic scattering as well as thebremsstrahlung processes of partons. By introducing viscous term into the QGP model, we will discuss the effect of shear viscosity on the evolution of temperature and chemical potential of QGP system. Based on this, we will calculate the dilepton production from quark annihilation, Compton-like scattering, multiple scattering of quarks and hot charms decay, and investigate the effect of shear viscosity on dilepton production.

相对论重离子碰撞主要是研究极端高温高能量密度条件下的核物质性质，寻找夸克-胶子等离子体。探测夸克-胶子等离子体的信号有很多，双轻子在离开碰撞形成的介质的过程中只有电磁相互作用，因此是研究QGP的良好探针。实验结果表明QGP的行为可以用耗散流体力学模型描述，具有较低的粘滞性。对QGP粘滞性的研究是当前理论核物理的一个热点。最近的理论研究表明胶子的非弹轫致辐射过程gg<=>ggg对剪切粘滞系数的贡献很大。本项目将研究具有有限重子数密度的化学平衡化QGP系统的剪切粘滞系数的大小，包括部分子弹性散射和轫致辐射等过程的贡献。通过在模型中引入粘滞性修正，探讨剪切粘滞系数对系统温度、化学势等演化的影响。在此基础上，全面考虑夸克对湮灭、类康普顿散射、多重散射和热粲夸克衰变等过程的双轻子产生，计算该QGP系统的双轻子谱并进一步探讨粘滞性对双轻子产生的影响。

相对论重离子碰撞主要目标是寻找夸克-胶子等离子，研究极端高温高能量密度条件下的核物质性质。本项目研究了夸克—胶子等离子体的剪切粘度系数，主要基于夸克弹性散射，胶子弹性和非弹性散射过程，利用动力学理论计算了化学平衡化、具有有限重子数密度的夸克-胶子等离子体系统的剪切粘滞系数及其与熵密度的比值，并研究了粘滞性对系统演化的影响。计算结果表明胶子非弹性散射过程的贡献很重要，粘滞性使得系统演化较理想系统变慢，而胶子非弹散过程使得系统演化的减缓程度较之前的计算结果有所变小。