Connecting Parton Cascade to QCDS Shear Viscosity for a Dynamical Model of Finite Temperature Kinetic Theory

在世界领先的加速器设施上进行的高能重离子碰撞实验，如美国的相对论重离子对撞机(RHIC)和欧洲的大型强子对撞机(LHC)，正在被用于研究高密度和高温度下极端状态物质的本构块。这类研究提供了关于大爆炸后宇宙性质的见解，当时胶子和夸克等基本粒子形成了被称为夸克胶子等离子体(QGP)或夸克汤的物质状态。这个项目将支持理论、模型和模拟的发展，以提高我们对QGP形成及其动力学性质的理解。该项目还将支持研究生和本科生的培训。在PI的指导下，学生将获得实用和分析技能，这些技能将为他们未来在学术界或行业的职业生涯提供良好的服务。PI和他们的学生开发的计算机代码是开源的，将为未来的研究提供一个实验平台，造福于核物理界。该项目的主要目标是将目前求解非线性相对论Boltzmann方程的ZPC Parton级联发展成有限温度QCD动力学理论的动力学模型。目前，ZPC只包括弹性散射，并以相同的双胶子散射截面处理所有口味。此外，它的截面在部分子演化过程中是由一个固定的屏蔽质量决定的，这导致了zpc ETa/S随温度的降低，这与pQCD或对现有实验数据的贝叶斯分析的结果相反。使屏蔽质量依赖于温度将导致ETa/S的正确的温度依赖关系，将包括前序非弹性部分子过程来描述化学平衡，并且与味道相关的截面将被用来适当地描述等离子体平衡。在确定了ETA和Parton截面之间的准确关系后，PI将调整屏蔽质量，以使Parton级联能够匹配预期的QCD剪切粘度，包括它对温度的依赖，直到QCD相变温度。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Experiments involving high-energy heavy-ion collisions at world-leading accelerator facilities such as the Relativistic Heavy Ion Collider (RHIC) in the U.S. and the Large Hadron Collider (LHC) in Europe, are being used to study the constitutive blocks of extreme states matter at high density and temperature. Such studies provide insights regarding the properties of the Universe right after the Big Bang, when elementary particles such as gluons and quarks formed a state of matter known as the quark gluon plasma (QGP) or quark soup. This project will support the development of theory, models and simulations needed to improve our understanding of the QGP formation and its dynamical properties. The project will also support the training of students at the graduate and undergraduate levels. Under the PI’s mentorship the students will acquire practical and analytical skills that will serve them well in their future careers in academia or industry. The computer codes developed by the PI and their students are open source and will provide a testbed for future research for the benefit of the nuclear physics community.The main goal of this project is to develop the current ZPC parton cascade, which solves the nonlinear relativistic Boltzmann equation, into a dynamical model of finite temperature QCD kinetic theory. Currently ZPC only includes elastic scatterings and treats all flavors with the same two-gluon scattering cross section. In addition, its cross section is determined by a fixed screening mass throughout the parton evolution; this leads to a decrease of the ZPC eta/s with temperature, contrary to the results from pQCD or the Bayesian analysis of available experimental data. Making the screening mass temperature-dependent will lead to the correct temperature-dependence of eta/s. Leading-order inelastic parton processes will be included to describe the chemical equilibration, and flavor-dependent cross sections will be used to properly describe the plasma equilibration. After a determination of the accurate relationship between eta and the parton cross sections, the PI will adjust the screening masses to enable the parton cascade to match the expected QCD shear viscosity including its temperature dependence down to the QCD phase transition temperature.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.