Relativistic Heavy Ion Collision Studies at RHIC and the LHC

这是一个由美国国家科学基金会资助的为期三年的项目，主要进行相对论重离子碰撞实验，即接近光速的重核（如金）的正面碰撞。主要研究者是俄亥俄州立大学物理系的t.j. Humanic和m.a. Lisa。这些实验的主要目标是获得证据，证明这种类型的碰撞会产生一种相变，从正常的核物质转变为一种由大量自由夸克和胶子（质子和中子的组成部分）组成的新物质，称为夸克物质。量子色动力学（QCD）预测了这种相变，量子色动力学是描述自然界中夸克和胶子行为的理论。到目前为止，量子cd的预测和实验之间还没有分歧，所以发现夸克物质将是对这一理论的主要检验。夸克物质更令人感兴趣，因为它被认为是大爆炸后几微秒的宇宙状态，今天可能存在于自然界中子星的中心。相对论性重离子碰撞可以提供一种在实验室中产生夸克物质的方法，因为为了开始这种相变，必须在核物质中创造一个非常密集和热的区域。此外，由于重离子相对于质子的大小要大一些，所以碰撞的时间被延长了，希望能让系统有足够的时间达到平衡，从而使夸克物质状态得到很好的发展。因此，为了研究这一现象，人们更倾向于在尽可能高的能量下与最重的离子进行重离子碰撞。在目前的提议中，重离子碰撞将在布鲁克海文国家实验室（BNL）的相对论重离子对撞机（RHIC）和日内瓦欧洲核子研究中心（CERN）的大型强子对撞机（LHC）上用金对金的碰撞进行研究。RHIC于2000年夏天开始发射粒子束，是目前投入运行的能量最高的重离子加速器。为了寻找已经发生了向夸克物质相变的特征，人们必须研究碰撞中产生的粒子的特性，例如粒子动量和每种类型的可检测的多样性（例如介子、介子、质子和更多的外来粒子）。这将在RHIC使用STAR实验的大型接收探测器完成，它可以对每次碰撞的大多数有趣粒子进行采样。以这种方式获得的信息可用于确定，例如，相互作用区域的物理大小（使用双粒子干涉测量法），碰撞中达到的温度（来自粒子动量分布）和异体粒子产生（如奇异重子）。此外，还将利用ALICE实验为在大型强子对撞机上研究更高能量的Pb+Pb碰撞做准备。从2007年开始，大型强子对撞机将提供比RHIC高30倍的质心能量，即宇宙射线能量。因此，可以研究夸克物质产生的能量依赖性，也可以寻求迄今为止无法预测的现象。除了上述智力上的优点外，这一建议在教育、技术和计算领域对社会产生了更广泛的影响。由于本科生、研究生和博士后研究人员将在该项目中发挥关键作用，因此将向这些小组提供如何开展大型合作研究和一般问题解决技能的培训。参与粒子探测器的开发和测试将提高新技术，这些新技术可以适应商业和政府的使用。由于这项研究需要大规模计算来获取和分析teraflop和tb规模的数据，因此将开发新的信息科学方法，如计算网格系统，以提高整个社会的计算能力。

This is a three-year program funded by the NSF primarily to carry outexperiments with relativistic heavy ion-collisions, i.e. head-oncollisions of heavy nuclei such as gold near the speed of light. Theprincipal investigators are T. J. Humanic and M. A. Lisa of theDepartment of Physics at The Ohio State University. The main goal ofthese experiments is to obtain evidence that collisions of this typeproduce a phase transition from normal nuclear matter into a new phaseof matter made up of a large volume of free quarks and gluons (theconstituents of protons and neutrons) called Quark Matter. This phasetransition has been predicted by quantum chromodynamics (QCD), which isthe theory that describes the behaviour of quarks and gluons in nature.Thus far, there have been no disagreements between the predictions ofQCD and experiment, so finding Quark Matter would be a major test ofthis theory. Quark matter is of additional interest since it is thoughtto have been the state of the universe several microseconds after theBig Bang and may exist today in nature at the centers of neutron stars.Relativistic heavy ion collisions could provide a method to produceQuark Matter in the laboratory since it is necessary to create a verydense and hot region within nuclear matter in order for the initiationof this phase transition. In addition, because heavy ions arerelatively large compared with the size of a proton the collision isextended in time, hopefully allowing the system enough time to reachequilibrium so that the Quark Matter state is well developed. Thus, tostudy this phenomenon one prefers heavy ion collisions at the highestpossible energies and with the heaviest ions available. In the presentproposal heavy ion collisions will be studied with gold on goldcollisions at the Relativistic Heavy Ion Collider (RHIC) at BrookhavenNational Laboratory (BNL) and lead on lead collisions at the LargeHadron Collider (LHC) at CERN in Geneva. RHIC, which started deliveringbeams in Summer 2000, is the highest energy heavy ion accelerator now inoperation. In order to look for signatures that a phase transition toQuark Matter has taken place, one must study the properties of theparticles produced in the collisions, such as particle momenta andmultiplicities of each type that can be detected (e.g. pions, kaons,protons, and more exotic particles). This will be done at RHIC using thelarge acceptance detectors of the STAR experiment, which can sample mostof the interesting particles per collision. The information obtained inthis way can be used to determine, for example, the physical size of theinteraction region (using two-particle interferometry), the temperaturesreached in the collisions (from particle momentum distributions) andexotic particle production such as strange baryons. In addition,preparations will be made to study Pb+Pb collisions at even higherenergies at the LHC with the ALICE experiment. The LHC will providebeams 30 times higher in center-of-mass energy than RHIC, i.e. cosmicray energies, starting in 2007. Thus, the energy dependence of QuarkMatter production can be studies and the search for as yet unpredictedphenomena can also be pursued.Besides the intellectual merit described above, there are broaderimpacts to society of this proposal in the areas of education,technology and computing. Since undergraduate students, graduatestudents and postdoctoral researchers will play key roles in thisproject, training will be provided to these groups in how to carry outresearch in large collaborations and in general problem solving skills.Participation in particle detector development and testing will enhancenew technologies which can be adapted to both commercial and governmentuse. Since this research requires large-scale computing in order toacquire and analyze data on the teraflop an terabyte scale, new methodsin information science, such as computing grid systems, will bedeveloped which can enhance the computing power of society as a whole.