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计划，主要是进行相对论重离子碰撞的实验，即在光速附近发生金等重核的迎头碰撞。主要研究人员是俄亥俄州立大学物理系的T.J.Human ic和M.A.Lisa。这些实验的主要目的是获得证据，证明这种类型的碰撞会产生从正常核物质到由大量自由夸克和胶子(质子和中子的成分)组成的新相物质的相变，称为夸克物质。量子色动力学(QCD)是描述夸克和胶子在自然界中行为的理论。到目前为止，QCD的预测与实验之间没有分歧，因此发现夸克物质将是对这一理论的重大考验。夸克物质引起了人们的额外兴趣，因为它被认为是大爆炸后几微秒内的宇宙状态，今天可能存在于自然界中的中子星中心。相对论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，因为为了启动这种相变，需要在核物质中创建一个密度非常高、非常热的区域。此外，由于重离子相对于质子的大小相对较大，碰撞在时间上被延长，有望使系统有足够的时间达到平衡，从而使夸克物质态得到很好的发展。因此，为了研究这一现象，人们倾向于在尽可能高的能量和可用的最重离子下进行重离子碰撞。在目前的方案中，将在布鲁克哈文国家实验室(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)上研究重离子与金的碰撞和铅与铅的碰撞。RHIC于2000年夏天开始交付束流，是目前运行中能量最高的重离子加速器。为了寻找相变到夸克物质已经发生的迹象，人们必须研究在碰撞中产生的粒子的性质，例如粒子动量和可以检测到的每种类型的多重性(例如，介子、介子、质子和更奇异的粒子)。这将在RHIC使用恒星实验的大型接受探测器来完成，该探测器可以在每次碰撞中对大多数感兴趣的粒子进行采样。以这种方式获得的信息可以用来确定，例如，相互作用区的物理大小(使用两粒子干涉测量法)，碰撞中达到的温度(根据粒子动量分布)和奇异粒子的产生，如奇异重子。此外，还将做好准备，利用Alice实验研究大型强子对撞机上甚至更高能量的铅-铅碰撞。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QuarkMatter生产对能源的依赖，也可以继续寻找尚未预测的现象。除了上述智力价值外，这一建议在教育、技术和计算机领域对社会有更广泛的影响。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，将向这些群体提供如何在大规模合作中开展研究和解决一般问题的技能的培训。参与粒子探测器的开发和测试将促进能够适应商业和政府用途的新技术。由于这项研究需要大规模的计算来获取和分析TB级的数据，因此信息科学中的新方法，如计算网格系统，将被开发出来，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.