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，即接近光速的重核（如金）的迎头碰撞。主要研究者是T. J. Humanic和M. A.俄亥俄州州立大学物理系的丽莎。这些实验的主要目标是获得证据，证明这种类型的碰撞产生了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）组成的新物质相的相变，称为夸克物质。这种相变已经被描述自然界中夸克和胶子行为的量子色动力学（QCD）所预言。到目前为止，QCD的预言与实验之间没有任何分歧，因此找到夸克物质将是对这一理论的一个重大考验。夸克物质是额外的兴趣，因为它被认为是宇宙大爆炸后几微秒的状态，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，因为有必要在核物质中创造一个非常密集和热的区域，以便开始这种相变。此外，由于重离子与质子的大小相比相对较大，因此碰撞在时间上延长了，希望允许系统有足够的时间达到平衡，以便夸克物质状态得到良好的发展。因此，为了研究这一现象，人们倾向于在最高能量下用最重的离子进行重离子碰撞。在本建议中，将在布鲁克海文国家实验室（BNL）的相对论重离子对撞机（RHIC）上研究金对金的重离子碰撞，并在日内瓦欧洲核子研究中心的大型强子对撞机（LHC）上研究铅对铅的碰撞。2000年夏天开始输送束流的RHIC是目前正在运行的最高能量重离子加速器。为了寻找夸克物质相变发生的标志，必须研究碰撞中产生的粒子的性质，例如可以检测到的每种类型的粒子动量和多重性（例如π介子，K介子，质子和更奇特的粒子）。这将在RHIC使用星星实验的大型接收探测器完成，它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，相互作用区域的物理尺寸（使用两粒子干涉测量法），碰撞中达到的温度（从粒子动量分布）和奇异粒子的产生，如奇异重子。此外，还将利用ALICE实验为在LHC上研究更高能级的Pb+Pb碰撞作准备。从2007年开始，LHC将提供比RHIC高30倍的质心能量，即宇宙射线能量。因此，夸克物质产生的能量依赖性可以被研究，还可以继续寻找尚未预测的现象。除了上述的智力价值外，这一建议在教育、技术和计算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，因此将为这些群体提供如何开展大型合作研究和一般问题解决技能的培训。参与粒子探测器开发和测试将增强新技术，可适应商业和政府用途。由于这项研究需要大规模的计算，以获取和分析数据的万亿次万亿字节的规模，新的方法在信息科学，如计算网格系统，将被开发，这可以提高计算能力的社会作为一个整体。

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.