Relativistic Heavy-Ion Physics at the University of Rochester

这笔拨款为罗彻斯特大学物理与天文学系的相对论重离子小组提供运营资金。在这一年中，我们将完成对布鲁克海文国家实验室（BNL）相对论重离子对撞机（RHIC）上的PHOBOS探测器在2001年和2003年收集的数据的分析，并考虑PHOBOS探测器的可能升级方案。PHOBOS是四个实验之一，旨在观察原子核在RHIC碰撞时产生的极端能量密度。据信，一种新的物质状态，即所谓的夸克-胶子等离子体（QGP），将在这些碰撞中形成。PHOBOS正在寻找这种新的物质状态，它的性质将提供关于极早期宇宙状态（大爆炸后几微秒）的重要新信息。PHOBOS的设计目的是以无偏倚的方式研究尽可能多的碰撞，并寻找p+p、p+A和A+A碰撞之间的显著差异。到目前为止收集的数据包括2001年Au+Au碰撞，2003年d+Au碰撞，2001年和2003年p+p碰撞。预计QGP只会在Au+Au碰撞中形成，并且使用d+Au和p+p的研究来从Au+Au碰撞中收集的数据中减去“正常”核子-核子物理的贡献。由Rochester团队设计和建造的飞行时间阵列，将PHOBOS的粒子识别能力提高了一倍，大大提高了PHOBOS的物理能力。在2003年的运行中，我们增加了阵列的飞行路径，允许使用识别高达动量约4 - 5 GeV/c的粒子。2001年数据的分析基本完成，2003年数据的分析才刚刚开始。

This grant provides operating funds for the relativistic heavy-ion group at the Department of Physics and Astronomy at the University of Rochester. During the year covered by this grant we will complete the analysis of the data collected in 2001 and 2003 with the PHOBOS detector at the Relativistic Heavy-Ion Collider (RHIC) at Brookhaven National Laboratory (BNL) and consider possible upgrade options for the PHOBOS detector. PHOBOS is one of the four experiments looking at the extreme energy densities that are created when nuclei collide at RHIC. It is believed that a new state of matter, the so-called quark-gluon plasma (QGP), will be formed in these collisions. PHOBOS is looking for this new state of matter, and its properties will provide important and new information about the state of the very early universe (a few microseconds after the Big Bang). PHOBOS was designed to study as many collisions as possible, in an unbiased way, and to search for significant differences between p+p, p+A, and A+A collisions. The data collected sofar inlcudes studies of Au+Au collisions in 2001, d+Au in 2003, and p+p in 2001 and 2003. It is expected that the QGP will only be formed in the Au+Au collisions, and the studies of d+Au and p+p are used to subtract the contribution of "normal" nucleon-nucleon physics from the data collected in Au+Au collisions. The time-of-flight array, designed and constructed by the Rochester group, significantly enhances the physics capabilities of PHOBOS, by roughly doubling its particle identification capabilities. For the 2003 run we have increased the flight path of our arrays, allowing use to identify particles up to momenta of around 4 - 5 GeV/c. The analysis of the 2001 data is almost completed, and the analysis of the 2003 data is just getting started.