Experimental Study on Quark-Gluon-Plasma at BNL

日美高能重离子对撞国际合作在美国布鲁克海文国家实验室AGS进行了高强度14.5 AGeV硅束实验和11 AGeV金束第一轮实验。实验的主要目标是：(1)研究介子和介子的两粒子相关性；(2)利用以磁谱仪为中心装置的实验系统，以良好的统计量测量很少产生的强子（即k和反质子）。通过双粒子相关测量可以研究核-核碰撞的时空演化。以前也进行过k -和反质子的测量试验，但由于统计量低，无法对它们的产生进行推断。为了实现这一目标，我们建立了一个特殊的触发系统，通过该系统可以在触发级上对粒子进行识别。严格的事件选择能力使高强度光束运行成为可能。两种粒子相关性的数据分析正在进行中，初步结果表明，用介子测量的源尺寸明显小于用介子测量的源尺寸。反质子产率与核物质中没有反质子吸收的模型计算结果一致，这与最初的预期有很大的矛盾。随着AGS-Booster的完成，重离子（Au）实验成为可能。我们可以期待在重离子的极端条件下研究不清物质的更好条件。第一个金束在1992年5月可用，我们有一个初步的短期运行。所得金束纯度大于99%。测量了横向和正向能量流。并尝试了用谱仪反向测量粒子光谱。数据分析正在进行中，新的覆盖前角区域的光谱仪正在建造中。

The experiment with high-intensity 14.5 AGeV Si-beams and the first-round experiment with 11 AGeV Au-beams have been carried out by the Japan-US international collaboration in high energy heavy ion collisions at the AGS, Brookhaven National Laboratory, USA.Primary goals of the experiment are (1) to study the two-particle correlations for pions and Kaons, and (2) to measure the rarely-produced hadrons (i.e. K-and anti-proton) with good statistics using the experimental system with a magnetic spectrometer as a central device.Space-time evolution of nucleus-nucleus collisions could be investigated through two-particle correlation measurement. Trial of measuring K-and anti-proton were made before, but low statistics prevented us to deduce any conclusions for their productions.In order to achieve the goals, we built a special trigger system by which particle identification in the trigger-level was made possible. Stringent event selection capability made it possible to run with high-intensity beams.Data analyses of two particle correlations are in progress, and preliminary result shows that source size measuremed by pions is significantly smaller than that measured by Kaons.Anti-proton yield was consisten with the model calculation with no anti-protons absorption in nuclear matter, which strongly contradicts to the naive expectation.With the completion of AGS-Booster, experiments with heavy ions up to Au became possible. We can expect a better condition to study unclear matter at extreme conditions with heavy ions. The first Au beam was available in May, 1992, and we had a prelminary short run. Purity of Au beam was better than 99%. Measurements of transverse and forward energy flow were made. Measurement of particle spectra at backward angle with spectrometer were also tried.Data analysis going on, and the construction of a new spectrometer which covers the forward angular region is in progress.