Study on Quark-Gluon-Plasma in the High Energy Heavy Ion Collision

本项目的最终目标是探测和研究夸克-胶子等离子体（QGP），这是一种高能高密度核物质的新阶段，预计将由高能重离子碰撞形成。作为核物质新相态研究的第一步，我们从测量重离子碰撞产生的介子、介子和质子的包容谱开始，这些碰撞的入射能量为14.5 GeV/核子。测量到的强子横向动能分布在测量区域内用指数形式描述得很好。在si诱导反应中，在1.1 ~ 1.5的快速区，质子的反斜率（斜率参数）大于介子的反斜率（斜率参数），而斜率参数既不取决于发射粒子的种类，也不取决于靶核的质量数。介子与介子的产率特别有趣，因为有几种理论预测这一比率将是QGP形成的一个很好的信号。在我们的测量中发现，在Si-Au碰撞中，正电介子和介子的比值为14.9%，负电介子和介子的比值为4.7%。在对旁观者效应进行校正后，上述比例在参与区域为正极粒子为8%，负极粒子为3%。尽管这些比率比p-p碰撞大1.5倍，但它们并不像QGP预测的比率那么大。然而，对这种影响的持续研究是必要的。除了这些强子测量外，我们还进行了计算机模拟，以研究检测电子-正电子对作为QGP形成信号的可能性。根据仿真结果，我们设计并构建了探测系统，并进行了电子-正电子对探测的测试实验。

Final goal of this research project is to detect and investigate a Quark-Gluon Plasma (QGP), a new phase of high-energy and high-density nuclear matter which is expected to be formed by the high energy heavy ion collisions. As a first step of this study of new phase of nuclear matter, we started from the measurements of the inclusive spectra of pions, kaons, and protons produced by the heavy ion collisions at the incident energy of 14.5 GeV/nucleon at BNL-AGS.The measured transverse kinetic energy distributions of hadrons are well described by an exponential form in the measured region. The inverse slope (slope parameter) for protons is found to be larger than that of pions at the rapidity region from 1.1 to 1.5 in Si-induced reactions, whereas the slope parameter depends neither on emitted particle species nor on mass number of target nuclei.The yield ratio of kaons to pions is especially interesting because several theories predict this ratio will be a good signal of the QGP formation. In our measurements this ratio was found to be 14.9 % for positive kaons and pions, and 4.7 % for negative kaons and pions in Si-Au collisions. After the corrections for the spectator effects, the above ratios in the participant region become 8% for positive particles and 3% for negative particles. Although these ratios are by a factor of 1.5 larger than in p-p collisions, they are not as large as the predicted ratios from the QGP. However, the continuous study of this effect will be necessary.Besides these hadron measurements, we did the computer simulations to study the possibility of detecting the electron-positron pair as a signal of the QGP formation. Considering the results of this simulation, we designed and constructed the detector systems and performed the test experiments for the detection of electron-positron pair.