Experimental study of quark gluon plasma with single photon measurement

2000年夏天，在RHIC上实现了Au核之间的碰撞，并开始了实验研究。本项目旨在确认夸克胶子等离子体（QGP）在RHIC的PHENIX实验中的实现，并研究QGP的性质。主要装置是一个电磁量热计，用来测量65个AGeV Au原子核碰撞时发射的光子。通过光子测量，可以确定中性介子的产率和光谱，最终目标是推导出单光子产率。构建了由高速网络连接的PC机和RAID盘组成的分析框架。高pT的中性介子主要是由粒子间散射产生的射流残留产生的。在碰撞初期，射流在高温下穿过物质时，由于强相互作用，能量损失较大。这个结果提供了喷气能量损失的第一个证据。单光子是QGP的探针，它直接提供来自QGP的信息。在假设由于胶子的贡献而快速热化的理论中，预测了大的光子产率。在本研究中没有观察到光子产率的大增强，这对模型有很强的限制。

In the summer of 2000, collisions between Au nuclei were realized at RHIC, and experimental studies have started. This project aims to confirm the realization of quark gluon plasma (QGP), and to study the properties of QGP, in the PHENIX experiment at RHIC. Primary device was a electro-magnetic calorimeter, in order to measure photons emitted from the collisions between 65 AGeV Au nuclei. With photon measurements, neutral pion yield and spectra would be determined and ultimate goal was to deduce single-photon yield. Analysis frame was constructed, which consists of PC's connected via high-speed network and RAID disks.Neutral pions with high pT are mainly produced as a residue of jets which are produced with the scattering between partons. Jet will suffer large energy loss due to strong interactions when it passes through the matter at high temperature in the initial stage of collisions. The result provided the first evidence of the jet energy-loss.Single photon is a probe of QGP, which directly provides information from the QGP. Large photon yield is predicted in the theory, which assumes fast thermalisation due to gluon contributions. Large enhancement in the photon yield was not observed in this study, which places strong restriction to the models.