Experimental study of high energy hadronic matter

我们组织了一个国际合作小组NA44。NA44在CERN-SPS的重离子碰撞中进行了一次和两次粒子测量。积累了450 GeV质子、200A CeV硫和160A GeV铅的实验数据。特别是，铅束数据在世界上第一次被采集，对于这些数据，我们采用了一种新型的切伦科夫计数器（切伦科夫阈值成像），这是由欧洲核子研究中心广岛小组开发的。NA44小组一直在继续数据简化和分析工作，并发现了在CERN-SPS能量下重离子碰撞产生的强子物质的许多有趣特征。在横向动量（P_T）分布中，另一组在低P_T和靶速处报道了异常增强。然而，我们发现在低P_T和中快速时，只有很小的增强。这种小的增强与共振产生的效果是一致的。(2)检测了氘核和反氘核，并检验了聚结模型的有效性。氘核和反氘核的相对产率随P_2的增加而增加。(3)通过HBT分析，确定了介子和介子在高能重离子碰撞中产生的强子源的尺寸参数。这些参数与横向质量（m_T）的关系证实了水动力模型所预测的横向膨胀和流动的存在。(4)在国际上首次确定了理论预期而实验未观测到的介子冻出时间分布宽度。观测值并不像发生QGP相变时预期的那么大。(5)介子和介子的HBT参数都是由单个的m_T函数描述的，介子和介子的HBT参数的差异仅仅是由于它们的质量差异。

We have organized an international collaboration group NA44. The NA44 has carried out one and two particle measurement in heavy-ion collisions at the CERN-SPS.The experimental data with 450-GeV proton, 200A CeV sulphur and 160A GeV lead have been accumulated. In particular, the lead beam data have been taken for the first time in the world and for this data taking we employed a new type of Cherenkov counter (threshold imaging Cherenkov) wihch has been developed by the CERN-Hiroshima group. The NA44 group has been continuing the data reduction and analysis work and many interesting features have been found for the hadronic matter generated in heavy-ion collisions at the CERN-SPS energies. They are summarized as follows :In the transverse momentum (P_T) distribution other group has reported anomalous enhancement at low P_T and target rapidity. We have, however, found only small enhancement at low P_T and mid-rapidity. This small enhancement is consistent with the effect of resonance production.(2) Deuteron and anti-deuteron are detected and the validity of the coalescence model is examind. The relative production rate of deuteron and antideuteron production seems to increase as P_2 increases.(3) From the HBT analysis, the size parameters of hadronic source produced in high-energy heavy-ion collisions are determined for pion and kaon.The transverse mass (m_T) dependence of these parameters confirms the existence of the transverse expansion and flow which have been predicted by the hydro-dynamical model.(4) The width of pion-freezeout time distribution, which has been expected theoretically but not observed so far experimentally, is determined for the first time in the world. The observed values are not so large as expected from the occurence of QGP phase transition.(5) The HBT parameters for both pion and kaonare described by a single function of only m_T and the observed difference between those of pion and of kaon is simply due to their mass difference.