Experimental study of high energy hadronic matter

我们组织了一个国际合作小组NA 44。NA 44在CERN-SPS上进行了重离子碰撞的单粒子和双粒子测量，积累了450 GeV质子、200 ACeV硫和160 AGeV铅的实验数据。特别是，铅束数据已采取的第一次在世界上，并为这种数据采取我们采用了一种新型的切伦科夫计数器（阈值成像切伦科夫）wihch已开发的欧洲核子研究中心广岛组。NA 44小组继续进行了数据处理和分析工作，发现了CERN SPS能区重离子碰撞产生的强子物质的许多有趣的特征。在横动量（P_T）分布方面，其他研究组报道了在低P_T和靶快度下的反常增强。但在低P_T和中等快度时仅发现小的增强。这种小的增强与共振产生的效果一致。(2)检测到了氘核和反氘核，验证了聚并模型的有效性。氘核和反氘核的相对生成速率似乎随P_2的增加而增加。(3)从HBT分析出发，确定了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（mT）的关系证实了流体动力学模型所预言的横向膨胀和流动的存在. (4)在国际上首次测定了理论上预期但实验上尚未观测到的π介子冻结时间分布宽度。观测值并不像QGP相变发生时所预期的那么大。(5)π介子和K介子的HBT参数都可用一个仅为m_T的函数来描述，而π介子和K介子的HBT参数之间的差别仅仅是由于它们的质量不同。

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.