Microscopic theory of pion production and sidewards flow in heavy-ion collisions.
Microscopic theory of pion production and sidewards flow in heavy-ion collisions.
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DOI：
10.1103/physrevlett.54.289
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发表时间：
1985-01
影响因子：
8.6
通讯作者：
Kruse;Jacak;Stöcker
中科院分区：
文献类型：
--
作者：
Kruse;Jacak;Stöcker
以Vlasov自洽平均场和遵从泡利原理的Uehling-Uhlenbeck二体碰撞项为基础，用微观理论研究了0.3 ~ 2gev核子的核碰撞。该理论同时解释了观测到的集体流和介子多重性，并给出了它们对核状态方程的依赖关系。PACS数字：25.70。研究相对论性核-核碰撞最吸引人的动机之一是在实验室中探索压缩和激发核物质的独特机会。压缩的一个特征是核流体动力学和经典微观多体模拟理论预测的集体侧向流动。最近，在高重n~clei的多重选择碰撞中观察到预测的集体侧向流动。流体动力学预测的另一个可观测到的压缩效应是介子多重度与高密度核压缩能的依赖关系。~测量了Ar （0.3 ~ 1.8 GeV/核子）+ KCI近中心碰撞的介子数。这两组数据都对微观理论提出了挑战：流动计算是用标准的核内级联pr完成的。~的结果是前峰角分布，与数据相反。计算出的介子寿命大大高估了实验产率。考虑到级联模型在描述包容性数据方面的成功，这些巨大的差异令人惊讶。据推测，测量到的介子产量与级联预测之间的差异是由于在级联方法中忽略了压缩能，因此可以用来提取高密度下的核状态方程。在这封信中，我们提出了一个微观理论，第一次同时解释了观察到的集体流和介子多重性，并给出了它们对核状态方程的依赖。我们的方法是基于Vlasov在自洽平均势场中无碰撞等离子体的单粒子分布函数f的演化方程，并补充了UehlingUhlenbeck对玻尔兹曼二体碰撞项的量子力学扩展，该扩展遵循泡利原理。这个扩展的玻尔兹曼方程可以写成。Vlasov方程是通过对15个Ap+ AT测试粒子的平行系综经典运动方程的同时数值积分来求解的，这些粒子最初被赋予费米动量和在核半径球体中的随机位置。在每个同步时间步，计算每个测试粒子周围六维球面上的集合平均相空间密度。这一集合保证了一个相当平滑的单粒子分布函数f (r,p,r)，用于确定平均场U(n)和泡利阻塞概率（1 -,f） （1 -,f）。我
Nuclear collisions from 0.3 to 2 GeVInucleon are studied in a microscopic theory based on Vlasov's self-consistent mean field and Uehling-Uhlenbeck's two-body collision term which respects the Pauli principle. The theory explains simultaneously the observed collective flow and the pion multiplicity and gives their dependence on the nuclear equation of state. PACS numbers: 25.70.-z One of the most intriguing motivations for studying relativistic nucleus-nucleus collisions is the unique opportunity to explore compressed and excited nuclear matter in the laboratory. A signature of compression is the collective sidewards flow predicted theoretically by nuclear fluid dynamics' and classical microscopic many-body simu~ations.~ Recently, the predicted collective sidewards flow has been observed in highmultiplicity selected collisions of heavy n~clei.~,~ Another observable compression effect predicted by fluid dynamics is the dependence of the pion multiplicity on the nuclear compression energy at high densitie~.~ The pion multiplicities have been measured for near-central collisions of Ar (0.3-1.8 GeV/nucleon) + KCI.~ Both data sets present a challenge to microscopic theories: The flow calculationsL4 done with the standard intranuclear-cascade pr~~rams'.~ result in forward-peaked angular distributions, in contrast to the data. and the calculated pion m~lti~licities~- ~ drastical- I ly overestimate the experimental yields. These large discrepancies are surprising in view of the success of the cascade model in describing inclusive data.'j8 It has been conjectured6 that the difference between measured pion yields and cascade predictions is due to the neglect of compression energy in the cascade approach and thus may be used to extract the nuclear equation of state at high densities. In this Letter we present a microscopic theory which explains for the first time simultaneously both the observed collective flow and the pion multiplicity and gives their dependence on the nuclear equation of state. Our approach is based on Vlasov's equation for the evolution of the single-particle distribution function f of a collisionless plasma in a self-consistent mean potential field supplemented by UehlingUhlenbeck's quantum mechanical extension of Boltzmann's two-body collision term which respects the Pauli principle. This extended Boltzmann equation can be ~ritten~.'~ The Vlasov equation is solved by simultaneous numerical integration of the classical equations of motion of fifteen parallel ensembles of Ap+ AT test particles, which are initially assigned Fermi momenta and random positions in a sphere of nuclear radiiis. The ensemble-averaged phase-space density is computed at each synchronization time step in a six-dimensional sphere around each test particle. This ensemble a~eraging~,'~ ensures a reasonably smooth singleparticle distribution function f (r,p,r) which is used to determine the mean field U( n) and the Pauli-blocking probability ( 1 - ,f) ( 1 -,f). I