2π干涉学中的多π关联

多π事件中多π关联对2π干涉学的影响可以用相关π对取样中的多π关联因子和背景中剩余关联因子的比值来表示.在数据分析中这两种关联因子部分抵消,在π源半径较小,事件π多重数较大时,它们在小相对动量区域的差别变大,多π关联对2π干涉学结果的影响将变得重要.多π关联因子的分布C_n－2(q)能够敏感地反映事件中的多π关联效果.对Bevalac流光室2.1AGeV Ne+Pb和1.8AGeV Ar+Pb实验数据进行的多π关联因子分析表明,前者事件中的多π关联效果大于后者.     

相对论重离子碰撞中π对相对动量分布

在π源动量分布的高斯分布下,给出了相对论重离子碰撞中非关联π对和关联π对的相对动量分布.用关联π对的相对动量分布得到球形高斯分布π源参数与椭球形高斯分布π源参数的解析关系,与相对论重离子中心碰撞1.8A GeV Ar+Pb的实验结果进行了对比.当π源温度更高时,应当用p₁(p)=N·exp(–m2+p2/T)进行计算.     

计及多π关联效应的小相对动量区域2π干涉学

给出了相对论重离子碰撞中在关联nπ和非关联nπ的选取中存在多π关联效应时nπ关联函数的一般表达式.用这一表达式研究了计及多π关联效应的小相对动量区域2π干涉学,得到了从3π干涉学分析得到的π源参数与计及多π关联效应后,从2π干涉学分析得到的π源参数的解析关系,与相对论重离子中心碰撞1.?8A?GeV?Ar+?Pb的实验结果进行了对比.     

相对论重离子碰撞中π源密度分布和小相对动量区域2π干涉学分析

用2π关联函数在小相对动量区域的幂级数展开,得到了不同π源密度分布下源的空间参数、平均半径和均方根半径间关系,与相对论重离子中心碰撞1.8A GeV Ar+Pb的实验结果一致. 给出了上述反应中π源的平均半径和均方根半径.对不同的源密度分布,计算了K_t的值.     

多π关联对π发射源相干性的分析

对高能重离子碰撞中不同相于性程度π源产生的多π关联事件进行了蒙特卡罗模拟,比较了不同多重数子事件中的多π关联对π源相于性程度依赖的敏感性.对Bevalac流光室2.1A GeV Ne+Pb和1.2A GeV Ar+KCl中心碰撞产生的π源的相干性程度进行了分析,并与以往的2π干涉学的结果进行了比较.     

相对论重离子碰撞中小相对动量区域3π干涉学分析

用3π关联函数在小相对动量区域的幂级数展开,得到了3π关联函数与π源均方根半径的关系．对π源密度的高斯分布,在不考虑和考虑3π事件中的多π关联效应两种情况下,解析地得到了由2π干涉学分析得到的π源空间参数和由3π干涉学分析得到的π源空间参数的理论关系.计算了3π事件中的多π关联引起的2π关联因子的偏离.与小相对动量区域2π干涉学得到的结果和相对论重离子中心碰撞1.8A GeV Ar+Pb的实验结果进行了对比.     

非静态球形夸克-胶子等离子体的2π干涉学的检测

提出了一种相对论重离子碰撞中强子物质生成时的π膨胀源模型. 得到了该模型中的小相对论动量区域的2π关联函数及表观π源参数R_a与实际π源参数R_e的关系. 这一关系与QGP生成时的关系有所区别. 这一区别可以用来检测相对论重离子碰撞中产生的非静态球形夸克-胶子等离子体的存在性. 两个关系也显示了一种标度行为.     

计及多π关联效应的小相对动量区载2π干涉学

给出了相对重离子碰撞中的在关联nπ和非关联nπ的选取中存在多π关联效应时nπ关联函数的一般表达式。用这一表达式研究了计及多π关联效应的小相对动量区域2π干涉学,得到了从3π干涉学分析得到的π源参数与计及多π关联效应后,从2π干涉学分析得到的π源参数的角析关系,与相以论重离子中心磁撞1.8A GeV Ar Pb的实验结果进行了对比。     

2π干涉学分析的源空间参数

本文通过直接比较相应于不同密度分布源的关联函数,指出源的平均半径是2π干涉学分析中描述源空间线度的好物理量.比较不同关联函数分析获得的源空间参量时,选取源的平均半径为判别标准不仅优于Bartke和Kowalski提出的均方根半径,也优于Goldhaber等人提出的GGLP因子.对不同碰撞实验的2π干涉学结果的系统分析表明,使用我们提出的比较标准给出的结果更加合理.     

部分相干源关联函数的模拟计算

核-核碰撞可以简单看成核子-核子碰撞,每一核子-核子碰撞产生的源可用经典流表示。对于时空函数的经典流系综,当源部分相干时,全同两粒子玻色-爱因斯坦关联函数公式应包含混沌和相干项。根据蒙特卡罗的模拟计算思想,由混沌源2π关联函数的模拟计算出发,得到部分相干源关联函数的模拟计算方法。在相对动量q的out和side方向上,对部分相干源关联函数进行蒙特卡罗模拟计算,计算得到源的半径Rout在误差范围内近似等于Rside。     

Bose-Einstein correlations of three charged pions in hadronic Z^{\bf 0} decays

Bose-Einstein Correlations (BEC) of three identical charged pions were studied in hadronic decays recorded with the OPAL detector at LEP. The genuine three-pion correlations, corrected for the Coulomb effect, were separated from the known two-pion correlations by a new subtraction procedure. A significant genuine three-pion BEC enhancement near threshold was observed having an emitter source radius of and a strength of . The Coulomb correction was found to increase the value by 9% and to reduce by 6%. The measured corresponds to a value of when one takes into account the three-pion sample purity. A relation between the two-pion and the three-pion source parameters is discussed. Received: 7 May 1998 / Published online: 12 August 1998     

Effects of source opacity and expansion on two-pion Bose-Einstein correlations

We examine two-pion Bose-Einstein correlations for partially coherent particle-emitting sources within quantum statistical formalism, where the sources are treated as classical currents with chaotic and coherent components. The two-pion correlation functions of the partially coherent sources contain a phase which is sensitive to the asymmetry of the source emission function. We investigate the influence of source opacity and expansion in high energy heavy ion collisions on the phase by Monte Carlo calculati...     

Multi-pion Bose-Einstein correlation effects on three-pion interferometry

Multi-pion correlations effect on three-pion interferometry is studied. It is shown that multi-pion correlations decrease both the apparent radius of the source and the coherent source parameter derived from three-pion interferometry. The data of OPAL group are discussed.     

Source parameters deduced from Bose-Einstein correlations of two and three soft pions in symmetric heavy-ion interactions at 650 A MeV

The analysis of Bose-Einstein correlations for systems of two and three low-momentum pions in interactions of Au+Au and Nb+Nb at 650 A MeV kinetic energy are presented. The data were taken with the Plastic Ball spectrometer. The pion-emitting source sizes obtained from specific three-pion correlations are significantly smaller than those extracted from two-pion correlations. The dependence of the source parameters on the multiplicity of produced pions was examined. The low-p _t pions are emitted from a larger region than the high-p _t ones.     

Two-pion interferometry for granular sources

A review on the two-pion Hanbury-Brown—Twiss (HBT) interferometry in the granular source model of quark-gluon plasma droplets is presented. The characteristic quantities of the granular source extracted by imaging analysis are presented and compared with the HBT radii obtained by the usual Gaussian formula fit. The signals of granular sources are presented.     

Two-pion interferometry for a partially coherent evolution source

We give the formulas of two-pion Hanbury-Brown-Twiss (HBT) correlation function for a partially coherent evolution pion-emitting source, using quantum probability amplitudes in a path-integral formalism. The multiple scattering of the particles in the source is taken into consideration based on Glauber scattering theory. Two-pion interferometry with effects of the multiple scattering and source collective expansion is examined for a partially coherent source of hadronic gas with a finite baryon density and evolving hydrodynamically. We do not find observable effect of either the multiple scattering or the source collective expansion on HBT chaotic parameter.     

Note on Bose-Einstein correlations of three pions in symmetric heavy-ion interactions at 650 a MeV

In a recent article published in this journal it is stated that a specific three-pion effect is found in an experiment studying Au+Au collisions. The aim of this note is to show that these new data are compatible with two-pion effects leaving no room for a specific three-pion effect. This is in accordance with three-pion interferometry results from pp and e⁺ e^? collisions at a high energy.     

Three-pion correlations for studying partial coherence in nuclear collisions

Use of three-particle correlations provides a unique tool for studying partial coherence in relativistic heavy-ion collisions. Here a theory is presented for multiple coherent source components of partially coherent pion radiation. Results are given for the relative probabilities of emission of one, two, or three pions. The calculations on the relation between two- and three-pion correlators give some evidence, when compared with available experimental data, for the existence of partial coherence and multiple coherent components in heavy-ion collisions.     

Role of Δ exchange for p annihilation into two-pion and three-pion channels

p annihilation into two pions and three pions is studied in a baryon exchange model. Annihilation diagrams involving nucleon as well as Δ-resonance exchanges are included consistently in the two- and three-pion channels. Effects from the initial-state interaction are fully taken into account. A comparison of the influence of the Δ exchange on the considered annihilation channels is made and reveals that its importance for three-pion annihilation is strongly reduced as compared to two-pion annihilation. It is found that annihilation into three uncorrelated pions can yield up to 10% of the total experimentally observed three-pion annihilation cross-section. Received: 16 January 2002 / Accepted: 20 February 2002     

Two-pion interferometry for a partially coherent evolution source

We give the formulas of two-pion Hanbury-Brown-Twiss (HBT) correlation function for a partially coherent evolution pion-emitting source,using quantum probability amplitudes in a path-integral formalism.The multiple scattering of the particles in the source is taken into consideration based on Glauber scattering theory.Two-pion interferometry with effects of the multiple scattering and source collective expansion is examined for a partially coherent source of hadronic gas with a finite baryon density and evolving hydrodynamically.We do not find observable effect of either the multiple scattering or the source collective expansion on HBT chaotic parameter.