Comparative study for nucleus-nucleus interactions and modified cascade evaporation model at (4.1 – 4.5) AGeV/c

The characteristics of the nucleus-nucleus collisions at high energy for the interactions of ¹H, ⁴He, ¹²C, ¹⁶O, ²²Ne, ²⁸Si and ³²S with emulsion at momentum (4.1 – 4.5) AGeV/c have been investigated. It has been found that the multiplicity distributions of the different emitted particles and their average values can be described by the modified cascade evaporation model. The model reproduces satisfactorily the multiplicity distributions of the shower, grey and black particles and the correlations between their multiplicities. It has been seen that the number of the produced shower particles increases with the increase of the projectile mass number. From the correlation between the average multiplicity of the evaporation particles and the number of the produced particles, it was found that a phase transition in the target system may occur. The calculated pseudo-rapidity distributions of the produced shower particles are typically Gaussian shaped in the mid-rapidity region and agree well with the experimental data. Also, the angular distributions of the grey and black particles have been investigated. The angular distributions of the grey particles show a universal shape independent of the type of projectile. The angular distributions of the black particles are nearly isotropic with a small asymmetry in the forward direction. The modified cascade evaporation model, reproduces the general characteristics of the nucleus-nucleus interactions and gives an explanation for the multiparticle production process.     

Multiplicity characteristics in relativistic 24Mg-nucleus collisions

This work is concerned with the analyses of the shower and gray particle production in 4.5 A GeV/c ²⁴Mg collision with emulsion nuclei. The highest particle production occurs in the region of the low impact parameters. While the multiplicity of the shower particles emitted in the forward direction depends on the projectile mass number and energy, the multiplicity of the backward ones shows a limiting behaviour. The source of the emission of the forward shower particles is completely different from that of the backward ones. The target fragments are produced in a thermalized system of emission.     

Multiplicity distributions of shower particles and target fragments in 7Li–Em collisions at 3 A GeV/c

Multiplicity distributions of shower particles and target fragments in ⁷Li–Em (emulsion) collisions at 3 A GeV/c are experimentally studied. In the framework of the multisource thermal model, the multicomponent Erlang distribution is used to describe the experimental multiplicity distributions of shower particles, grey fragments, black fragments, and heavily ionized fragments. The correlations between these multiplicities are experimentally reported. With the increase of impacting centrality (or the target fragment multiplicity), a saturation phenomenon for shower particle multiplicity is observed in the experiment.     

Forward–backward emission of target evaporated fragments in high energy nucleus–nucleus collisions

The multiplicity distribution, multiplicity moment, scaled variance, entropy and reduced entropy of target evaporated fragments emitted in forward and backward hemispheres in 12 A Ge V4 He, 3.7 A Ge V16 O,60 A Ge V16 O, 1.7 A Ge V84 Kr and 10.7 A Ge V197Au-induced emulsion heavy target(Ag Br) interactions are investigated. It is found that the multiplicity distribution of target evaporated fragments emitted in both forward and backward hemispheres can be fitted by a Gaussian distribution. The multiplicity moments of target evaporated particles emitted in the forward and backward hemispheres increase with the order of the moment q, and the secondorder multiplicity moment is energy independent over the entire energy range for all the interactions in the forward and backward hemisphere. The scaled variance, a direct measure of multiplicity fluctuations, is close to one for all the interactions, which indicate a correlation among the produced particles. The entropy of target evaporated fragments emitted in both forward and backward hemispheres are the same within experimental errors.     

290 AMeV 12C诱发乳胶核反应末态粒子多重数关联

对290 AMeV 12C诱发乳胶核反应末态粒子间的多重数关联进行了研究。实验结果表明:黑径迹粒子、灰径迹粒子、重电离粒子多重数之间存在较强的关联,而且黑径迹粒子和重电离粒子多重数有饱和的趋势,这些特征与高能区实验结果一致;簇射粒子与其他粒子间的关联性较弱,这一特征与高能区实验结果不同,主要归因于弹核能量较低、簇射粒子产额较小;黑径迹粒子、灰径迹粒子在前后半球的平均多重数随靶核的增大而增加;实验结果可用基于碰撞几何的旁观体-反应体模型及级联蒸发模型来解释。We have investigated the multiplicity correlation of particles produced in 12C-emulsion interactions at 290 AMeV. It is found that there is a strong correlation between black track particle, grey track particle and heavily ionized track particle, and finally black track particles and heavily ionized track particles tend to saturation, which is the same as the experimental results observed at high energies. The multiplicity correlation between shower particle and other particles is weaker, which is different from the experimental results observed at high energies. This discriminating character can be explained by the lower energy of projectile. The productivity of shower particle is lower at intermediate energies compared to that at high energies. The forward-backward averaged multiplicity of black track particle and grey track particle increases with the increasing target size.     

400 AMeV 12C诱发乳胶核反应重电离粒子前后关联研究

对400 AMeV 12C诱发乳胶核反应重电离粒子的前后关联进行了研究。重电离粒子来源于靶核碎片,分为灰径迹粒子和黑径迹粒子两种。实验结果很好地验证了核-核碰撞几何模型。灰径迹粒子的发射在前、后半球是各向异性的,而黑径迹粒子的发射基本是一致的。向前、向后发射的灰径迹粒子、黑径迹粒子平均多重数对重电离粒子数n_h呈线性依赖,黑径迹粒子、灰径迹粒子的向前发射随n_h的增加而增加的幅度分别大于其向后发射随n_h的增加而增加的幅度,但核内级联效应受靶核大小的影响,向后半球内发射的灰径迹粒子平均多重数随n_h的增加有饱和现象,这些多重数关联特性基本上可以利用基于碰撞几何的旁观体-反应体模型及级联蒸发模型来解释。The forward-backward multiplicity correlation of heavily ionized particles produced in 12C-emulsion interactions at 400 AMeV is investigated. The heavy ionized particles, come from the target fragments, are divided into grey track particle and black track particle. The experimental results can be well explained by the geometry model of the nucleus-nucleus collisions. The emission of grey track particles in forward and backward hemisphere is not isotropic, but the emission of black track particle is almost isotropic. The averaged multiplicity of grey track particles and black track particles in forward and backward hemisphere linearly depend on the number of heavily ionized particle n_h, the correlation strength in forward hemisphere is greater than that in backward hemisphere, but the dependence of grey track particle in backward hemisphere on the number of heavily ionized particle n_h shows the saturation because of the intranuclar cascade effect is influenced by target size. The characteristics of multiplicity correlations can be well explained by the participant-spectator model based on the colliding geometrical picture and the cascade evaporation model of high energy nucleus-nucleus collisions.     

几百兆电子伏特/核子能区原子核诱发乳胶核反应靶核蒸发碎片前后发射研究（英文）

对150 AMeV 4He-AgBr,290 AMeV 12C-AgBr,400 AMeV 12C-AgBr,400 AMeV 20Ne-AgBr及500 AMeV 56Fe-AgBr作用靶核蒸发碎片在反应前后半球内的多重数分布、多重数矩、标度方差、熵及约化熵分别进行了分析。实验结果表明,靶核蒸发碎片在前后半球内的多重数分布可以用高斯分布来描述。在前后半球内的多重数分布矩分别随秩数的增加而增加,且前后半球内多重数分布二阶矩与反应类型及束流能量无关。对于所有研究的核反应,其标度方差（一个直接描述多重数涨落的变量）值接近于1,表明在前后半球内靶核蒸发的发射存在较弱的关联。在前后半球内靶核蒸发碎片发射过程中的熵及约化熵在实验误差范围内与反应系统无关。The multiplicity distribution,multiplicity moment,scaled variance,entropy and reduced entropy of target evaporated fragments emitted in forward and backward hemispheres in 150 AMeV 4He-AgBr,290 AMeV 12C-AgBr,400 AMeV 12C-AgBr,400 AMeV 20Ne-AgBr and 500 AMeV 56Fe-AgBr interactions are investigated.It is found that the multiplicity distribution of target evaporated fragments emitted in both forward and backward hemispheres can be fitted by a Gaussian distribution.The multiplicity moments of target evaporated particles emitted in the forward and backward hemispheres increase with the order of the moment q,and the second-order multiplicity moment is energy independent over the entire energy range for all the interactions in the forward and backward hemisphere.The scaled variance,a direct measure of multiplicity fluctuations,is close to one for all the interactions,which indicate a weak correlation among the target evaporated fragments.The entropy of target evaporated fragments emitted in forward and backward hemispheres are the same respectively for all of the interactions,within experimental errors.     

4.5AGeV/c 24Mg与核乳胶碰撞中簇射粒子的赝快度分布

报道了4.5AGeV/c ²⁴Mg与核乳胶碰撞中产生的簇射粒子的赝快度分布,结果表明,分布宽度和峰值位置明显依赖于靶核尺寸.用柱模型对赝快度分布进行了分析,MonteCarlo方法计算得到的结果基本符合实验数据的走向,并重现了实验数据中的涨落现象.     

Self-affine multiplicity fluctuation of target residues in relativistic nuclear collisions at a few GeV to a few hundred GeV

Self-affine multiplicity scaling is investigated in the framework of two-dimensional factorial moment methodology using the concept of the Hurst exponent (H). Our investigation on experimental data of the target-evaporated slow particles emitted in ³²S-AgBr interactions at 200 AGeV and ²⁸Si-AgBr interactions at 14.5 AGeV reveals that a better power law behavior is exhibited in self-affine analysis than self-similar analysis. This work shows a clear evidence of self-affine target fragmentation. Received: 22 October 2001 / Accepted: 6 March 2002     

Pseudorapidity Distribution of Shower Particles in 24Mg-Emulsion Collisions at 4.5A GeV/c

The pseudorapidity distribution of shower particles produced in the ²⁴Mg-emulsion collisions at 4.5A GeV/c is reported in this paper. The dependences of the distribution width and the peak position on the target size are observed.The pseudorapidity distribution of shower particles for the events with low target multiplicity (light target) is narrower than that with high target multiplicity (heavy target). The maximum probability pseudorapidity for light target is greater than that for heavy target. The experimental data is analyzed by using the cylinder model suggested by Liu et al. The Monte Carlo results based on Liu's cylinder model are approximately in agreement with the experimental tendency and fluctuation.     

Characteristics of alpha projectile fragments emission in interaction of nuclei with emulsion

The properties of the relativistic alpha fragments produced in interactions of ⁸⁴Kr at around 1 A GeV in nuclear emulsion are investigated. The experimental results are compared with the similar results obtained from various projectiles with emulsion interactions at different energies. The total, partial nuclear cross-sections and production rates of alpha fragmentation channels in relativistic nucleus-nucleus collisions and their dependence on the mass number and initial energy of the incident projectile nucleus are investigated. The yields of multiple alpha fragments emitted from the interactions of projectile nuclei with the nuclei of light, medium and heavy target groups of emulsion-detector are discussed and they indicate that the projectile-breakup mechanism seems to be free from the target mass number. It is found that the multiplicity distributions of alpha fragments are well described by the Koba-Nielsen-Olesen (KNO) scaling presentation. The mean multiplicities of the freshly produced or newly created charged secondary particles, normally known as shower and secondary particles associated with target in the events where the emission of alpha fragments were accompanied by heavy projectile fragments having Z ≥ 3 seem to be constant as the alpha fragments multiplicity increases, and exhibit a behavior independent of the alpha fragments multiplicity.     

Systematic study of multiparticle production in nucleus–nucleus interactions at 14.6 A GeV

An experimental analysis of 855 events induced by 14.6 A GeV ²⁸Si in nuclear emulsion is presented. Mean multiplicities of charged secondary particles produced in the nuclear interactions are studied and compared with the results from the other experiments for the same projectile at 3.7 A GeV as well as data for proton at similar energy (14 GeV). An analysis of pseudorapidity densities of target fragments (black and grey particles) is also performed. The behaviour of the KNO scaling law of the multiplicity distribution for shower particles has been examined. In order to accumulate knowledge about the intermittent behaviour of shower particles, the scaled factorial moments (SFMs) are computed in η-space and ?-space for a set of data in the ²⁸Si–AgBr events. Furthermore, validity of limiting fragmentation of shower particles produced in central collision events induced by ²⁸Si-emulsion interactions has been tested. A crude estimation for the energy density of the nuclear matter formed in the central collision events at our energy has been examined.     

Evidence of self-affine multiplicity fluctuation of particle production in 84Kr--emulsion interactions at 1.7 A GeV

Self-affine multiplicity fluctuation is investigated by using the two-dimensional factorial moment methodology and the concept of the Hurst exponent (H). Investigation on the experimental data of compound particles and target fragments emitted in 84 Kr-AgBr interactions at 1.7 A GeV reveals that the best power law behaviours are exhibited at H=0.7 and 0.6 respectively, and the data for shower particles produced in 84 Kr-emulsion interactions at 1.7 A GeV indicate that the best power law behaviour occurs at H=0.6, all of which show the self-affine multiplicity fluctuation patterns. The multifractality and the non-thermal phase transition occurring during producing the compound particles, the target fragments, and the shower particles in the 84 Kr-AgBr interaction and the 84 Kr-emulsion interaction are also discussed. The multifractality is observed during producing compound particles, target fragments, and shower particles. In the target fragment production, an evidence of non-thermal phase transition is observed, but in the shower particle production and the compound particle production, no evidence of non-thermal phase transition is observed.     

Central events in the interactions of 28Si and 32S with heavy emulsion targets

Data on the multiplicity of secondaries in central events of ²⁸Si (14.6 AGeV) and ³²S (3.7 AGeV) interactions with AgBr emulsion nuclei have been compiled and studied. The dependence of the multiplicities of the outgoing charged stripping particles on the number of interacting nucleons and therefore on the impact parameter, as indicated by the target size, and consequently, on the degree of centrality is investigated. The resultant multiplicity distribution of the produced pions for each studied case is fitted by both Negative Binomial (NB) and Poisson distributions. The NB distribution is valid for most of the considered cases. The transparency of the target for a projectile was found to become more pronounced as the incident energy increased. Received: 20 June 2000 / Accepted: 17 January 2001     

Pion emission in α-particle interactions with various targets of nuclear emulsion detector

The behavior of relativistic hadron multiplicity for4He-nucleus interactions is investigated. The experiment is carried out at 2.1 A and 3.7 A Ge V(Dubna energy) to search for the incident energy effect on the interactions inside different emulsion target nuclei. Data are presented in terms of the number of emitted relativistic hadrons in both forward and backward angular zones. The dependence on the target size is presented. For this purpose the statistical events are discriminated into groups according to the interactions with H, CNO, Em, and Ag Br target nuclei. The separation of events, into the mentioned groups, is executed based on Glauber's multiple scattering theory approach. Features suggestive of a decay mechanism seem to be a characteristic of the backward emission of relativistic hadrons. The results strongly support the assumption that the relativistic hadrons may already be emitted during the de-excitation of the excited target nucleus, in a behavior like that of compound-nucleus disintegration.Regarding the limiting fragmentation hypothesis beyond 1 A Ge V, the target size is the main parameter affecting the backward production of the relativistic hadron. The incident energy is a principal factor responsible for the forward relativistic hadron production, implying that this system of particle production is a creation system. However, the target size is an effective parameter as well as the projectile size considering the geometrical concept regarded in the nuclear fireball model. The data are analyzed in the framework of the FRITIOF model.     

Pronounced Fluctuations of Target Fragments in Forward Hemisphere Only in Ultra Relativistic Nuclear Collision

Dynamical fluctuation of target evaporated black particles is investigated in both forward and backward hemispheres within the framework of multi-dimensional factorial moment methodology using the brilliant concept of the Hurst exponent. We analyse the black particles emitted in ^32S-AgBr interactions at 200AGeV and it is evident that the dynamical fluctuation in the backward hemisphere is self-affine. In the forward hemisphere, dynamical fluctuation is self-similar but not self-affine. However, study indicates that the fluctuation in the forward hemisphere is more pronounced than that in backward hemisphere.     

Projectile spectator proton production in 84Kr-emulsion interactions at 1.7 A GeV

The multiplicity distribution of projectile protons and multiplicity correlations between black particles, grey particles, shower particles, compound particles, heavily ionized track particles, projectile helium fragments and projectile spectator protons in <'84>Kr-emulsion collisions at 1.7 A GeV are investigated. It is found that the projectile spectator proton multiplicity distribution becomes broader with increasing target mass. The average multiplicity of shower particles and compound particles strongly depends on the number of projectile spectator protons, but the average multiplicity of black particles, grey particles and heavily ionized track particles weakly depends on the number of projectile spectator protons. The average multiplicity of projectile helium fragments increases linearly with increasing numbers of projectile spectator protons. Finally, the multiplicity distribution of projectile spectator protons obeys a KNO type of scaling law.     

Projectile spectator proton production in 84Kr- emulsion interactions at 1.7 A GeV

The multiplicity distribution of projectile protons and multiplicity correlations between black particles, grey particles, shower particles, compound particles, heavily ionized track particles, projectile helium fragments and projectile spectator protons in ⁸⁴Kr-emulsion collisions at 1.7 A GeV are investigated. It is found that the projectile spectator proton multiplicity distribution becomes broader with increasing target mass. The average multiplicity of shower particles and compound particles strongly depends on the number of projectile spectator protons, but the average multiplicity of black particles, grey particles and heavily ionized track particles weakly depends on the number of projectile spectator protons. The average multiplicity of projectile helium fragments increases linearly with increasing numbers of projectile spectator protons. Finally, the multiplicity distribution of projectile spectator protons obeys a KNO type of scaling law.     

Investigation of Multiplicity of Alpha-particle Interactions with Emulsion at 12A GeV

The multiplicity distribution of charged secondary particles and correlation between shower particles and heavy particles of alpha-particle interaction with nuclear emulsion at 12A GeV are discussed.The results indicate the mean multiplicity of heavy particle increase with shower particle numbers.