Multiplicity fluctuation analysis of target residues in nucleus-emulsion collisions at a few hundred MeV/nucleon

Multiplicity fluctuation of the target evaporated fragments emitted in 290 MeV/u ¹²C-AgBr, 400 MeV/u ¹²C-AgBr, 400 MeV/u ²⁰Ne-AgBr and 500 MeV/u ⁵⁶Fe-AgBr interactions is investigated using the scaled factorial moment method in two-dimensional normal phase space and cumulative variable space, respectively. It is found that in normal phase space the scaled factorial moment (ln<F_q>) increases linearly with the increase of the divided number of phase space (lnM) for lower q-value and increases linearly with the increase of lnM, and then becomes saturated or decreased for a higher q-value. In cumulative variable space ln<F_q> decreases linearly with increase of lnM. This indicates that no evidence of non-statistical multiplicity fluctuation is observed in our data sets. So, any fluctuation indicated in the results of normal variable space analysis is totally caused by the non-uniformity of the single-particle density distribution.     

Multiplicity fluctuation analysis of target residues in nucleusemulsion collisions at a few hundred MeV/nucleon

Multiplicity fluctuation of the target evaporated fragments emitted in 290 MeV/u12C-AgBr, 400 MeV/u12C-AgBr, 400 MeV/u20Ne-AgBr and 500 MeV/u56Fe-AgBr interactions is investigated using the scaled factorial moment method in two-dimensional normal phase space and cumulative variable space, respectively. It is found that in normal phase space the scaled factorial moment(ln Fq) increases linearly with the increase of the divided number of phase space(lnM) for lower q-value and increases linearly with the increase of lnM, and then becomes saturated or decreased for a higher q-value. In cumulative variable space ln Fq decreases linearly with increase of lnM. This indicates that no evidence of non-statistical multiplicity fluctuation is observed in our data sets. So, any fluctuation indicated in the results of normal variable space analysis is totally caused by the non-uniformity of the single-particle density distribution.     

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     

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.     

Forward-backward multiplicity correlation in high energy hadron-hadron collisions

The forward-backward multiplicity correlation over the full pseudorapidity range forpp andp \(\bar p\) collisions at ISR and Collider energies have been analysed in terms of a Chou-Yang Type multiplicity distribution which consists of a stochastic (binomial) component forz=n _F ?n _B and a nonstochastic (negative binomial) component forn=n _F +n _B . Reasonable agreement with experimental data is obtained if the final-state particles are assumed, in a cluster model, to be created by the decay of clusters with a mean cluster size (charged particles per cluster) which is energy-dependent.     

Analysis of shower particle multiplicity in hadron-nucleus collisions in the few hundred GeV region

An analysis of relativistic charged secondaries produced in hadron-nucleus collisions in the few hundred GeV region is presented from the point of view of the structure of hadrons and to examine the possibility of discriminating different theoretical models. An attempt has been made to study the mean normalised multiplicity ratio in the central region and its dependence on the mean number of intranuclear collisionsv. The rate of increase in the production of particles exhibits good agreement with our proposed approach of the constituent supercluster model.     

Direct processes in heavy ion collisions at E ⩽ 20 MeV/u

Elastic and inelastic scattering at projectile energies of E ? 20 MeV/u have been studied using a magnetic spectrometer. It is shown that nuclear rainbow scattering for ¹²C + ¹²C allows to extract information from small inter nuclear distances. The role of the collective inelastic excitations is studied and it is shown that they lead to a decomposition of the projectile (or target)if the threshold for particle emission is close to the excitation energy of low lying collective states. The origin of the continuous background in the study of high lying excitations in nuclei is studied and it is shown that it can be analysed quantitatively.     

Light fragments produced in40Ar+natAg reactions at 27MeV/u

Angular and energy distributions have been measured for products of 4≦Z≦12 from reaction of 1,095 MeV⁴⁰Ar+^natAg. In addition to sources located near the projectile and fusion system velocities, the data show the presence of a source located aroundV _beam/2 which cannot be explained by any existing model. A possible interpretation is proposed.     

Charge correlations of fragments in heavy-ion collisions at Fermi energy

Fragments for oxygen and sulphur-induced reactions were measured at Fermi velocity. We study charge correlation functions. When the emission angles are outside the grazing angle no correlation is observed pointing to statistical emission. When one angle is within the grazing angle an enhanced correlation is detected due to inelastic break up of the projectile.     

Resonant electron transfer andL-shell excitation at 3.6 MeV/u Smq+→Xe collisions

Resonance energies and widths of four resonances in the reaction²⁵Mg(p,γ)²⁶Al were measured with the high resolution proton beam of the new 500 kV accelerator IONAS. The previously given large width of the 389 keV resonance, Γ= 460±70 eV. (1), used in the interpretation of stellar²⁶A1 production was shown to be incorrect and probably caused by target oxidation effects and insufficient energy resolution of the beam. The new value is Γ<4 eV.     

Neutron emission from 14N + 165Ho collisions at 35 MeV/u

Neutron emission from ¹⁴N + ¹⁶⁵Ho collisions has been studied at 25 MeV/u incident energy. Energy and angular distributions of the neutrons were measured in coincidence with projectile-like fragments (Li, Be, B, and C) emitted at angles of 10° and 30°. The spectra of neutrons at angles far from the angle of a coincident fragment have been satisfactorily parameterized in terms of a slowly moving, target-like source of temperature 2–3 MeV and a half-beam-velocity source of temperature about 7 MeV. The latter source accounts for about 20% of the detected neutrons for in-plane measurements. The out-of-plane cross sections are smaller. The relevant parameters of the moving-sources parametrization suggest a simple model which qualitatively explains the data in terms of the development of a hot participant zone and its subsequent mass exchange interactions with spectators in the projectile and target nuclei.     

High transverse momentum proton emission in Ar + Ta collisions at 94 MeV/u

Energy spectra of fast protons arising from Ar + Ta collisions at 94 MeV/u have been measured at large angles. These data are analysed in the framework of a one-body transport theory simulated by the BNV code. The low cross section measured for very energetic protons rules out a possible mechanism of kaon production via incoherent nucleon collisions at such low beam energies.     

Forward-backward multiplicity distribution in a two-component model

We calculate stochastic quantities in a two-component model which is a product of a negative binomial and a Poisson distribution. The generating function and the KNO scaling function are obtained. A formula for the forward-backward (F-B) multiplicity correlation is derived from the generating function. We consider the case in which particles are produced in pairs and compare with experiment.     

Forward-backward multiplicity correlations of pions and protons for different temperature events in heavy-ion interactions

A comparison of transverse momentum (P _T) distribution of the alpha particles emitted as projectile fragments from¹²C-emulsion interaction at 4.5 A GeV/c with double Maxwell-Boltzmann distribution yields two temperatures in the projectile fragmentation region, i.e., 10 MeV and 40 MeV with different reaction mechanisms, thereby giving rise to two classes of events. This work presents a detailed study of the multiplicity characteristics for pions and protons emitted in both forward and backward hemispheres in these two classes of events. The results show some interesting features in these two classes.     

High-energy fragments produced in the84Kr+93Nb reaction at 34.5 MeV/u

We have studied the heavy-ion capture reaction⁹Be(¹²C,γ)²¹ Ne at E_CM=3.5–6.6 MeV and Θ = 90. High-energyγ-rav decay to the low-lying states of²¹Ne was observed, even well below the Coulomb barrier.     

Light-particle emission versus evaporation residue formation in collisions of40Ar onnatCa at 30 MeV/u

The closely associated phenomena of preequilibrium emission and evaporation residue formation in fusion-like reactions were studied in central collisions between⁴⁰Ar and^natCa at 30 MeV/u. Heavy reaction products were taken in coincidence with neutrons and light charged particles. The preequilibrium neutron data agree very well with predictions of a quantal phase-space model which, in addition to the mean field, takes two-body collisions properly into account. Preequilibrium emission ends in thermally equilibrated hot nuclei with an average excitation energy of about 6 MeV/u. The combined results show a striking interrelation between the missing mass and light-particle multiplicities: the mass difference between the full compound mass and the observed residues can be explained quantitatively by the emission of only neutrons and light charged particles withZ2 during the entire course of energy dissipation.Supported by the German Bundesministerium für Forschung und Technologie (BMFT) under contract 06 HD 983I     

Particle emission in central nuclear collisions between48Ti und45Sc at 16 MeV/u

Protons and α-particles were measured in coincidence with fusion residues for the reaction⁴⁸Ti+⁴⁵Sc at 16 MeV/u beam energy. Their velocity distributions show a drastic broadening to higher as well as to lower velocities as compared to the calculated equilibrium emission pattern. This is interpreted as a kinematical effect of variations of the initial velocity of the emitting system, which are attributed to the preequilibrium emission of heavier clusters from the projectile or the target nucleus in incomplete fusion processes. The measured widths of the velocity distributions of the fusion residues are consistent with this mechanism. A peak in the product mass spectrum at masses between 6 and 18 is tentatively identified with the postulated cluster emission.     

Proton-proton correlations at small relative momentum in neon-nucleus collisions at E/A=400 and 800 MeV

Proton-proton small angle correlations have been measured in neon-nucleus collisions, using the 4 pi detector Diogene, at 400 and 800 MeV per nucleon incident energies. Values of the size of the emitting region are obtained by comparison with the Koonin formula, taking into account the biases of the apparatus. The dependence of the density on target mass and incident energy is also analysed.