Square graphs in direct nuclear reactions at moderate energies

The present work contains the analysis of various reactions proceeding at relatively small projectile energies (～ 10 MeV) for which a mechanism described by the square diagram may be regarded as a dominant one. It is shown that such a mechanism may be realized both in reactions in which one or several nucleons are transferred and in reactions of nucleon or deutron inelastic scattering. Also, such an interesting property of the above diagrams is discussed as the extremely well pronounced forwardness of the angular distributions for the processes of inelastic scattering. Various variants of the theory are examined (DWBA, oscillator approximation, etc.). Formal properties of the square diagrams are also studied such as the dependence of differential cross section shape on the value of total orbital momentum transferred and the approximation on an energy surface for its calculation.     

氦泡生长实验数据的反演模拟计算方法

介绍了基于“迁移-合并”机理的氦泡生长理论模型与蒙特卡罗模拟方法，还研制了以上述算法为正算方式，对实验数据进行反演的迭代方法.最后应用这些方法对钯中氦泡生长实验数据进行了反演模拟计算，得到了氦泡半径与迁移速率的关系，并对计算结果作了分析.     

Analysis of fissionability data at high excitation energies

A level density formula that takes into account the smoothed volume, surface and curvature dependence of the single particle level density at the Fermi surface using the results of Balian and Bloch, is shown to be compatible with the level spacings found in neutron resonance data if complemented by a simple Ansatz for shell effects (due to Ignatyuk) and pairing effects. The three parameters involved, a scaling parameter, a shell damping energy and a pairing energy shift are compatible, respectively, with known nuclear radii, microscopic level density calculations and odd-even mass fluctuations. At excitation energies on the order of the neutron binding energy no evidence for an absolute level density problem or a different behaviour of level densities (collective contributions) for deformed nuclei as opposed to spherical nuclei is found. The proposed level density formula allows to calculate a priori macroscopic ratios of level densities, e.g. at the groundstate and at the saddle point, removing this important parameter from the analysis of fissionability data. As a first application, the fissionability of a number of actinide nuclei at excitation energies a few MeV above the fission barrier is analysed.     

Emission of heavy clusters in nuclear reactions at low collision energies

A survey of theoretical and experimental investigations of the process involving the emission of heavy clusters from excited nuclear systems produced in heavy-ion reactions at low collision energies is given. The dinuclear system (DNS) model for calculating cross sections for the formation of heavy clusters in complete-fusion and quasifission reactions is described in detail. The results of respective calculations are compared with relevant experimental data and with the results obtained on the basis of different models. The role of the angular momentum, the asymmetry of the entrance channel, the N/Z ratio, and the excitation energy in the formation of final reaction products is studied within the proposed approach. A method is developed for calculating cross sections for evaporation-residue formation. This method takes into account both channels of light-particle emission and channels of heavy-cluster emission. The possibility for the formation of Rn, Fr, and Ra isotopes in channels of heavy-cluster emission from the excited compound nucleus of Pu is demonstrated for the first time. The calculated cross sections and isotopic distributions for residual nuclei arising upon the emission of heavy clusters from an excited compound nucleus of Pu are in good agreement with experimental data. The model developed in the present study permits finding optimum experimental conditions (projectile-target combination and bombarding energy) for studying processes involving the emission of specific complex fragments.     

On the new possibility to describe the time evolution in nuclear collisions at high energies

In this work we give an attempt to introduce a temporal scale for nuclear collisions inspired by the Hubble cosmology and check it for Au+Au collisions at energies of 200 GeV/nucleon characteristic to BRAHMS Collaboration. We also give some correlations with different phenomena.     

A new space-time model for hadron-nucleus collisons at high energies

A new space-time model for hadron-nucleus collisions is proposed, where particles at the instant of creation are not only immature but their maturity rate is enhanced in the presence of other hadronic matter, as in a nucleus. With only one free parameter, the model can explain dn_A^p/dν, dn_A^π/dν, R_A^p(E_L), and the A-dependences of σ_in^pA and σ_in^πA.     

\gamma^* \gamma^* reactions at high energies

The total hadronic cross sections at high energy are calculated as a function of energy and photon virtuality in a model combining Reggeon exchange, the quark box diagram (a fixed pole in Regge language) and soft and hard pomeron exchanges evaluated in the context of dipole-dipole scattering. Good agreement is obtained with the data for the real cross section and for the real photon structure function . However the model prediction for the cross section is too small. This is attributed to an incorrect extrapolation of the dependence of the hard pomeron adopted here. Parametrising it independently shows that the hard part of the cross section can be well represented by a simple Regge pole with intercept . Received: 19 August 1999 / Published online: 3 February 2000     

Semi-hard parton rescatterings in nuclear collisions at very high energies

Representing the semi-hard partonic interactions by the exchange of Lipatov's perturbative Pomeron, we express the semi-hard nuclear cross section as a self shadowing cross section. With the help of a generating functional technique, we obtain average numbers of multiple semi-hard partonic collisions without any need of using explicit expressions for the multi-parton distributions. The average number of semi-hard interactions of a given projectile parton against a target nucleus is estimated quantitatively and it is shown to grow very rapidly above one with increasing the c.m. energy.     

An analysis of charge multiplicity data at high energies

The mode and the median charged multiplicities are both found to exhibit a similar increasing linear dependence on ln Q for pp, π^±p and K^±p interactions in the interval 1 < ln Q < 3(Q = available c.m. energy in GeV). The values obtained are compared to the predictions of the Nova model and the Chew-Pignotti model.     

A new transition radiator-detector system for particle identification at high energies

Transition radiation (TR) from a new low Z radiator of lithium foils was investigated with a xenon gas multiwire proportional chamber. The TR X-ray yield was determined as a function of the Lorentz factor from γ ≈ 1000 to 5600. The particle discrimination properties of the Li-radiator and Xe-detector combination were found superior to those reported with other TR detectors.     

QCD versus recent experimental data on lepton pair production at accelerator energies

New and precise experimental results on Drell-Yan pair production at accelerator energies are now available, both in π^? andp-nucleus interactions. These data are analyzed within the QCD framework including soft gluon resummation. It is shown that a quantitative agreement of the theory with experimental data can be reasonably managed. In particular, the soft gluon resummation is shown to build up nicely the so-calledK-factor. The pion formfactor is deduced from experimental data, but is rather sensitive to the nuclear structure functions we use. Definite nuclear structure functions are needed.     

A new contribution to deuteron screening at high energies

Effects arising from the structure of the Pomeron are shown to lead to a decrease in the apparent size of the Glauber screening correction to the π-d total cross section. This decrease is large enough to partially cancel effects arising from the usual inelastic intermediate state corrections to Glauber.     

Transverse energy flow in lepton and hadron induced reactions at high energies

We show that correlations betweenx- andy-components of the secondary particle momenta together with an amount of stochasticity and coherency account for the transverse energy (momentum) spectra observed recently in high energy collisions of leptons and hadrons. Relations obtained within the framework of quantum statistics involving the coherent state expansions are applied to e⁺e^– (at s 14 GeV), pp (26 GeV), ¯pp (900 GeV) and p + Au (200 GeV proton beam) collisions. The comparison of theoretical relations with data leads to sufficiently accurate conclusions. However, more experimental results of the same collision are needed as far as the values of the parameters involved should be determined uniquely.One of the authors (M. B.) acknowledges with pleasure the fruitful discussions with Drs. J. Peina, L. Kubáek, D. Krupa, J. Piút and M. Seman.     

Analysis of the π± p polarization data at high energies

The results of a phenomenological analysis are compared with the Regge model.     

Central nucleus-nucleus collisions at relativistic energies with a new method based on Random Matrix Theory

Using the method based on Random Matrix Theory (RMT),the results for the nearest-neighbor distributions obtained from the experimental data on 12C-C collisions at 4.2 AGeV/c have been discussed and compared with the simulated data on 12C-C collisions at 4.2 AGeV/c produced with the aid of the Dubna Cascade Model.The results show that the correlation of secondary particles decreases with an increasing number of charged particles Nch.These observed changes in the nearest-neighbor distributions of charged particles could be associated with the centrality variation of the collisions.     

Central nucleus-nucleus collisions at relativistic energies with a new method based on Random Matrix Theory

Using the method based on Random Matrix Theory （RMT）, the results for the nearest-neighbor distributions obtained from the experimental data on ^12C-C collisions at 4.2 AGeV/c have been discussed and compared with the simulated data on ^12C-C collisions at 4.2 AGeV/c produced with the aid of the Dubna Cascade Model. The results show that the correlation of secondary particles decreases with an increasing number of charged particles Nch. These observed changes in the nearest-neighbor distributions of charged particles could be associated with the centrality variation of the collisions.     

Diffractive dissociation on deuterons at high energies

It is shown that a study of the screening effect in the reaction p + d → X + d may yield important information about the space-time picture of high-energy hadron scattering. Arguments are given in support of the suggestion that in the parton picture of strong interactions the rescattering term in diffractive dissociation should be as large as in elastic scattering. The experimental data on the reaction p + d → X + d at energies higher than 100 GeV are analysed.