A new model in high energy collisions

In this work a hydrodynamical model is presented in order to explain physical phenomena appearing in nucleus-nucleus collisions. The model is based on a shock wave propagation in the fluid nuclear matter. The Burger- de Vries equation of shock waves is treated in the framework of mathematical topology. Experimental data for five pairs of nuclei is used in order to demonstrate the viability of the model.     

Bremsstrahlung in nucleon-nucleon collisions

The theory of bremsstrahlung in nucleon-nucleon collisions at non-relativistic energies is reviewed, with special emphasis on the possibility of drawing conclusions concerning the nucleon-nucleon interaction. The basic concepts are introduced in section 2, and illustrated in section 3 for the case of a separable interaction. Soft-photon theorems are discussed in section 4. Section 5 contains some brief comments on the comparison between theory and experiment. The theory needs a number of correction terms, which are discussed in section 6. A generalized Ward identity for bremsstrahlung, which relates the divergence of the contribution from internal lines to off-shell scattering amplitudes is also given.     

Photon production in nucleon-nucleon collisions

We calculate the differential cross section for nucleonnucleon bremsstrahlung in covariant way based on a realistic meson-exchange approximation for the NN-scattering amplitude. The results are discussed in comparison to semiclassical approximations and with respect to the role of internal radiation diagrams. The influence of the anomalous magnetic moment on the proton-neutron bremsstrahlung is found to contribute up to 50% for specific kinematical conditions. Recent measurements on the elementary differential cross sectionpnpn are found to be quite accurately reproduced. Furthermore, for use in proton-nucleus and nucleus-nucleus collisions, we present a parametrization of thepn cross section within a broad kinematical range.Work supported by BMFT, GSI Darmstadt and a NATO science grant     

Meson production in nucleon-nucleon collisions

I review some recent works on meson production in nucleon-nucleon collisions. In particular, I report on an investigation of the reaction NN → NNπ near threshold where the production amplitude has been evaluated within chiral perturbation theory up to next-to-leading order, using a counting scheme that takes into account the large scale introduced by the initial momentum. With regard to other meson-production reactions I focus on a phenomenological analysis of the Λ/Σ⁰ production ratio in pp collisions.     

Two-pion exchange nucleon-nucleon potential model independent features

A chiral pion-nucleon amplitude supplemented by the HJS subthreshold coefficients is used to calculate the the long range part of the two-pion exchange nucleon-nucleon potential. In our expressions the HJS coefficients factor out, allowing a clear identification of the origin of the various contributions. A discussion of the configuration space behaviour of the loop integrals that determine the potential is presented, with emphasis on cancellations associated with chiral symmetry. The profile function for the scalar-isoscalar component of the potential is produced and shown to disagree with those of several semi-phenomenological potentials.     

A model for multiplicity distributions in high energy collisions

A phenomenological model is presented which regards the system after collision as a single entity that emits hadrons directly. The evolution of this entity gives a new two parameter distribution which fits the high energypp, \(\bar pp\) ,e ⁺ e ^?, π⁺ p andK ⁺ p data reasonably well. The entity emits hadrons along the rapidity axis and exhibits intermittency behaviour under certain conditions.     

Very high energy nucleus-nucleus collisions and multi-chain model

Inclusive and semi-inclusive production of Λ and \(\bar \Lambda\) inK ⁺ p interactions is studied at an incident momentum of 70 GeV/c. Cross sections and single particle distributions are presented and compared with data at lower energies. Scaling is observed between 32 and 70 GeV/c in the Feynmanx variable in the target and the beam fragmentation regions for Λ and \(\bar \Lambda\) inclusive production respectively. An increase of Λ ( \(\bar \Lambda\) ) production is observed in the beam (target) fragmentation regions, whereas the data at 70 and 32 GeV/c are reasonably close in the central region. The dependence of the Λ( \(\bar \Lambda\) ) polarization as a function ofx is measured and found to be in general agreement with the results at 32 GeV/c. The (Λ \(\bar \Lambda\) ) pair production cross section increases significantly from 32 to 70 GeV/c. The Λ and \(\bar \Lambda\) production associated with an identified proton is also studied.     

A model for multiparticle production in high energy hadronic collisions

A model for multiparticle production process in high-energy hadronic collisions is proposed. In the centre of mass (CM) system of colliding particles the target and the projectile are assumed to pass through each other sharing energies allowed by kinematical constraints. Thus in app collision the energy associated with each is √S/2 (S being the square of the CM energy) which is taken to be the real variable that governs the number of particles produced. In the case of hadronnucleus collisions the projectile and the target ofv nucleons lying in a (Lorentz contracted) tube pass through each other sharing energies ⋍ √S _A2, whereS _A ⋍vS. Before the final state particles emerge from these systems, the constituents of the target, i.e.,v nucleons share equally (= √S _A2v) the total energy associated with the target and become the centres from which final state particles stem out. Several results have been discussed.     

The FRITIOF model for very high energy hadronic collisions

We implement the high-P _T dynamics, namely parton scattering of the Rutherford type, into the framework of the FRITIOF model. Such high-P _T effects are increasingly important in hadronic collisions at higher energies and it is crucial to include them for a model intended to describe the collision and particle production processes. In our treatment the Rutherford parton scattering (RPS) is intimately related to the gluon bremsstrahlung radiation. By investigating their interrelation we arrive at a FRITIOF implementation of RPS which is infrared stable. The results of the model are in excellent agreement with experimental data up to the highest energies. The model predicts a restoration of KNO scaling as a good approximation in the TeV energy regime.     

Threshold open charm production in nucleon-nucleon collisions

The associative charm particles production in nucleon-nucleon collisions N + N↦Λ_c(Σ_c) + ˉD + N, is described in a general way and the spin and isospin structure of the corresponding matrix elements are derived. Using an analogy with strange-particle (ΛK) production, the D-meson exchange model is considered in detail. Estimations of the energy behavior of the threshold cross-sections show a large dependence on the form of the phenomenological hadron form factors and indicate that, at threshold, the cross-section is three orders of magnitude smaller than for strange-particle production. Received: 18 October 2002 / Accepted: 5 December 2002 / Published online: 18 March 2003 RID="a" ID="a"Permanent address: National Science Center KFTI, 310108 Kharkov, Ukraine. RID="b" ID="b"e-mail: etomasi@cea.fr Communicated by V.V. Anisovich     

Scalar-meson production in nucleon-nucleon collisions near threshold

We establish the model-independent spin structure of the matrix elements for the near-threshold scalar-meson production in pp and np collisions, when the final particles are emitted in S-state. Polarization phenomena are derived in a general form. The properties of the t-channel dynamics, which is based on different meson exchanges, are studied in terms of the s-channel parametrization of the matrix element. The predictions of a model, based on exchanges are also presented.Received: 1 April 2003, Published online: 11 November 2003PACS: 13.75.Cs Nucleon-nucleon interactions (including antinucleons, deuterons, etc.) - 21.10.Hw Spin, parity, and isobaric spin - 13.88. + e Polarization in interactions and scatteringM.P. Rekalo: Permanent address: NSC-Kharkov Institute of Physics and Technology, 310108 Kharkov, Ukraine.     

Factorization in high energy hadron collisions

The concept of factorization is discussed for elastic diffraction scattering and diffraction dissociation of hadrons at high energy. In addition to the usual definition in terms of the t-channel, a natural definition of factorization in the s-channel is proposed and compared with the former. It is shown that s-channel factorization of all diffractive processes is consistent with the assumption that elastic scattering is identical to the shadow of the diffraction dissociation processes.     

高能重离子碰撞中的参与者数和核子-核子碰撞数

采用核-核碰撞的Glauber模型, 给出了高能重离子碰撞中的参与者数和核子-核子碰撞数随碰撞参数的分布方程, 并用其讨论了\{s_NN\}^1/2=200GeV的Au+Au碰撞中的参与者数与核子-核子碰撞数随对心度的变化关系, 所得结果与PHENIX合作组所给出的实验结果符合得很好. 关键词： Glauber 模型 参与者数 核子-核子碰撞数     

Thermalization in high energy nuclear collisions

complete events of the symmetric collisions Ca + Ca at E/A = 400 MeV and 1050 MeV and Nb + Nb at E/A = 400 MeV and 650 MeV have been measured with the Plastic Ball/Wall 4π spectrometer. The degree of isotropy expressed by the ratio of the mean transverse to the mean longitudinal momentum in each event is determined as a function of the charged particle multiplicity. Also discussed are proton energy distributions at θ_cm = 90° and their multiplicity dependences.     

Regge-eikonal model for high energy elastic diffractive nucleon-nucleon scattering with a minimum number of reggeons

A phenomenological Regge-eikonal model with nonlinear monotonic parameterizations for Regge trajectories in which their asymptotic behavior in the perturbative region is taken into account explicitly is proposed. It is shown with the example of elastic proton-(anti)proton scattering that in the kinematic region \(\sqrt s \) > 23 GeV, 0.005 GeV² < ?t < 3 GeV², the diffraction pattern is mainly determined by only three Regge trajectories.     

Analysis of cosmic ray data on nucleon-nucleus collisions and its implication on high energy behaviour of nucleon-nucleon total cross section

From existing cosmic ray measurements of theinelastic collision cross sections of nucleons on nuclei of carbon, iron and lead in the range of energies 10² to 10⁴ GeV as well as the measurements of cross sections on air nuclei in the extensive air shower (EAS) regions (10⁵ to 10⁸ GeV), we conclude that the Glauber multiple scattering theory is adequate to account for the data. Recent suggestion of Maor and Nussinov to parametrize the nucleon-nucleon total cross section with a component growing proportional to ln² E (E is the incident energy) is at variance with the EAS data. However the data are consistent with a nucleon-nucleon total cross section rising no faster than lnE in these energy regions.     

Systems of oscillators with statistical energy exchange in collisions

Classical transition probabilities are derived for the exchange of energy between sets of weakly coupled harmonic oscillators, subject to the assumption that energy is ‘statistically redistributed’ in all collisions. In the case of single oscillators the result is particularly simple and an explicit solution of the relaxation equation for such a system is derived. A ‘mean first passage time’ for the dissociation of truncated harmonic oscillators is also obtained using Widom's theory and the limiting case of equilibrium reaction is discussed.

The same approach is sketched briefly for the case of quantized systems in which statistical redistribution of energy is allowed.

Within the general scope of the model, these transition probabilities represent the most efficient conceivable coupling between system and heat bath.     

Two-pion exchange in the nucleon-nucleon potential

The two-pion-exchange potential is calculated using experimental ππ, πN and eN information and compared with the Hamada-Johnston and deTourreil-Sprung phenomenological potentials. The calculated potential is found to be in very satisfactory agreement with the phenomenological values at radii greater than 1.2 to 1.5 fm except in the isospin-zero spin-orbit case. The potential is somewhat sensitive to the low-energy I=J=0 ππ interaction, which is still experimentally uncertain.