On the coherent inelastic processes in collisions of elementary particles with nuclei at ultrarelativistic energies

The coherent inelastic processes of the type a → b, which may take place in the interaction of hadrons and γ quanta with nuclei at very high energies (the nucleus remains the same), are theoretically investigated. Analytical formulas for the effective cross-section σ_coh(a→b) are obtained.     

On the semiclassical theory of inelastic,atom-molecular collisions

A general semiclassical theory of energy exchange in the three-dimensional collisions between an atom and a diatomic molecule is formulated. The interaction in the time-dependent Schrödinger equation, giving rise to inelastic transitions, is defined in terms of the exact classical trajectories of the colliding particles. These trajectories were specified by the condition, that the molecule was not vibrating before the collision. It is shown, that such approach gives the results coinciding in a number of cases with those obtained with the help of the exact quantum-mechanical methods. The results obtained for the particular case of the impulsive atom-molecular collisions were used for the interpretation of new phenomena observed in the experiments on the dissociation of some molecular ions in the collisions with the neutral helium atoms.     

Multiscaling in inelastic collisions

We study relaxation properties of two-body collisions on the mean-field level. We show that this process exhibits multiscaling asymptotic behavior as the underlying distribution is characterized by an infinite set of nontrivial exponents. These nonequilibrium relaxation characteristics are found to be closely related to the steady state properties of the system.     

On distributions of antibaryons in\bar p-Nucleus inelastic collisions

In the framework of the dual parton model we calculate the spectra of secondary antibaryons in \(\bar p\) -nucleus non-annihilation inelastic interactions. We find that the number of antibaryons in the backward hemisphere in the \(\bar p\) -nucleon centre-of-mass frame can grow with the atomic number of the nucleus.     

On inelastic screening inK S regeneration on nuclei

We discuss the inelastic screening corrections to the kaon-nucleon total cross-sections andK _S regeneration on nuclei in the framework of the parton model of diffraction scattering.     

Coherent collisions between Bose-Einstein condensates

We study the nondegenerate parametric amplifier for matter waves, implemented by colliding two Bose-Einstein condensates. The coherence of the amplified waves is shown by observing high contrast interference with a reference wave and by reversing the amplification process. Since our experiments also place limits on all known sources of decoherence, we infer that relative number squeezing is most likely present between the amplified modes. Finally, we suggest that reversal of the amplification process may be used to detect relative number squeezing without requiring subshot-noise detection.     

Ultracold inelastic collisions in two dimensions

We show that cross sections for inelastic collisions of ultracold atoms or molecules confined by a harmonic potential have the same energy dependence as in pure 2D geometry. This indicates that chemical reactions and inelastic collisions may be suppressed in an ultracold gas under strong confinement in one dimension. We present a numerical proof of the threshold collision laws in 2D. Our results indicate that inelastic collisions in weak electromagnetic fields may be controlled by varying the orientation of the external field axis with respect to the plane of confinement.     

On inelastic reactive collisions in kinetic theory of chemically reacting gas mixtures

A kinetic theory for a simple reversible reaction-characterized by a binary mixture of ideal gases whose constituents denoted by A and B undergo a reaction of the type A+A?B+B-is developed by considering the reactive collisions as inelastic ones. The geometry of the collision is taken into account in the line-of-centers differential cross section by allowing that a chemical reaction may occur only when the energy of the relative velocity in the direction of the line which joins the centers of the molecules at collision is larger than the activation energy. It is shown that the restitution coefficients: (i) depend explicitly on the reaction heat and on the relative translational energy in the direction of the line which joins the centers of the molecules during an inelastic collision; (ii) vanish when the reaction heat is zero; (iii) are larger or smaller than one depending on the direction of the reaction and on the sign of the reaction heat. First approximations to the distribution functions are determined from the system of Boltzmann equations for the last stage of a chemical reaction. It is shown that the deviations from the Maxwellian distribution functions and the production terms of the particle number densities: (i) vanish when the reaction heat is zero provided that the affinity is close to zero and (ii) are negative or positive depending on the sign of the reaction heat and on the direction of the reaction.     

Spin effects in inelastic electron-atom collisions

Recent progress of experimental investigations that show explicitly spin-dependent effects is reported for inelastic electron-atom scattering. In particular the combined effect of exchange scattering and target coupling is discussed in more detail. The experimental investigation of this ‘target-coupling effect’ is a powerful method to study the influence of exchange scattering directly. The experiments that are reviewed are basically target and electron spin-polarization measurements and the determination of the angular momentum state of the atom after scattering.     

On the origin of the flow angle in high-energy collisions of heavy nuclei

We expose a “test” participant nucleon to the moving projectile and target spectator nuclear mean fields. A net attraction of the participant is found which results in a sizeable flow angle in collisions of heavy nuclei at an incident energy of 400 MeV/nucleon.     

Angular-momentum coherence in heavy-ion deep inelastic collisions

It is shown that cross sections describing deep inelastic collisions between complex nuclei can neither be desribed as a coherent nor as an incoherent superposition of partial-wave amplitudes. The number of interfering partial waves increases with the masses of the interacting nuclei and decreases with the interaction time.     

The third particle in deep inelastic collisions

Angular correlations between charged reaction products have been measured for the reaction¹⁴N+²⁷A1 at 70 and 100 MeV. Light particle evaporation from the heavy recoil is shown to be the dominant process. In addition, however fast alphas are observed for all reaction channels. From the three-body kinematics we conclude that these alphas are emitted from the contact zone between the two heavy ions. A comparison of the results forE _Lab=70 and 100 MeV excludes an explanation of this process by the recently suggested “Piston” or “hot-spot” models.     

Bose-Einstein correlations of neutral gauge bosons in pp collisions

The theory for Bose-Einstein correlations in case of neutral gauge bosons in pp collisions at high energies is presented. Based on quantum field theory at finite temperature, the two-particle Bose-Einstein correlations of neutral gauge bosons are carried out for the first time. As a result, the important parameters of the correlation functions can be obtained for the Z ⁰ Z ⁰ pairs. The article is published in the original.     

Relativistic hadronic cascade analysis of two-pion Bose-Einstein correlation for Si + Au collisions at AGS energy

Using a simple kinetic model we study whether a pion condensate can be formed during the hadronization of the quark-gluon plasma in ultra-relativistic heavy-ion collisions. Unless the effective mass of the hadronizing pions is close to zero, no onset of the Bose-Einstein condensation is observed. The constraints on the condensation process coming from the requirement of the entropy increase are discussed in detail.     

On a microscopic mechanism of collisions between extremely light nuclei

The method previously proposed by one of the present authors for studying three-body problems is generalized with the aim of exploring more complicated nuclear processes. The idea underlying the method consists in preserving the unitarity property for the scattering amplitude determined approximately. A specific analysis is performed for elastic collisions of ³He nuclei and for quasielastic deuteron-triton collisions. The theoretical results obtained by our method are compared with experimental data, and the agreement is found to be quite satisfactory.