Argon L x-ray spectra from collisions of argon ions with various solid state targets

Spectral measurements have been made of Ar-L-shell X-rays produced by Ar ions incident on various solid state targets. Different spectra have been observed for targets with Z < 18 and Z > 18 respectively. The data are discussed within the framework of the electron promotion model of Barat and Lichten.     

Peripheral collisions of relativistic heavy ions

The physics of peripheral collisions with relativistic heavy ions (PCRHI) is reviewed. One- and two-photon processes are discussed.     

Trends of light particle spectra observed in nucleus-nucleus collisions

The emission of energetic light particles (p,d,t) has been studied for ¹⁶O induced reactions on Al, Zr and Au targets at the incident energies of 140, 215 and 310 MeV. The light-particle energy spectra have been analyzed in terms of a moving thermal source. The apparent temperatures exhibit a systematic variation as a function of the incident energy per nucleon above the Coulomb barrier. The observed trend can be extrapolated in a smooth fashion to temperatures obtained in relativistic heavy-ion collisions.     

Multifragmentation in peripheral collisions of relativistic heavy ions

The breakup of heavy ions in peripheral collisions at relativistic energies offers a rich field of nuclear studies such as the investigation of nuclear structure, the production of energetic beams of exotic nuclei and studies of hot nuclear matter. Examples of recent experimental results obtained at GSI Darmstadt with the heavy ion synchrotron SIS will be discussed with emphasis on the nuclear breakup in the domain from distant collisions without nuclear contact by Coulomb excitation, to peripheral collisions with increasing overlap between projectile and target. The production of relativistic beams of exotic nuclei by fragmentation opens up a new area of nuclear structure research.Invited lecture given at the International School-Workshop Relativistic Heavy-Ion Physics, Prague (Czech Republic), 19–23 September 1994.     

The critical distance in collisions of heavy ions

There is a large discrepancy in published values of the critical distance in heavy-ion collisions. We have recalculated the critical distance by a more accurate method for symmetric collisions of point nuclei as a function of Z. The reasons for the discrepancy are discussed.     

Emission of direct particles in heavy ions collisions

This paper presents a theoretical model for the emission of fast light particles derived from the PEP (Promptly Emitted Particles) model. This model is extended to the emission of fast alpha particles. With some restrictions, analytical formulae are derived for the production rate and the mean angular momentum associated with fast particles. Most of the qualitative features predicted by the analytical formulae are confirmed by the numerical results obtained from a more realistic calculation where the trajectories of the particles are followed during the whole collision. It is argued that PEP alpha particles emitted preferentially in low angular momentum collisions, could represent the major part of the fast alpha particles observed in incomplete fusion reactions.     

Molecular dynamics for collisions of heavy ions

Ying-Xun Zhang, Ning Wang, and their collaborators systematically reviewed the molecular dynamics and its application to heavy ion collisions at low and intermediate energies [6].     

Charge exchange in collisions between heavy low-charged ions

The probabilities and the effective cross sections of collision-induced one-electron charge exchange between singly charged and four-charged heavy Xe, Cs, Ba, Pb, Bi, and U ions at energies E>0.1 keV/u are calculated by a method of multichannel normalization in the impact parameter representation. The cross sections are rather large with a maximum σ_m≈10⁻¹⁵ cm² at relative energies E _m ≈10–30 keV/u. For collision energies E<10 keV/u, the cross sections sharply decrease with growing resonance defect of the reaction. At high energies E>1 MeV/u, the charge exchange proceeds largely by the capture of inner shell electrons of the ionic targets. The charge exchange cross sections calculated for low-charged Xe, Cs, Ba, Pb, Bi, and U ions are compared with available theoretical and experimental data.     

Average polarization in deep inelastic collisions of heavy ions

The polarization averaged over many quantal channels is analyzed. The analytical expressions for probability distribution function and average polarization are derived in cases of pure statistical reactions as well as the planar ones.     

Strange particle production in relativistic collisions of heavy ions

This review examines data on strange particle production in Pb + Pb collisions obtained in heavy ion experiments at CERN SPS. The yields of K, Λ, Ξ and Ω are considered, as well as their rapidity and transverse mass distributions, depending on the centrality of Pb + Pb collisions at SPS energies. Experimental results are compared with predictions of the statistical nuclear fireball and microscopic parton -string models. We discuss in detail the experimentally observed effect of strangeness enhancement in nucleus-nucleus collisions as compared to nucleon-nuclear interactions and its interpretation within the framework of various theoretical models. Also, we analyze the behavior of hyperon yields and nuclear modification factors in passing from SPS to RHIC energies.     

Ionization of heavy ions in relativistic collisions with neutral atoms

The problem of ionization of ions in ion-ion and ion-neutral relativistic collisions is considered. Formulas for ionization cross sections are derived in the Born approximation in terms of the momentum transfer without allowance for magnetic interactions. Using these formulas implemented in the LOSS-R code, the ionization cross sections are calculated for the K shells of neutral atoms colliding with protons and also for 1s and 2p electrons of multiply charged heavy ions (nuclear charge Z = 80−90) colliding with bare nuclei and neutral atoms. The calculation results are compared with experimental data and calculations of other authors.     

Prediction of the azimuth angle dependence of the quasimolecular anisotropy in heavy ion collisions

Within the quasimolecular (MO) kinematic dipole model we predict a strong dependence of the anistropy of the MO radiation on the orientation of the heavy ion scattering plane relative to the photon detection plame.     

Inclusive meson production in peripheral collisions of ultrarelativistic heavy ions

There exist several proposals to use Weizsäcker-Williams photons generated by ultrarelativistic heavy ions to produce exotic particles in γγ fusion reactions. To estimate the background conditions for such reactions we analyze various mechanisms of meson production in very peripheral collisions of ultrarelativistic heavy ions at RHIC and LHC energies. Besides the γγ fusion they include also electromagnetic γA interactions and strong nucleon-nucleon interactions in grazing AA collisions. All these processes are characterised by low multiplicities of produced particles. The γA an d AA events are simulated by corresponding Monte Carlo codes, RELDIS and FRITIOF. In each of these processes a certain fraction of pions is produced close to the mid-rapidity regionthat gives a background for the γγ events. The possibility of selecting the mesons produced in the γγ fusion events via different p _t cut procedures is demonstrated.     

Helicity representation for deep inelastic collisions of heavy ions

Quantum-mechanical cross-section for the inelastic collisions characterized by large values of the angular momenta is analysed. For the case of a planar mechanism of the reaction the approximation of the small helicity is drawn.     

1sσ ionization in high-energy collisions of very heavy ions

The production of completely empty K-shells is predicted for Pb + U collisions with E_lab ? 200 MeV/u. This is a necessary condition for the formation of naked heavy nuclei. Within the quasimolecular basis the electron excitation has been calculated including the radial and rotational coupling as well as the magnetic interaction induced by the heavy-ion current. The spin polarization of the created K-vacancies was found to be typically of the order of 10–20%.     

The coulomb glory effect in collisions of antiprotons with heavy ions

The Coulomb glory effect in the back scattering of antiprotons with energies of from 100 eV to 3 keV from a bare nucleus of uranium and from uranium ions with closed shells is considered in terms of nonrelativistic and relativistic quantum theory. The appearance of Coulomb glory in collisions with multiply charged ions is caused by nucleus charge screening by filled electron shells. In scattering from a bare nucleus, the effect appears because of the screening properties of the vacuum polarization potential.     

Ionization loss of relativistic structural heavy ions in collisions with atoms

A nonperturbative theory of energy loss in collisions between structural, highly charged heavy ions moving at relativistic velocities and atoms is developed. A simple formula for effective deceleration is derived. By structural ions are meant ions containing partially filled electron shells. It is such ions characterized, as a rule, by a significant charge (for example, partially “stripped” uranium ions) that are used in numerous experiments involving the use of modern heavy-ion accelerators.     

Spatial anisotropy: a method to study anisotropic flow in heavy ion collisions

We introduce a method to study anisotropic flow parameter v_n as a collective probe to Quark Gluon Plasma in relativistic heavy ion collisions. The emphasis is put on the use of the Fourier expansion of initial spatial azimuthal distributions of participant nucleons in the overlapped region. The coefficients ε_n of Fourier expansion are called the spatial anisotropy parameter for the n-th harmonic. We propose that collective dynamics can be studied by v_n/ε_n. In this paper, we will discuss in particular the second (n=2) and the fourth (n=4) harmonics.