Event-shape-engineering study of charge separation in heavy-ion collisions

Recent measurements of charge-dependent azimuthal correlations in high-energy heavy-ion collisions have indicated charge-separation signals perpendicular to the reaction plane, and have been related to the chiral magnetic effect(CME). However, the correlation signal is contaminated with the background caused by the collective motion(flow) of the collision system, and an effective approach is needed to remove the flow background from the correlation. We present a method study with simplified Monte Carlo simulations and a multi-phase transport model,and develop a scheme to reveal the true CME signal via event-shape engineering with the flow vector of the particles of interest.     

Manifestation of exchange effects in heavy-ion interactions

Three different approaches to taking into account exchange effects in heavy-ion collisions are studied. Within the first of them, the lowest eigenstates of the Hamiltonian are treated as forbidden states. In the second approach, the eigenstates of the normalization kernel of the resonating-group model that correspond to zero eigenvalues are treated as forbidden states. The third approach takes additionally into account semiforbidden states. The ¹⁶O + ¹⁶O system is considered. A hybrid approach that combines the methods of discrete and continuous mathematics is developed for calculating the widths of narrow resonance states. The resonance width calculated within the approach that takes into account semiforbidden states proves to be sharply different from the widths obtained within traditional approaches.     

Time-dependent Hartree-fock description of charge equilibration in heavy-ion collisions

We have performed a time-dependent Hartree-Fock calculation for the ${}^{16}\text{O}\text{+}{}^{40}\text{Ca and}{}^{16}\text{O}\text{+}{}^{48}\text{Ca}$ systems to study charge equilibration, which is found to be related to the longitudinal component of the giant dipole resonance of the composite system. The quantities which can be deduced from the calculation are in agreement with those used in phenomenological calculations.     

Space charge effect and mirror charge effect in photoemission spectroscopy

We report the observation and systematic investigation of the space charge effect and mirror charge effect in photoemission spectroscopy. When pulsed light is incident on a sample, the photo-emitted electrons experience energy redistribution after escaping from the surface because of the Coulomb interaction between them (space charge effect) and between photo-emitted electrons and the distribution of mirror charges in the sample (mirror charge effect). These combined Coulomb interaction effects give rise to an energy shift and a broadening which can be on the order of 10 meV for a typical third-generation synchrotron light source. This value is comparable to many fundamental physical parameters actively studied by photoemission spectroscopy and should be taken seriously in interpreting photoemission data and in designing next generation experiments.     

Pre-equilibrium dipole strength in charge asymmetric peripheral heavy-ion reactions

We report on the results obtained from the study of the ³²S + ⁶⁴Ni and ³²S + ⁵⁸Ni peripheral reactions at incident energies E _lab = 288 MeV and E _lab = 320 MeV, respectively. High-energy γ-rays were detected in an array of 8 seven-pack BaF₂ clusters. Coincidence with complex fragments detected in 12 three-stage telescopes ensured the selection of peripheral reaction events. All of the relevant reaction parameters were kept constant with the exception of the different initial dipole moment caused by the different entrance channel charge asymmetry. While for quasi-elastic events no N/Z effect was observed in the differential γ-ray multiplicities of the two reactions, for deep-inelastic events a larger dipole γ-ray emission occurs during the more N/Z asymmetric reaction. A theoretical interpretation based on a collective Bremsstrahlung analysis of the reaction dynamics is presented. Received: 26 September 2002 / Accepted: 13 November 2002 / Published online: 6 March 2003 RID="a" ID="a"e-mail: pierroutsakou@na.infn.it RID="b" ID="b"Present address: INFN, Laboratori Nazionali di Legnaro, Padova, Italy. Communicated by C. Signorini     

On the time scale of charge equilibration in heavy-ion reactions

The typical time for charge equilibration in heavy-ion reactions is estimated in a microscopic and a hydrodynamical model analoguous to the Goldhaber-Teller model for the giant dipole resonance and is found to be of the order of 10^-22 s if friction is disregarded. It is discussed to which extent experimentally determined equilibration times allow for dissipative forces in the equilibration degree of freedom.     

Pion-nucleus charge exchange reactions

This is a report on the single and double charge exchange reactions on nuclie. The emphasis is on recent experimental results and calculations. We limit ourselves to pion energies below 300 MeV. The experimental results and complexity. We present the current level of understanding of the various aspects of the charge exchange process.     

Development of a laser cleaning method for the first mirror surface of the charge exchange recombination spectroscopy diagnostics on ITER

Physics of Atomic Nuclei - A set of optical diagnostics is expected for measuring the plasma characteristics in ITER. Optical elements located inside discharge chambers are exposed to an intense...     

Muon charge exchange and muonium spin exchange in gases

The spin dynamics of the positive muon undergoing cyclic charge exchange (μ⁺⇌Mu) while it is slowing down is compared with that in the case of repeated muonium spin exchange after thermalization. The expectation value of the spin polarization at timet aftern spin exchange collisions (att ₁,t ₂, ...,t _n ) are calculated explicitly from time dependent wave functions, and the quantity is averaged over the statistical distribution of the times of collisions and over all possible numbers of collisions betweent=0 and the observation timet. This result is complementary and equivalent to the conventional density matrix formalism, but offers an insight into the roles of spin flip and spin non-flip processes. The neutral fraction during slowing down is also discussed.     

First quantization of mass and charge

The proper time is introduced as a parameter into the wave functions of relativistic quantum theory by first quantization of the mass. The classical limit is shown to be given by a recently developed canonical formulation of classical relativistic mechanics. The adjoint spinor is redefined with the help of a sign operator to remove a discrepancy between the classical and quantum actions in the behavior under time inversion. This results in positive energy densities for the Dirac theory. The inclusion of this sign operator into the definition of the probability current then removes negative probabilities from the theory. A five-dimensional formulation with first quantized charge is given.     

Pion-nucleus inelastic scattering and charge exchange

Using a separable fixed scatterer pion-nucleon interaction and the distorted wave impulse approximation we have made predictions for medium energy pion inelastic scattering from ¹⁶O and (π^?, π⁰) charge exchange from ⁴⁸Ca. An optical potential based on the pion-nucleon interaction adopted in this work has been shown previously to provide good fits to pion-nucleus elastic scattering. After a discussion of the basic formulae, we present results of calculations for pion inelastic scattering from ¹⁶O for initial pion lab kinetic energies of 70 and 180 MeV. Because of the strong energy dependence of the pion-nucleon interaction there are qualitative differences between the predictions for the nuclear response in the momentum transfer, energy loss plane for T_π^lab = 70 and 180 MeV. At these energies, states not prominently excited by other probes are predicted to be observable. In particular, J^π = 3^? and 4^?, T = 0 states appear prominently in the excitation spectrum region at large momentum transfer. A comparison of π^? and π⁺ scattering showing the effects of the Coulomb interaction is presented. The predictions for pion single-charge exchange on ⁴⁸Ca indicate that this interaction would be useful for studying the location of the T_> states arising from the splitting of the giant dipole resonance in T ≠ 0 nuclei.     

Theory of charge exchange of vector bosons

An investigation is made of the well-known Klein paradox, which is formulated in the Sakata — Taketani representation. It is shown that when a vecton passes from a region with V(x)=0 into a region with V(x)2mc² it can go over into an antiparticle state. It is concluded that in this problem the spin does not affect the process.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 84–87, October, 1974.     

Theory of charge exchange scattering from surfaces

We present a simple model calculation of the charge exchange probability for ions scattering from solid surfaces, including interactions with both broad band delocalized electrons and with localized core electrons within an Anderson type Hamiltonian with time dependent parameters. The results exhibit some of the major observed experimental features, including characteristic oscillations as a function of incident velocity (from quasi-resonant electron interchange with the core levels) and overall exponential decay $\text{～exp}\text{(?A}\text{v)}$, with v the incident ion velocity, from interactions with the broad band electrons.     

Dissipation,mass exchange and the microscopic time scale of heavy-ion collisions

The time scale provided by the nucleon exchange mechanism in heavy-ion reactions is employed to study kinetic energy damping. The experimental kinetic energy lost per nucleon exchanged in Kr- and Xe-induced reactions is observed to decrease linearly with the total kinetic energy loss. These results, which are consistent with energy dissipation and nucleon exchange occuring on a similar time scale, are compared with the predictions of a one-body dissipation mechanism and a diffusion model.     

Contribution of the σ meson exchange to pionic double charge exchange reaction

The contribution of the σ meson exchange to the pionic double charge exchange (DCX) reaction is investigated. A concrete calculation on the forward excitation function of the low energy DCX reaction ¹⁴C(π⁺, π⁻)¹⁴O has been performed. It shows that the contribution of the σ meson exchange can reproduce well the resonance like excitation function of low energy DCX reaction. Received: 5 August 1998