Nucleus-nucleus Interactions Research Articles

Low-energyHe6scattering in a microscopic model

A microscopic version of the Continuum Discretized Coupled Channel (CDCC) method is used to investigate $^{6}$He scattering on $^{27}$Al, $^{58}$Ni, $^{120}$Sn, and $^{208}$Pb at energies around the Coulomb barrier. The $^{6}$He nucleus is described by an antisymmetric 6-nucleon wave function, defined in the Resonating Group Method. The $^{6}$He continuum is simulated by square-integrable positive-energy states. The model is based only on well known nucleon-target potentials, and is therefore does not depend on any adjustable parameter. I show that experimental elastic cross sections are fairly well reproduced. The calculation suggests that breakup effects increase for high target masses. For a light system such as $^{6}$He+$^{27}$Al, breakup effects are small, and a single-channel approximation provides fair results. This property is explained by a very simple model, based on the sharp-cut-off approximation for the scattering matrix. I also investigate the $^{6}$He-target optical potentials, which confirm that breakup channels are more and more important when the mass increases. At large distances, polarization effects increase the Coulomb barrier, and provide a long-tail absorption component in the imaginary part of the nucleus-nucleus interaction.

Energy dependence of fluctuations in p+p and Be+Be collisions from NA61/SHINE

The main aims of the NA61/SHINE experiment are to discover the critical point of strongly interacting matter and to study properties of the onset of deconfinement. For these goals a two dimensional scan of the phase diagram (T-µb) is being performed at the SPS with measurements of hadron production in proton-proton, proton-nucleus and nucleus-nucleus interactions as a function of collision energy and system size. It is expected that fluctuations of various dynamical quantities will increase close to the critical point. In this contribution recent results of measurements of fluctuations in p+p and Be+Be collisions at SPS energies are presented as well as comparisons with model predictions and corresponding data of other experiments are discussed.

Geometry and Space-Time Extent of Pion Emission Region at FCC Energies

The energy dependence is investigated for a wide set of space-time characteristics derived from Bose–Einstein correlations of secondary pion pairs produced in proton-proton and nucleus-nucleus interactions. Analytic functions suggested for smooth approximations of the energy dependence of emission region parameters demonstrate reasonable agreement with all available experimental results for proton-proton collisions while the approximations correspond to most of experimental data for nucleus-nucleus collisions at energies above 5 GeV. Estimations for a wide set of space-time quantities are obtained for energies for the Future Circular Collider (FCC) project based on the smooth approximations. The space particle densities at freeze-out are derived also from estimations for the volume of the emission region and for total multiplicity at FCC energies. Estimations for charged particle density and its critical value allow the possibility of lasing behavior for secondary pions in nucleus-nucleus collisions at FCC energy. The mathematical formalism is presented for study of the peak shape of correlation function for general case of central-symmetrical Lévy–Feldheim distribution.

Study on initial geometry fluctuations via correlation of finite distributions of secondary particles in nucleus-nucleus interactions

The study of the peculiarities of the distribution of secondary particles depending on the degree of centrality and the degree of asymmetry of the interacting nuclei, is performed. The number of multicharged fragments of the projectile nucleus (Nf) in interactions of sharply asymmetric nuclei depends on the centrality degree of interaction. In the majority of peripheral interactions Nf is equal 1. In the most of the central interactions there are Nf > 1 or Nf=0. At that, the events with Nf =1 are separated clearly in the distribution of the total charge of the fragments of a projectile nucleus (Q) depending on the nature of the correlation of the number of fragments of the target nucleus (Nh) and the multiplicity of secondary particles from interaction area (ns). The peak in the field of the maximum values of Q characterizes peripheral events with various degree of the periphery on a growing branch of average Nh-ns curve. And the peak in the field of small Q characterizes the central events with various degree of centrality on the decreasing branch of average Nh-ns curve.

Recent results from NA61/SHINE

The NA61/SHINE experiment aims to discover the critical point of strongly interacting matter and study the properties of the onset of deconfinement. For these goals a scan of the two dimensional phase diagram (T-$\mu_B$) is being performed at the SPS by measurements of hadron production in proton-proton, proton-nucleus and nucleus-nucleus interactions as a function of collision energy and system size. In this contribution intriguing results on the energy dependence of hadron spectra and yields in inelastic p+p and centrality selected Be+Be collisions will be presented. In particular, the energy dependence of the signals of deconfinement, the 'horn', 'step' and 'kink', in p+p interactions will be presented and compared with the corresponding results from central Pb+Pb collisions from NA49.

Universality of particle production and energy balance in hadronic and nuclear collisions

The multihadron production in nucleus-nucleus and (anti)proton-proton col- lisions is studied by exploring the collision-energy and centrality dependencies of the mean multiplicity in the existing data. The study is performed in the framework of the re- cently proposed effective-energy approach which combines the constituent quark picture and Landau hydrodynamics counting for the centrality-defined effective energy of partic- ipants. Within this approach, the multiplicity energy dependence and the pseudorapidity spectra from the most central nuclear collisions are well reproduced. The study of the multiplicity centrality dependence reveals a new scaling between the measured pseudora- pidity spectra and the calculations. Using this scaling, called the energy balanced limiting fragmentation scaling, the pseudorapidity spectra are well reproduced for all centralities. The scaling clarifies some differences in the multiplicity and midrapidity density central- ity dependence from RHIC and LHC. A similarity in the multiplicity energy dependence in the most central collisions and centrality data is shown. Predictions are drawn for the mean multiplicities to be measured in hadronic and heavy-ion collisions at the LHC. 1. In this report, we discuss our recent results on the universality of multiparticle production in nucleus-nucleus (AA) and hadronic interactions in view of a new scaling obtained (1). The study ex- ploites concept of effective energy (2) employed for the data interpreted in terms of the approach of the dissipating energy of quark participants (3, 4), or, for brevity, the participant dissipating energy (PDE) approach. This approach combines the constituent quark picture together with Landau relativistic hy- drodynamics and interrelates different types of collisions. The earlier observations (2) are made by studying the dependencies of the pseudorapidity density and transverse energy pseudorapidity den- sity at midrapidity on the collision center-of-mass (c.m.) energy in hadronic and the most central (head-on) AA collisions and on the number of nucleon participants, or centrality, in AA collisions in the entire available energy range of the existing data. The complementarity of the measurements in

Energy scan of correlations in p+p and Be+Be from NA61/SHINE

The existence of the critical point (CP) of strongly interacting matter is still an open problem. An extensive strong interactions program including a search of the CP and the study of the onset of deconfinement was started by the NA61/SHINE experiment at the CERN SPS. A two dimensional scan of the phase diagram is performed to search for the CP and to shed light on the phase transition region. This program includes studies of hadron production in proton- proton, proton-nucleus and nucleus-nucleus interactions measured in a wide range of colliding energy and system size. Correlations between various observables measured at midrapidity as well as in separated rapidity intervals are considered as additional and sensitive tools of this phase diagram scan. We present NA61/SHINE results of studies of energy dependence of two- particle correlations of pseudo-rapidity and azimuthal angle in p+p collisions at the SPS and the first results on correlations between multiplicity and mean transverse momentum in 7Be + 9Be collisions at 150A GeV/c obtained for separated pseudo-rapidity intervals (so called long-range correlations). Comparison with data calculations using the EPOS 1.99 model are also discussed.

27aSP-4 原子核の副虹の存在と動的核間相互作用

27aSP-4 原子核の副虹の存在と動的核間相互作用

The nucleus-nucleus scattering in transfer ionization of helium by He2+ impact

SynopsisWe have performed kinematically complete measurement on transfer ionization of He by 50 keV/u He2+ impact. The data were analyzed in terms of Dalitz spectrum. We evaluated the role of three particles interactions and found that the main momentum exchange occurs between the projectile and the recoil ion. This result indicate that the nucleus-nucleus high order interaction could not be overlooked in transfer ionization collision dynamics of atom by intermediate energy ion impact.

Anion emission from water molecules colliding with positive ions: Identification of binary and many-body processes

It is shown that negative ions are ejected from gas-phase water molecules when bombarded with positive ions at keV energies typical of solar-wind velocities. This finding is relevant for studies of planetary and cometary atmospheres, as well as for radiolysis and radiobiology. Emission of both H- and heavier (O- and OH-) anions, with a larger yield for H-, was observed in 6.6-keV 16O+ + H2O collisions. The ex-perimental setup allowed separate identification of anions formed in collisions with many-body dynamics from those created in hard, binary collisions. Most of the ani-ons are emitted with low kinetic energy due to many-body processes. Model calcu-lations show that both nucleus-nucleus interactions and electronic excitations con-tribute to the observed large anion emission yield.

Many-body perturbation theory approach to the electron-phonon interaction with density-functional theory as a starting point

The electron-phonon interaction plays a crucial role in many fields of physics and chemistry. Nevertheless, its actual calculation by means of modern many-body perturbation theory is weakened by the use of model Hamiltonians that are based on parameters difficult to extract from the experiments. Such shortcoming can be bypassed by using density-functional theory to evaluate the electron-phonon scattering amplitudes, phonon frequencies, and electronic bare energies. In this work, we discuss how a consistent many-body diagrammatic expansion can be constructed on top of density-functional theory. In that context, the role played by screening and self-consistency when all the components of the electron-nucleus and nucleus-nucleus interactions are taken into account, is paramount. A way to avoid overscreening is notably presented. Finally, we derive cancellation rules as well as internal consistency constraints in order to draw a clear, sound, and practical scheme to merge the many-body perturbation and density-functional theory.

NEEDS for LHC experiment planning from results of very high energy cosmic ray Investigations (NEEDS-2)

12 years ago, at 12 th ISVHECRI, a special NEEDS workshop was held to discuss future LHC data required for interpretation of cosmic ray experiments. Now, when the main task of LHC is solved – the Higgs boson is discovered – the question “What will be the next?” is very actual. In this paper the results of cosmic ray experiments at LHC energies are considered. Their possible explanation in the frame of a new model of production of quark-gluon matter blobs is discussed. The necessity to pass in LHC experiments from investigations of pp -interactions to investigations of nucleus-nucleus interactions is underlined since cosmic rays consist mainly of nuclei (≈ 60%) which interact with nuclei of air. But namely in these nucleus-nucleus interactions many unusual results were obtained in cosmic ray investigations. Corresponding tasks for future LHC experiments are proposed.

Azimuthally Integrated HBT Parameters for Charged Pions in Nucleus-Nucleus Interactions versus Collision Energy

The energy dependence of spatiotemporal characteristics of particle emission region is studied for charged pions produced in nuclear collisions. No dramatic change is observed for the HBT parameters with increasing of the center-of-mass (c.m.) energy per nucleon-nucleon pair,sNN, forsNNof a few GeV to a few TeV. The emission duration is obtained to be almost independent of the c.m. energy within the measurement uncertainties. The analytic function is suggested for a smooth approximation of the energy dependence of the main HBT parameters. The fits demonstrate reasonable agreement with the experimental data. Predictions are made for future LHC and FCC experiments.

Glauber Monte Carlo program for NICA/MPD and CBM experiments

A program code widely applied at RHIC and LHC for calculations of geometrical properties of nucleus-nucleus interactions is adapted for NICA/MPD and CBM energies. A parameterization of pp elastic scattering amplitude earlier proposed by the authors and valid at √s ≥ 3 GeV is used for a setting of the nucleon-nucleon collision profile. An approach well known in physics of low and intermediate energies is used for a determination of nuclear parameters. The code is enlarged by a possibility to account for the Gribov inelastic screening.

Scaling of charged particle production and centrality determination in p-Pb collisions at √sNN= 5.02 TeV at ALICE

Proton-nucleus collisions are studied in order to disentangle initial state effects, already present in cold nuclear matter, from final state effects, that are associated to the hot and strongly interacting medium created in A-A collisions. However, after the 2013 p-Pb data taking at LHC, the importance of p-A collisions on their own has been acknowledged. Several measurements clearly showed that p-A collisions cannot simply be explained by an incoherent superposition of proton-nucleon collisions, but indicate the presence of coherent and collective effects, with a strong dependence on the collision geometry. These measurements pointed out the need for a detailed characterization of the collision geometry.Typically, parameters such as the number of binary collisions N coll or the number of participating nucleons N part are used to characterize the centrality. In nucleus-nucleus interactions the centrality is usually estimated by measuring the charged particle multiplicity. However, in contrast to A-A, in p-A collisions the large fluctuations in a much reduced multiplicity environment generate a dynamical bias in centrality classes based on particle multiplicity measurement.The centrality determination is critically addressed and a different approach to extract the average N coll values, needed to compare p-A to pp data, is presented. The centrality dependence of primary charged-particle production and of transverse momentum distributions in p-A collisions at √s NN = 5.02 TeV measured by ALICE are presented.

Microscopic study of noncentral effects in heavy-ion fusion reactions with spherical nuclei

Fusion reactions of $^{16}\mathrm{O}+^{16}\mathrm{O},^{40}\mathrm{Ca}+^{40}\mathrm{Ca}$, and $^{40}\mathrm{Ca}+^{90}\mathrm{Zr}$ have been investigated by using the three-dimensional (3D) time-dependent Hartree-Fock approach with and without density constraint. The interaction potentials and effective mass parameters are studied. It is found that both the nucleus-nucleus interaction potentials and the effective mass parameters of these systems depend on the impact parameter. Such noncentral effects on fusion cross sections are also investigated. It is shown that the noncentral effect can reduce the fusion cross sections significantly when the incident energy is just above the barrier, while it becomes weaker with the increasing incident energy and can be totally neglected when the energy is up to twice as much as the barrier height in these spherical colliding systems.

Classical-trajectory Monte Carlo model calculations for the antiproton-induced ionization of atomic hydrogen at low impact energy

The three-body dynamics of the ionization of the atomic hydrogen by 30 keV antiproton impact has been investigated by calculation of fully differential cross sections (FDCS) using the classical trajectory Monte Carlo (CTMC) method. The results of the calculations are compared with the predictions of quantum mechanical descriptions: The semi-classical time-dependent close-coupling theory, the fully quantal, time-independent close-coupling theory, and the continuum-distorted-wave-eikonal-initial-state model. In the analysis particular emphasis was put on the role of the nucleus-nucleus (NN) interaction played in the ionization process. For low-energy electron ejection CTMC predicts a large NN interaction effect on FDCS, in agreement with the quantum mechanical descriptions. By examining individual particle trajectories it was found that the relative motion between the electron and the nuclei is coupled very weakly with that between the nuclei, consequently the two motions can be treated independently. A simple procedure is presented by which the NN interaction effect can be included into the calculations carried out without it.

Isotopic and neutron-excess effects in nucleus-nucleus interaction and fusion cross sections

The interaction potentials and fusion cross sections for various nickel and tin isotopes are calculated. The fusion cross sections are computed with allowance for coupling to the channels of low-lying 2+ and 3− vibrational states in the interacting nuclei. Good agreement with the experimental data is obtained. The isotopic dependences of interaction potentials and fusion cross sections of nuclei are analyzed in detail.

Quantitative analysis of precise heavy-ion fusion data at above-barrier energies using Skyrme-Hartree-Fock nuclear densities

We calculate the capture (fusion) cross sections for nine reactions involving spherical nuclei: $^{16}\mathrm{O}$ + $^{16}\mathrm{O}$, $^{28}\mathrm{Si}$, $^{92}\mathrm{Zr}$, $^{144}\mathrm{Sm}$, $^{208}\mathrm{Pb}$; $^{28}\mathrm{Si}$ + $^{28}\mathrm{Si}$, $^{92}\mathrm{Zr}$, $^{208}\mathrm{Pb}$; $^{32}\mathrm{S}$ + $^{208}\mathrm{Pb}$. For six of them precision data are available in the literature. Analysis of these precision data within the framework of the single-barrier penetration model based on the Woods-Saxon profile for the strong nucleus-nucleus interaction potential (SnnP) gave rise to the problem of the apparently large diffuseness of the SnnP [Newton et al., Phys. Rev. C 70, 024605 (2004)]. Our fluctuation-dissipation trajectory model is based on the double-folding approach with the density-dependent M3Y NN forces including the finite-range exchange part. For the nuclear matter density the Skyrme-Hartree-Fock approach including the tensor interaction is applied. The resulting nucleus-nucleus potential possesses rather small (normal) diffuseness. The strength of the radial friction ${K}_{R}$ is used as the free parameter of the model. It turns out that for four of the five reactions induced by $^{16}\mathrm{O}$ (except $^{16}\mathrm{O}$ + $^{208}\mathrm{Pb}$) the calculated cross sections cannot be brought into agreement with the data within the experimental errors. This suggests that the calculated nuclear density is incorrect for $^{16}\mathrm{O}$. For the reactions not involving $^{16}\mathrm{O}$ and, surprisingly, for the $^{16}\mathrm{O}$ + $^{208}\mathrm{Pb}$ reaction the agreement with the data within 2-5% is achieved at ${K}_{R}=1.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}$ to $3.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}\phantom{\rule{0.28em}{0ex}}{\mathrm{MeV}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}\mathrm{zs}$ which is in accord with the previous works.

Statistical theory of rarified gases in the coulomb model of substance: Adiabatic approximation and initial atoms

In the framework of the adiabatic approximation for a subsystem of nuclei with the average distance between them significantly exceeding the dimensions of the initial atom, we consider a nonrelativistic Coulomb system consisting of electrons and nuclei of one type for the temperature range where we can restrict ourself to using the ground state to describe the electron subsystem. We show that the equilibrium properties of such a system are equivalent to the thermodynamic properties of the one-component system of initial atoms interacting between themselves via a short-range potential that is the effective potential of the nucleus-nucleus interaction. In the framework of the applicability of Boltzmann statistics, we present quantum group expansions for the thermodynamic properties of a chemically reacting rarified gas that correspond to the method of initial atoms.