Nucleus-nucleus Interactions Research Articles

Multiparticle production in nucleus-nucleus interaction at 2.1 GeV/n and 200 GeV/n. Four-momentum transfer analysis

This paper presents an analysis of the four-momentum transfer between the fireballs in the events produced in16O-AgBr interactions at 2.1AGeV and 60AGeV, and32S-AgBr interaction at 200A GeV. It also reveals the correlation between average four-momentum transfer and multiplicity of shower particles, and also the distribution of four-momentum transfer.

Nonclassical Field States in Quantum Optics and Particle Physics

The primary aim of the present paper is to draw the attention of particle physicists to new developments in studying squeezed and correlated states of the electromagnetic field, and those working on the latest developments to new findings about multiplicity distributions and other specific effects in quantum chromodynamics. New types of nonclassical states used in quantum optics such as squeezed states, correlated states, and even and odd coherent states (Schrodinger cat states) for one-mode and multimode interactions are reviewed. Their distribution functions are analyzed according to the method first used for multiplicity distributions in high-energy particle interactions. The phenomenon of oscillations of particle distribution functions of squeezed fields is described and related to the phenomenon of oscillations of cumulant moments of some distributions for squeezed and correlated field states. Possible extension of the method to fields different from the electromagnetic field (gluons, pions, etc.) is conjectured, and some predictions of specific effects in nucleus-nucleus interactions at high energies are presented.

Nonlocal effects in the8Bebreakup

A collective Hamiltonian for a two alpha particles aggregate, which describes the ${}^{8}\mathrm{Be}$ nucleus, encompassing a collective potential and an inertia function of that system, is obtained and analyzed through the use of a technique --- derived from an approach of the generator coordinate method (GCM) --- which allows for the extraction of collective information. The nucleon-nucleon interaction considered here is the one proposed by Volkov plus the Coulomb repulsion. It is shown that nonlocal effects appear in those collective functions describing the spontaneously occurring breakup process. Furthermore, the result for the inertia function stands for a microscopically generated evidence supporting a double-folding-based model of the real part of the nucleus-nucleus nonlocal interaction recently proposed.

A Rigidity Measurement of Pseudo-Rapidity Spectrum of Produced Particles in High Energy Nucleus-Nucleus Collisions

A new concept, rigidity of pseudo-rapidity spectrum, is extended into the study of the multiplicity fluctuations in high energy nucleus-nucleus interactions. In using the novel method to analyze the data of 16O-Em at 14.6, 60, and 200 A GeV, and 32S-Em at 200 A GeV, it is found that the rigidity of pseudo-rapidity spectrum in the central domain of pseudo-rapidity might be a mixture of Poisson type and Wigner one.

Mass spectrum of the temperature dependent Bethe-Salpeter equation for composites of quarks with a Coulomb plus a linear kernel

We assume that high-energy nucleus-nucleus interactions give rise to a hot and dense plasma comprising quarks and gluons due to successive nucleon-nucleon collisions. We treat this plasma as an ideal fluid at temperature T prior to its eventual particlization, and attempt a microscopic description of meson-formation by using finite temperature propagators for q and ¯q in a Bethe-Salpeter equation with a Coulomb plus a linear kernel. The equation thus obtained is reduced to a Schrodinger-like equation which then yields, for 0 < T < 86 MeV, the bound state masses for different states of b¯b and c¯c, which are in agreement with the experimental values for these states. The effects of the temperature of the plasma on the meson masses show up only when the temperature exceeds 86 MeV, pointing to the probable reason for the successes of the earlier models which did not explicitly take the temperature of the plasma into account.

Nucleus-nucleus collisions: what we have learned from the heavy ion program at CERN

In the first part, I give a brief description of the quark-gluon plasma search at CERN and of some experimental results. In the second part, I review a dynamical model of nucleus-nucleus interactions and propose a physical interpretation of those results.

Nonlocal Description of the Nucleus-Nucleus Interaction

The mean field interaction between complex quantum many-body systems (nucleus-nucleus, cluster-cluster, etc.) is still an open question in current physics research. The study of this matter is a fundamental step in the understanding of many-body dynamics. In the nucleus-nucleus case, significant progress has been achieved concerning this question during the last decade [1], as a consequence of the measurement of accurate and extensive elastic scattering data at intermediate energies. Nuclear rainbow scattering, first observed in a systems [2 ‐4] and later in light heavy ions [5 ‐ 7], probes the nucleus-nucleus potential not only at the surface region but also at smaller distances, and ambiguities in the real part of the potentials have been removed. The resulting phenomenological interactions have significant dependence upon the bombarding energies. Some theoretical models have been developed to account for this energy dependence through realistic mean field potentials. Nowadays, the most successful models seem to be those based on the DDM3Y interaction [8 ‐ 10] which is an improvement of the originally energyindependent double-folding potential [11]. But, in order to fit the data, the density- and energy-dependent DDM3Y potential needs a renormalization factor which besides being system dependent [1,12] is still slightly energy dependent [1]. In this Letter we show, by an extensive description of elastic scattering data using an optical integro-differential equation, that the dependence on the bombarding energy of the real bare potential is mostly due to the intrinsically nonlocal nature of the effective one-body interaction. The real bare potential (by bare we mean the average, mean field, interaction with no coupled channels effects) is constructed using the folding model. It contains no adjustable parameters and is energy independent. The absorptive part is taken to be a three parameters WoodsSaxon interaction. We also supply a simple approach to obtain the local-equivalent energy-dependent potential. Before we set the stage for the analysis of elastic scattering data, we first describe our theoretical model. When dealing with nonlocal interactions, one is required to solve the integro-differential equation 2 ¯ h 2

Evidence of scaling of void probability in nucleus-nucleus interactions at few GeV energy

The rapidity gap probability in the ${}^{24}\mathrm{M}\mathrm{g}\ensuremath{-}\mathrm{A}\mathrm{g}\mathrm{B}\mathrm{r}$ interaction at $4.5\mathrm{GeV}/c/\mathrm{nucleon}$ has been studied in detail. The data reveal scaling behavior of the void probability in the central rapidity domain which confirms the validity of the linked-pair approximation for the $N$-particle cumulant correlation functions. This scaling behavior appears to be similar to the void probability in the Perseus-Pisces supercluster region of galaxies.

Moment analysis, multiplicity distributions and correlations in high energy processes: nucleus-nucleus collisions

Cumulant oscillations, or $H_q$ moment oscillations, appear if the KNO multiparticle distribution decreases at large z, $z\equiv n/ <n>$, faster than the exponential, $exp(-D z^\mu)$, with $\mu > 1$. In nucleus-nucleus interactions this behaviour is related to the limitation in the average number of elementary central collisions (or average number of strings centrally produced), due to the finite number of nucleons involved. Colour deconfinement, via percolating string fusion, will drastically decrease the fraction of centrally produced strings and increase the cut-off parameter $\mu$: Moment oscillations will be displaced to smaller q and the width of the KNO distribution and forward-backward particle correlations will become smaller.

Deviations from the superposition model in a dual parton model with formation zone cascade in both projectile and target nuclei

A Formation Zone Intranuclear Cascade in the spectators of both projectile and target nuclei has been inserted in the DPMJET-II MC code. The hadrons produced in the intranuclear cascade contribute to Feynman-xF distributions in the fragmentation regions of target and projectile. We discuss the differences of this model with respect to the superposition model, as far as nucleus-nucleus interactions and the calculation of cosmic ray cascades are concerned.

Possible detection of quantum-mechanical interferences between gravitational forces and nucleus-nucleus Coulomb forces

We report on possible effects of quantum-mechanical interferences between gravitational forces and the nucleus-nucleus Coulomb interaction. We show that, although very small, these effects could be measured on using low-energy scattering between identical heavy nuclei. For the system ${}^{208}\mathrm{Pb}{+}^{208}\mathrm{Pb}{(E}_{L}=5\mathrm{MeV})$. The angular precision needed would be about $0.001\ifmmode^\circ\else\textdegree\fi{}$.

Characteristics of \pi^{-} Mesons Produced in Nucleus-Nucleus Interactions at Energy of 3.7 GeV Per Nucleon

The data are obtained on streamer chamber spectrometer SKM-200 at energy of 3.7 GeV per incident nucleon. From the analysis of angular distributions of \pi^{-} mesons the anisotropy coefficient a for He-Li, He-C, C-Ne, C- Cu, C-Pb, O-Pb and Mg-Mg collisions are obtained. It has been shown, that a is similar for symmetric system of nuclei (He-Li and Mg-Mg) and increases slowly with mass numbers of projectile (A_{p}) and target (A_{ T}) for other pairs of nuclei. The anisotropy coefficient a increases linearly with the kinetic energy E^{\ast}_{kin} (in c.m.s) for all pairs of nuclei. The qualitative agreement of our results with the predictions of the intranuclear cascade models has been observed.

Production of antiprotons in the upper atmosphere by interacting primary cosmic rays.

We calculate the p\ifmmode\bar\else\textasciimacron\fi{} background in the upper atmosphere which results when primary cosmic rays interact with air nuclei. Since the p\ifmmode\bar\else\textasciimacron\fi{} yield from p-nucleus and nucleus-nucleus interactions is not directly known from experiments, we derive these quantities by using a Monte Carlo simulation which is theoretically based on the dual parton model and which had been successfully applied to the description of hadron production in high energy collisions. Results on the calculated atmospheric p\ifmmode\bar\else\textasciimacron\fi{} background indicate a larger p\ifmmode\bar\else\textasciimacron\fi{} background than earlier estimates predicted, particularly at low energies. \textcopyright{} 1996 The American Physical Society.

Fluctuation study of pionisation in ultrarelativistic nucleus-nucleus interaction

The scaled factorial moments and the multifractal moments have been investigated in differentη-intervals to study the dynamical fluctuation of pions produced in 200 AGeV32S-Ag/Br interaction. In order to investigate the detail characteristics of intermittency behaviour, theF-moments are extracted up to the eighth order of moments in differentM-intervals. The analysis indicates a non-thermal phase transition and different regime of particle production during the hadronisation process.

High-multiplicity lead-lead interactions at 158 GeV/cper nucleon

The Krakow-Louisiana-Minnesota-Moscow Collaboration (KLMM) has exposed a set of emulsion chambers with lead targets to a 158 GeV/c per nucleon beam of Pb-208 nuclei, and we report the initial analysis of 40 high-multiplicity Pb-Pb collisions. To test the validity of the superposition model of nucleus-nucleus interactions in this new regime, we compare the shapes of the pseudorapidity distributions with FRITIOF Monte Carlo model calculations, and find close agreement for even the most central events. We characterize head-on collisions as having a mean multiplicity of 1550 +/- 120 and a peak pseudorapidity density of 390 +/- 30. These estimates are significantly lower than our FRITIOF calculations.

Determination of temperature and transverse flow velocity at chemical freeze-out in relativistic nuclear interactions.

We propose a parameter-free method to determine the temperature of a thermalized state in relativistic nuclear interactions, using the experimental ${\mathrm{\ensuremath{\mu}}}_{\mathit{q}}$/T and ${\mathrm{\ensuremath{\mu}}}_{\mathit{s}}$/T values, obtained from strange particle ratios. The hadron gas formalism and strangeness neutrality are employed to relate the quark-chemical potential ${\mathrm{\ensuremath{\mu}}}_{\mathit{q}}$ and ${\mathrm{\ensuremath{\mu}}}_{\mathit{s}}$ to the temperature and thus determine its value at chemical freeze-out. This temperature, together with the inverse slope parameter from ${\mathit{m}}_{\mathit{T}}$ distributions, enable the determination of the transverse flow velocity of the fireball matter, thus disentangling the thermal and flow effects. We study several nucleus-nucleus interactions from AGS and SPS and obtain the temperature, transverse flow velocity, and quark-chemical potentials. Extrapolating the systematics we predict the values of these quantities for ongoing and future experiments at AGS, SPS, and RHIC. We discuss the possibility of reaching the conditions for quark deconfinement and QGP formation and give distinct and identifiable signature. \textcopyright{} 1996 The American Physical Society.

The production of residual nuclei in peripheral high energy nucleus-nucleus interactions

A formation zone intranuclear cascade model is applied to peripheral nucleus-nucleus collisions. We calculate the excitation energies of prefragments, treat their further nuclear disintegration and introduce a model for nuclear deexcitation by photon emission. Results are compared to data on target associated particle production in nucleus-nucleus collisions. We discuss implications of these models to the description of particle production in the fragmentation regions. Special emphasis is put on applications for air showers induced by cosmic ray nuclei and for residual nucleus production at heavy ion colliders.

The study of angular distributions of pi - mesons in nucleus-nucleus interactions at a momentum of 4.5 GeV/c per nucleon

Data were obtained using the streamer chamber spectrometer SKM-200 at a momentum of 4.5 GeV/c per incident nucleon. From the analysis of angular distributions of pi - mesons the anisotropy coefficient a for He-Li, He-C, C-Ne, C-Cu, C-Pb, O-Pb and Mg-Mg collisions was obtained. It has been shown that a is similar for symmetric systems of nuclei (He-Li and Mg-Mg) and increases slowly with mass numbers of projectile (Ap) and target (AT) for other pairs of nuclei. The anisotropy coefficient a increases linearly with the kinetic energy E*kin (in the CMS) for all pairs of nuclei. The qualitative agreement of our results with the predictions of the intranuclear cascade models has been observed.

On the application of wavelet analysis to separation of secondary particles from nucleus-nucleus interactions

We apply wavelet analysis for separation of secondary particles from different channels of the d+Au→… reaction. Using the data obtained in the experiments at Nuclotron (Dubna) in March 1994 at a deuteron momentum of 3.8 GeV/c, we found 4 different regions in the time-of-flightvs. energy loss plot.

Comparative experimental study of the mirror 13N+12C and 13C+12C elastic scatterings.

The $^{13}\mathrm{N}$ + $^{12}\mathrm{C}$ and $^{13}\mathrm{C}$ + $^{12}\mathrm{C}$ elastic cross sections are measured at the center-of-mass energies of 7.8, 9.6, and 14.2 MeV, using radioactive $^{13}\mathrm{N}$ and stable $^{13}\mathrm{C}$ beams and position-sensitive solid-state detectors. These data are analyzed with the optical model assuming the same real central part of the nuclear potential for both systems as suggested by charge symmetry. The $^{13}\mathrm{N}$ + $^{12}\mathrm{C}$ angular distributions display a significant backward rise which arises from a parity dependence of the nucleus-nucleus interaction, as for the mirror $^{13}\mathrm{C}$ + $^{12}\mathrm{C}$ system. The corresponding parity terms in both potentials are similar when the different charges of the exchanged nucleons and their different binding energies are properly taken into account. A smaller imaginary part is obtained for $^{13}\mathrm{N}$ + $^{12}\mathrm{C}$ than for $^{13}\mathrm{C}$ + $^{12}\mathrm{C}$, which might be due to a smaller number of open two-body inelastic and direct reaction channels.