Nucleus-nucleus Interactions Research Articles

Exchange contributions to nucleus-nucleus potentials deduced from RGM phase shifts using inversion

Abstract We have determined, for certain representative cases, the representation in terms of local potentials of the contribution to the nucleus-nucleus interaction of one-nucleon exchange, core exchange and intermediate exchange terms. We do this by applying S l -to- V ( r ) inversion, using the IP method, to phase shifts from RGM calculations of Fujiwara and Tang, and LeMere et al. For tα at 18 MeV we find a shape parity dependence which is identical in nature to that found in other cases recently. For 3 He+ α at 60 MeV, a strong parity shape dependence still occurs, but of slightly different form. For α + 16 O, the 4N exchange generates a small parity dependence of the same nature, but this seems to disappear in the full RGM calculation. In the last two cases, we show the characteristic forms of potentials due to the different exchange terms. These calculations indicate the scope of inversion as a means of extracting information from microscopic calculations concerning the nucleus-nucleus interaction.

Multiplicities of charged particles in 3.7A GeV32S emulsion interactions

The interactions of 3.7A GeV32S ions in nuclear emulsion have been investigated. The multiplicities of charged particles emitted from both projectile and the target nuclei have been studied. The data are compared with current results on the interactions of relativistic ions with emulsion nuclei. The variation of the characteristics of the nucleus-nucleus interactions with the projectile mass number is investigated. The correlations between various kinds of particles of multiple production in32S-Em collisions are presented.

SOME FEATURES OF INELASTIC INTERACTIONS OF 28Si AND 12C IONS IN NUCLEAR EMULSION AT 4.5A GeV/c

Multiplicity distributions of various types of tracks produced in inelastic interactions of 28 Si and 12 C at 4.5A GeV/c with nuclear emulsion nuclei have been investigated. The correlations of the type <Ni(Nj)> where Ni, Nj=Ng, Nb, Nh or Ns with i≠j have been studied and compared with the results from p-Em interactions at the same momentum per nucleon. Some saturation effects in the values of <Nb> with Ng are observed. Furthermore, some of these correlations show almost similar dependence in nucleus-nucleus and proton-nucleus interactions at same per particle momenta. The values of <Ns> have been obtained by subtracting the contribution of Z=1 fragments to the observed showers. The dependence of <Ns> so obtained on the number of interacting projectile nucleons shows that the nucleus-nucleus collisions at these energies can be interpreted in terms of multiple N-N collisions.

Can weakly absorbing surface transparent nucleus-nucleus interaction ensure orbiting?

We find that in contrast to the large orbiting yield seen in $^{28}\mathrm{Si}$${+}^{12}$C, $^{24}\mathrm{Mg}$${+}^{16}$O, $^{24}\mathrm{Mg}$${+}^{12}$C, and $^{20}\mathrm{Ne}$${+}^{12}$C reactions, the back-angle, strongly damped binary yields from $^{4}\mathrm{He}$${+}^{27}$Al and $^{4}\mathrm{He}$${+}^{40}$Ca reactions are in agreement with the predictions of statistical compound nuclear reaction. These results disagree with the observation from heavy-ion reaction systematics that the orbiting yield will dominate whenever the number of open channels is small, and suggest that the weak absorption and surface transparency of nucleus-nucleus interaction are not sufficient conditions for the dominance of orbiting in back-angle, strongly damped reaction.

Study of the high energy cosmic ray cascades using the dual parton model

Abstract In this paper we describe an application of the two component dual parton model, for the simulation of high energy cosmic ray cascades. The DPMJET interaction model has been tuned to accelerator data for hadron-nucleus and nucleus-nucleus interactions, and its performance in the fragmentation region has been optimized. We make use of this generator inside the HEMAS shower code. Results are presented with particular emphasis on the electromagnetic component and on the high energy muon content of the showers.

Investigation of nucleus-nucleus interactions by means of emulsions exposed in pulsed magnetic fields of 30–50 T at the nuclotron

The data on the momentum spectra of energetically distinguished particles of a various nature for pN, pA interactions at 21 GeV/c and πN, πA interactions at 50 GeV/c are presented. Emulsions were first exposed in a pulsed magnetic field of 18 T. From comparison of the pN, πN and pA, πA data it follows that the behaviour of incident and newly generated particles in their passage through nuclear matter is different. The possibilities to study nucleus-nucleus interactions by means of emulsion exposures in pulsed magnetic fields of 30–50 T at the Nuclotron in Dubna are considered.

On slow-particle production in 200A GeV16O-emulsion interactions

The multiplicity distributions and the correlations of different types of slow particles produced in 200A GeV oxygen-induced interactions with emulsion nuclei are presented. The experimental distributions are studied within the framework of the generalized Andersson-Otterlund-Stenlund (AOS) model for nucleus-nucleus interactions. The generalized (AOS) model fails to describe the present experimental data. Also a systematic comparison using the calculations of VENUS model is made. The grey-particles multiplicity is successfully reproduced by the theoretical multistring model VENUS, while the model is inadequate for explaining the distribution of black particles.

Nuclear dependence of the Drell-Yan process in relativistic heavy ion collisions.

The EMC-type effects observed in lepton, hadron-nucleus collisions have revised the conventional high energy picture of the nucleus as a collection of semi-independent nucleons interacting via a meson field. For high momentum transfers deviations from this picture can be accounted for by a QCD treatment in which the nuclear dependence, attributed to overlapping of bound nucleons, is introduced through the nonperturbative parton momentum distributions. These phenomena must be more pronounced in nucleus-nucleus interactions to be studied at the Relativistic Heavy Ion Collider. We calculate the ratio of the Drell-Yan cross section for collisions of two large nuclei to that for interactions of two protons or deuterium nuclei to order [alpha][sub [ital s]]. We predict that in the invariant mass range between the heavy quarkonium peaks this ratio is less (greater) than one for small (large) values of the pair longitudinal and transverse momentum. For fixed nucleon energy the depletion at low lepton momenta decreases with increase of the invariant mass and disappears well beyond the meson resonances. We investigate the dependence of these effects on the choice of ocean and gluon momentum distributions.

CONTRIBUTION OF THE PARITY DEPENDENT POTENTIAL IN HEAVY ION TRANSFER REACTIONS

The theory of heavy ion reactions with particle transfer is considered in the framework of the exact finite-range distorted wave Born approximation (EFR-DWBA). Modified Woods-Saxon potentials which include a parity dependent interaction and an angular momentum absorptive term have been used as the ion-ion interactions in the initial and final channels. The bound state interactions are represented by nucleus-nucleus inter-actions which include repulsive and attractive Yukawa type components. The present numerical calculations of the differential cross-sections are in good agreement with the experimental measurements. The distorting parity dependent potentials are found very important in reproducing the cross-sections at backward as well as at intermediate angles. The obtained extracted values of the spectroscopic factors are reasonable.

Multiplicities of secondaries in nuclear interactions, induced by 20Ne, 40Ar and 56Fe nuclei at 0.1–0.5 GeV/nucleon

Multiplicities of various species of charged secondaries produced in inelastic interactions of 20Ne, 40Ar and 56Fe nuclei with emulsion nuclei at 0.1–0.5 GeV/nucleon have been measured. The data obtained are compared with the results for interactions of higher energy nuclei with emulsion nuclei. The dependences of the nucleus-nucleus interaction parameters on masses and energies of colliding nuclei are examined.

First results of the CERES electron pair spectrometer from p + Be, p + Au and S + Au collisions

The CERES experiment (CErenkov Ring Electron Spectrometer) studies the production of low mass e +e − pairs in proton-proton, proton-nucleus and nucleus-nucleus interactions at the CERN SPS. The CERES spectrometer, has a novel design based on two Ring Imaging Cherenkov (RICH) counters, and it operates close to its design specifications. Data were recorded with 200 GeV u sulfur beam and 450 GeV proton beam. The analysis is in progress. We have extracted first e + −-pairs samples for p+Be, p+Au and S+Au collisions. In addition other physics topics were addressed. Inclusive photon spectra were measured in S+Au interactions. No excess over known hadronic sources was found within our present systematic error of 11%. Results on high p i charged pion spectra are presented up to 4 GeV c . We also studied the production of e +e −-pairs m the strong electromagnetic fields of very peripheral S+Pt collisions. The data are well described by a first-order perturbative QED-calculation.

Somatic hybridization as a tool for tomato breeding

Protoplast fusion can be used to produce somatic hybrids of species that cannot be obtained by sexual hybridization. The possibility to introgress genes from Solanum species into the cultivated tomato species Lycopersicon esculentum, and to obtain novel cytoplasm-nucleus combinations (cybrids) was considered as an important strategy to extend the genetic variation available for tomato breeding. Somatic hybrids between L. esculentum and other Lycopersicon species, as well as between L. esculentum and Solanum or Nicotiana species, have been produced. Specific mutants, genotypes with antibiotic resistances, and metabolic inhibition by iodoacetate or iodoacetamide and irradiation were used for the selection of hybrids. In addition, the improvement of protoplast culture techniques and the use of the favourable tissue culture traits derived from species such as L. peruvianum, which have been introduced into tomato by classical breeding, allowed the efficient recovery of somatic hybrids. However, the occurrence of somatic incongruity in fusion combinations of L. esculentum and Solanum and even more in L. esculentum and Nicotiana, did not allow the production of true cybrids and/or fertile hybrids, indicating the importance of both cytoplasm-nucleus and nucleus-nucleus interactions in somatic incongruity. Another problem with fusions between distantly related species is the strongly reduced fertility of the hybrids and the very limited homoeologous recombination between chromosomes of the parental species. Partial genome transfer from donor to recipient through microprotoplast (+) protoplast fusion, and the production of monosomic or disomic chromosome addition lines, light overcome some of these problems. In symmetric somatic hybrids between L. esculentum and S. tuberosum the occurrence of limited somatic and meiotic recombination was demonstrated. Fertile progeny plants could be obtained, though at a low frequency, when embryo rescue was performed on a large scale after backcrossing hexaploid somatic tomato (+) potato hybrids with a tetraploid potato genotype. The potential value of genomic in situ hybridization (GISH) and RFLPs for the analysis of the genome/chromosome composition of the hybrids has been demonstrated for intergeneric somatic hybrids between Lycopersicon and Solanum.

The ALICE heavy-ion experiment at the CERN LHC

ALICE (A Large Ion Collider Experiment) is a dedicated heavy-ion detector designed to exploit the physics potential of nucleus-nucleus interactions at the LHC. As a general purpose experiment, it will allow a comprehensive study of hadrons, electrons, and photons produced in the collision of heavy nuclei, up to the highest particle multiplicities anticipated at the LHC. The central part of ALICE, which covers (90 ± 45)° (| η|< 0.9) over the full azimuth, is embedded in a large magnet with a weak solenoidal field. The base-line design consists (from inside out) of a high-resolution inner tracking system, a cylindrical TPC, a particle identification array (TOF or RICH detectors), and a single-arm electromagnetic calorimeter. Possible upgrades under study include large-acceptance electromagnetic calorimeters and a muon identification system. We will trigger on central collisions with a zero degree calorimeter and measure multiplicity distributions over a large fraction of the available phase space.

INTERMITTENCY PATTERNS IN PROTON-NUCLEUS INTERACTIONS AT HIGH ENERGY

A study of intermittency in hadron-nucleus and the comparison with nucleus-nucleus interactions is presented. The power law behavior of the factorial moments and the variation of intermittency index with the center-of-mass energy are shown. Results favor the formation of quark-gluon plasma in preference to a cascade mechanism.

Multifractal analysis of nucleus-nucleus interactions.

We have performed a multifractal ($G$-moment) analysis of 14.6-200 GeV/nucleon nucleus-nucleus and 200-800 GeV proton-nucleus interactions from KLM and Fermilab E-90 and E-508 emulsion data, including explicit corrections for the finite statistical sample. The corrected slopes of the $G$-moments for protons, $^{16}\mathrm{O}$, $^{28}\mathrm{Si}$, and $^{32}\mathrm{S}$ nuclei show only slight evidence for departures from random behavior, while the normalized entropies appear to show a more consistent departure from randomness, particularly for protons. Given the size of the uncertainties, the results of the fractal analysis are not inconsistent either with results of intermittency analyses for nucleus-nucleus collisions or with the nonrandom behavior previously reported for leptonic and hadronic collisions. However, because of the effects of statistical noise, the fractal analysis is not as sensitive as the intermittency analysis for detecting nonrandom fluctuations.

Evidence of Different Pion Coherence Zone in High Energy Hadron-Nucleus and Nucleus-Nucleus Interactions

This paper reports detailed observation of coherent production of pions in hadron-nucleus interactions at 200 to 400 GeV/c and nucleus-nucleus interactions at 2.1 to 4.5 GeV/c per nucleon. The analysis is based on a comparative study of experimental multiplicity distribution in different pseudorapidity bins with Poissonian and Chaotic distributions.

Evidence of Different Pion Coherence Zone in High Energy Hadron-Nucleus and Nucleus-Nucleus Interactions

This paper reports detailed observation of coherent production of pions in hadron-nucleus interactions at 200 to 400 GeV/c and nucleus-nucleus interactions at 2.1 to 4.5 GeV/c per nucleon. The analysis is based on a comparative study of experimental multiplicity distribution in different pseudorapidity bins with Poissonian and Chaotic distributions

The investigation of energy spectra of pi - mesons at fixed angles in nucleus-nucleus interactions at a momentum of 4.5 GeV c-1 per incident nucleon

The energy spectra of pi - mesons emitted in an angular interval of 0<or= theta lab<or=180 degrees in the laboratory system in He-Li, He-C, C-Ne, Mg-Mg, C-Cu, C-Pb and O-Pb collisions at a momentum of P=4.5 GeV c-1 per incident nucleon have been investigated. The spectra of pi - mesons depend exponentially on their kinetic energy. The values of slope parameter T0 are weakly dependent on atomic numbers of projectile (Ap) and target (AT) nuclei for angles theta lab(90 degrees and independent for theta lab)90 degrees . The shape of spectra in laboratory and CM systems for all colliding pairs does not depend on Ap, AT. The slope parameter 1/T0 depends on the pi - mesons' emission angle. This cos theta 1ab dependence is nonlinear. There is an indication that the internal energy of the cluster from which the pi - mesons are emitted depends weakly on Ap, AT.

Subthreshold meson production in nuclear reactions

The empirical knowledge about subthreshold meson production in proton-nucleus and nucleus-nucleus interactions is reviewed. The possibility to obtain information about the conditions in the early phase of a heavy ion reaction, where compression could be expected, is discussed.

Can ultrarelativistic heavy nuclei produce Centauro events?

Negative results of experimental searches for heavy penetrating particles at mountain tops impose strong constraints on the model of Panagiotou, Petridis, and Vassiliou for the production of Centaurotype cosmic-ray events by way of nucleus-nucleus interactions in the upper atmosphere. The quarkmatter fireball postulated to produce Centauros must have bizarre properties---an interaction mean free path of \ensuremath{\sim}200 g ${\mathrm{cm}}^{\ensuremath{-}2}$ and a proper lifetime of \ensuremath{\sim}${10}^{\ensuremath{-}7}$ s for an object with $A\ensuremath{\approx}50$.