A. Palmeri

Evidence of a two-source emission for light charged particles in coincidence with pions produced in 16O + 27Al collisions at 94 MeV/nucleon

Abstract H and He ions have been detected in coincidence with charged pions in the reaction induced by 16O on 27Al target at 94 MeV/u incident energy. We analyse velocity spectra and cross sections of He ions emitted in the angular range 4°–150° in coincidence with charged pions detected at 90°. A two-source emission mechanism of the helium particles and a pion statistical production from an equilibrated participant zone is stressed. The absolute yields at different angles are compared with results of a theoretical model for medium energy heavy-ion reactions in the framework of a participant-spectator picture.

A study for the use of the LNS crystal ball multidetector as a neutral pions spectrometer

Abstract The response of the large BaF2 multidetector Crystall Ball to high energy photons and neutral pions was studied by simulations carried out with the code GEANT3. The properties of the detector relevant to π0 detection, such as resolution, linearity and efficiency are discussed. The performance of the system can be improved by considering a cluster of 8 detectors around the illuminated one to follow the development of the electromagnetic shower. As a π0 spectrometer the Crystal Ball covers the whole angular range and permits the detection of π0s over 100 MeV kinetic energy. Estimated π0 efficiencies vary between 60% for pio emitted at rest to 35% at 100 MeV kinetic energy.

16O breakup on Al, Ni and Au targets at 94 MeV/nucleon

Abstract The HeHeHeHe disassembly channel of the 16O on 27Al, 58Ni and 197Au targets has been studied at 94 MeV/nucleon. Charged particles have been detected by a multielement array of plastic scintillators covering the zenithal angular domain between 3° and 30° and the total azimuthal one. Standard relativistic kinematics has been used to reconstruct the excitation energy of the primary projectile-like nucleus. Mean values of the excitation energy are found independent of the target mass. The comparison with data taken at lower bombarding energies is compatible with a saturation of the mean excitation energy.

Light fragment emission correlated with large transverse momentum protons in 94 mev/u 16O induced reactions

Abstract Angular, multiplicity and velocity distributions as well as azimuthai asymmetries of light fragments (Z = 1 and 2) correlated with large transverse momentum protons detected at 90° have been measured in 16O + 27Al collisions at 94 MeV/u. Data are compared with a model based on the standard high-energy fireball geometry coupled with the Weisskopf theory of evaporation. Reasonable agreement is achieved with the exception of some discrepancies which could arise either from the absence of specific intermediate-energy corrections or from a non-statistical process.

Neural tracking in ALICE

A neural network based algorithm to perform track recognition in the ALICE Inner Tracking System (ITS) for high transverse momentum particles (pt > 1 GeV=c) is presented,. The model is based on the Denby-Peterson scheme, with some original improvements which are necessary to cope with the very high track density expected in ALICE. Results are shown for a central Pb–Pb event at 5.5 A TeV in the center of mass system and the comparison with the Kalman Filter results is included. r 2003 Elsevier Science B.V. All rights reserved. PACS: 84.35.+i

Semi exclusive pion production by heavy-ions at energy below 100 MeV/u

Abstract Charged pions have been measured in the reactions 12 C + 12 C and 27 Al + 16 O at 84 and 94 MeV/u respectively, in coincidence with charged fragments detected at forward angles by a large area multidetector. Multiplicities and velocities of fragments in coincidence with pions are, respectively, higher and lower than the inclusive ones.

Measurement of the Dalitz decay of π0 produced in heavy ion collisions at intermediate energies

Abstract An experimental search for events with three electromagnetic showers originating from the Dalitz decay of the π 0 meson ( π 0 → γe + e − ) has been carried out using a BaF 2 multidetector array covering a large fraction of the overall solid angle in an experiment where the main decay mode π 0 → γγ was measured at the same time. Neutral pions were produced in the reaction 36 Ar + 27 Al at 3.4 GeV laboratory incident energy. Identification of the π 0 3-body decay was achieved by an invariant mass analysis after a selection of the events. A branching ratio Γ ( γ e + e − )/ Γ (2 γ ) = (1.32 ± 0.11) × 10 −2 was deduced.

Subthreshold pion production from nucleus-nucleus collisions around 100 MeV/nucleon

Several global variables were tested with the aim to determine the impact parameter in nucleus-nucleus collisions producing pions at incident energies around 100 MeV/nucleon. The experimental set-up includes the MEDEA multidetector, part of which is used as aπ0 spectrometer, and an additional hodoscope of plastic scintillators to cover very forward angles. A statistical model was used to generate bothinclusive and pion-triggered events. Selection ofwell measured events was made through the measured total parallel momentum. Among the different global variables which were tested, the average parallel velocity was seen to give the best correlation with the impact parameter.

Energetic Particle Emission in Heavy-Ion Collisions Around 100 MeV/u

Strong similarities between high-energy proton and subthreshold pion production at large angles in heavy-ion collisions around 100 MeV/u are evidenced. In both cases, light charged particles emitted in coincidence with the pion or the proton exhibit the same features. In addition, by considering the particles (pion or proton) irrespective of their nature and only characterized by the total energy needed for their production, we find that the process is dominated by phase space constraints.

Detection of η mesons in heavy-ion collisions at 100 MeV/nucleon

Abstract A study of the detection of η mesons in heavy-ion collisions at 100 MeV/nucleon by a large array of BaF 2 modules has been carried out using full GEANT3 simulations. The most probable decay modes of the η mesons have been considered. Invariant mass spectra from the detection of two or more electromagnetic showers are discussed. The different sources of contamination are evaluated. The detection limits in terms of production cross section are discussed. An analysis of experimental data taken at 95 MeV/nucleon with the MEDEA array showed a few events which are compatible with the η → γγ decay.