Pion radii in nonlocal chiral quark model

The electromagnetic radius of the charged pion and the transition radius of the neutral pion are calculated in the framework of the nonlocal chiral quark model. It is shown in this model that the contributions of vector mesons to the pion radii are noticeably suppressed in comparison with a similar contribution in the local Nambu--Jona-Lasinio model. The form-factor for the process gamma*pi+pi- is calculated for the -1 GeV^2<q^2<1.6 GeV^2. Our results are in satisfactory agreement with experimental data.Comment: 7 pages, 7 figure

New method for the discrimination of single-source events in heavy-ion collisions

Matière NucléaireThis paper introduces a new method for the selection of central single-source events, based on classical multivariate techniques. The resulting discriminating variable is shown to be valid for different hypotheses on the nuclear source deexcitation mechanism. It enables the selection of events which are representative of the whole set of single-source events. Application to the Ni+Ni at 32A MeV system measured with the INDRA multidetector has allowed the determination of the fusion probability as a function of the impact parameter and the evaluation of the corresponding cross section

Is reducibility in nuclear multifragmentation related to thermal scaling?

International audienceThermal scaling (Arrhenius law for an “elementary” probability p of binomial function) and reducibility in intermediate mass fragments (IMF's) production are examined for data of the reaction 129Xe+ natSn at 50 MeV/u. The study of the longitudinal velocities and of the average transverse energies of the IMF's contradicts the assumption that the total transverse energy of all detected particles Et is related to a well defined temperature

Directed and elliptic flow in Au + Au at intermediate energies

Directed and elliptic flow for the Au + Au system at incident energies between 40 and 150 MeV per nucleon has been measured using the INDRA 4 pi multi-detector. For semi-central collisions, the elliptic flow of Z <= 2 particles switches from in-plane to out-of-plane enhancement at around 100 MeV per nucleon, in good agreement with the result reported by the FOPI Collaboration. The directed flow changes sign at a bombarding energy between 50 and 60 MeV per nucleon and remains negative at lower energies. The conditions for the appearance and possible origins of negative flow are discussed

Digital filtering: a common analysis for data and mean field theories in heavy-ions collisions at intermediate energy

Matière Nucléaire, GANIL E209b, GANIL E210International audienceTo select well-defined event configurations from heavy-ion collisions in the Fermi energy domain, a digital filtering technique of the charge density distribution along the deflection axis in the velocity space is presented. Charge density appears as a robust variable and can be used for a quantitative comparison of experimental data obtained with 4π arrays and mean-field transport equation predictions

Directed and elliptic flow in 197Au+197Au^{197}Au+^{197}Au at intermediate energies

Directed and elliptic flow for the $^{197}$Au+$^{197}$Au system at incident energies between 40 and 150 MeV per nucleon has been measured using the INDRA 4$\pi$ multi-detector. For semi-central collisions, the excitation function of elliptic flow shows a transition from in-plane to out-of-plane emission at around 100 MeV per nucleon. The directed flow changes sign at a bombarding energy between 50 and 60 MeV per nucleon and remains negative at lower energies. Molecular dynamics calculations (CHIMERA) indicate sensitivity of the global squeeze-out transition on the $\sigma$ and demonstrate the importance of angular momentum conservation in transport codes at low energies. The conditions for the appearance and possible origins of negative flow are discussed