Abstract
The study of heavy ion collisions, with the help of such efficient multi-detectors as INDRA, has shown the persistence of reactions leading to single-source events, up to bombarding energies higher than the Fermi one. These events could help characterizing an expected phase transition in nuclear matter. Whatever interesting they may be, the single-source events correspond to a small part of the total cross section, which makes them difficult to isolate and therefore to analyze. That is why different selection means have been tested - thanks to the 'Simon' event generator - on a simulated Ni + Ni at 32 A·MeV sample, before any application to the INDRA experimental data. As the known methods based on global variables did not prove effective, a set of new 4-dimensional quantities has been built, whose main advantage lies in a better description of physical events. From a Discriminant Analysis performed on 625 of these new 'moments' proceeds a highly discriminant variable, called D{sub 625}. The experimental cross section associated with D{sub 625}-selected single-source events amounts to 170 mb at 32 A·MeV. Such quasi-fusion events are shown to disappear at about 60 A·MeV. As regards the deexcitation mode of the 32 A·MeV Ni + Ni
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Maskay-Wallez, Anne-Marie
[1]
- Inst. de Physique Nucleaire, Lyon-1 Univ., 69 - Villeurbanne (France)
Citation Formats
Maskay-Wallez, Anne-Marie.
New method for selection and characterization of single-source events in Ni+Ni collisions at 32 A.MeV; Nouvelle methode de selection et caracterisation des evenements monosource dans les collisions Ni+Ni a 32 A.MeV.
France: N. p.,
1999.
Web.
Maskay-Wallez, Anne-Marie.
New method for selection and characterization of single-source events in Ni+Ni collisions at 32 A.MeV; Nouvelle methode de selection et caracterisation des evenements monosource dans les collisions Ni+Ni a 32 A.MeV.
France.
Maskay-Wallez, Anne-Marie.
1999.
"New method for selection and characterization of single-source events in Ni+Ni collisions at 32 A.MeV; Nouvelle methode de selection et caracterisation des evenements monosource dans les collisions Ni+Ni a 32 A.MeV."
France.
@misc{etde_20035578,
title = {New method for selection and characterization of single-source events in Ni+Ni collisions at 32 A.MeV; Nouvelle methode de selection et caracterisation des evenements monosource dans les collisions Ni+Ni a 32 A.MeV}
author = {Maskay-Wallez, Anne-Marie}
abstractNote = {The study of heavy ion collisions, with the help of such efficient multi-detectors as INDRA, has shown the persistence of reactions leading to single-source events, up to bombarding energies higher than the Fermi one. These events could help characterizing an expected phase transition in nuclear matter. Whatever interesting they may be, the single-source events correspond to a small part of the total cross section, which makes them difficult to isolate and therefore to analyze. That is why different selection means have been tested - thanks to the 'Simon' event generator - on a simulated Ni + Ni at 32 A·MeV sample, before any application to the INDRA experimental data. As the known methods based on global variables did not prove effective, a set of new 4-dimensional quantities has been built, whose main advantage lies in a better description of physical events. From a Discriminant Analysis performed on 625 of these new 'moments' proceeds a highly discriminant variable, called D{sub 625}. The experimental cross section associated with D{sub 625}-selected single-source events amounts to 170 mb at 32 A·MeV. Such quasi-fusion events are shown to disappear at about 60 A·MeV. As regards the deexcitation mode of the 32 A·MeV Ni + Ni single-source events, an extensive experimental study and comparisons of the data with two reference models seem to confirm the hypothesis of a transition between fusion-evaporation and simultaneous multifragmentation mechanisms. (author) [French] L'etude des collisions d'ions lourds grace a des multidetecteurs tres performants, tels INDRA, a demontre la persistance, dans le domaine des energies intermediaires, de reactions dont les produits detectes proviennent d'un emetteur unique (monosource). Ces evenements constitueraient notamment un indicateur precieux d'une eventuelle transition de phase de la matiere nucleaire. Neanmoins, pour des energies de faisceau variant de 30 a 100 A-MeV, les monosources sont difficilement separables des evenements binaires (a deux sources), qui representent la majeure partie de la section efficace totale de la reaction. Dans le cas des donnees Ni+Ni a 32 A.MeV recueillies par INDRA, differentes methodes de selection connues, basees sur des variables globales communement employees, ont ete passees en revue a l'aide du generateur d'evenements SIMON. La separation monosources/Bisources obtenue ne se revelant pas entierement satisfaisante, un autre procede de discriminiation a ete applique: l'Analyse Factorielle Discriminante. Pour optimiser l'action de cette derniere, des variables globales originales (moments quadridimensionnels), conservant la quasi-totalite de l'information experiementale, ont ete utilisees. La section efficace des monosources isolees par cette nouvelle methode vaut environ 170 mb. Une etude aux autres energies faisceau disponibles permet de situer le seuil de disparition de ces evenements autour de 60 A.MeV. La caracterisation purement experimentale, a 32 A.MeV, de l'echantillon ainsi selectionne semble indiquer que la desexcitation de la source unique s'apparente a un processus d'emission sequentielle. La comparaison des donnees avec des modeles de reference, bases respectivement sur la multifragmentation et la decroissance sequentielle, tend, quant a elle, a prouver la coexistence des deux mecanismes de desexcitation.}
place = {France}
year = {1999}
month = {Jul}
}
title = {New method for selection and characterization of single-source events in Ni+Ni collisions at 32 A.MeV; Nouvelle methode de selection et caracterisation des evenements monosource dans les collisions Ni+Ni a 32 A.MeV}
author = {Maskay-Wallez, Anne-Marie}
abstractNote = {The study of heavy ion collisions, with the help of such efficient multi-detectors as INDRA, has shown the persistence of reactions leading to single-source events, up to bombarding energies higher than the Fermi one. These events could help characterizing an expected phase transition in nuclear matter. Whatever interesting they may be, the single-source events correspond to a small part of the total cross section, which makes them difficult to isolate and therefore to analyze. That is why different selection means have been tested - thanks to the 'Simon' event generator - on a simulated Ni + Ni at 32 A·MeV sample, before any application to the INDRA experimental data. As the known methods based on global variables did not prove effective, a set of new 4-dimensional quantities has been built, whose main advantage lies in a better description of physical events. From a Discriminant Analysis performed on 625 of these new 'moments' proceeds a highly discriminant variable, called D{sub 625}. The experimental cross section associated with D{sub 625}-selected single-source events amounts to 170 mb at 32 A·MeV. Such quasi-fusion events are shown to disappear at about 60 A·MeV. As regards the deexcitation mode of the 32 A·MeV Ni + Ni single-source events, an extensive experimental study and comparisons of the data with two reference models seem to confirm the hypothesis of a transition between fusion-evaporation and simultaneous multifragmentation mechanisms. (author) [French] L'etude des collisions d'ions lourds grace a des multidetecteurs tres performants, tels INDRA, a demontre la persistance, dans le domaine des energies intermediaires, de reactions dont les produits detectes proviennent d'un emetteur unique (monosource). Ces evenements constitueraient notamment un indicateur precieux d'une eventuelle transition de phase de la matiere nucleaire. Neanmoins, pour des energies de faisceau variant de 30 a 100 A-MeV, les monosources sont difficilement separables des evenements binaires (a deux sources), qui representent la majeure partie de la section efficace totale de la reaction. Dans le cas des donnees Ni+Ni a 32 A.MeV recueillies par INDRA, differentes methodes de selection connues, basees sur des variables globales communement employees, ont ete passees en revue a l'aide du generateur d'evenements SIMON. La separation monosources/Bisources obtenue ne se revelant pas entierement satisfaisante, un autre procede de discriminiation a ete applique: l'Analyse Factorielle Discriminante. Pour optimiser l'action de cette derniere, des variables globales originales (moments quadridimensionnels), conservant la quasi-totalite de l'information experiementale, ont ete utilisees. La section efficace des monosources isolees par cette nouvelle methode vaut environ 170 mb. Une etude aux autres energies faisceau disponibles permet de situer le seuil de disparition de ces evenements autour de 60 A.MeV. La caracterisation purement experimentale, a 32 A.MeV, de l'echantillon ainsi selectionne semble indiquer que la desexcitation de la source unique s'apparente a un processus d'emission sequentielle. La comparaison des donnees avec des modeles de reference, bases respectivement sur la multifragmentation et la decroissance sequentielle, tend, quant a elle, a prouver la coexistence des deux mecanismes de desexcitation.}
place = {France}
year = {1999}
month = {Jul}
}