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Q. Fable

Publications and source records attributed to Q. Fable.

At least 19 recordsLinked to original sources

Measurement of the forward angle $^{12}$C+$^{12}$C fragmentation differential cross sections at 62 MeV/nucleon

The present work reports on high-precision measurements of forward-angle fragmentation differential cross sections for the [12]C +[12] C reaction at 62 MeV/nucleon using the FAZIA array. Angular distributions for fragments from Z = 1 to 6 were extracted in the range 2 <= theta_lab <= 8 degrees. Particle identification was achieved by combining the Delta E - E technique with Pulse Shape Analysis, and precise energy calibrations were performed. The results show that for heavier fragments, the angular distributions are better described by the Van Bibber formulation than by the Goldhaber model, consistent with the dominance of a wide component from dissipative processes in the measured angular range. Notably, alpha particles exhibit an anomalously narrow angular distribution, likely originating from the intrinsic cluster structure of [12]C. Comparisons with existing data at the same incident energy show very good agreement, with a more complete set of species reported here, while a kinematic scaling is proposed to compare our data with previous experimental data at 50 and 95 MeV/nucleon.

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Nuclear clustering process in heavy-ion collisions : experimental constraints on the low-temperature region of the QCD phase diagram

In this article, we study the production of Hydrogen and Helium isotopes in heavy-ion collisions in the incident energy range between 80 and 150 MeV/nucleon. We compare their inclusive multiplicities emitted in the transverse plane of the reaction with the predictions given by the thermal model. As a first step, we validate the choice of this approach to describe the experimental measurements. We also show that the transient states have to be explicitly taken into account for a good statistical description of the experimental multiplicities. From the thermodynamical parameter values obtained we complete the existing database built with the use of thermal-statistical models to reproduce particle production in the (ultra-)relativistic-energy measurements. We then proposed a new constraint on the so-called freeze-out region in the temperature (T) versus baryonic chemical potential (muB) phase diagram of the quantum chromodynamics. These new results indicate that there is a common framework to describe the hadron production and nuclear clustering processes in heavy-ion collisions.

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Model-independent measurement of isospin diffusion in Ni-Ni systems at intermediate energy

In this work we provide a model-independent experimental evaluation of the degree of isospin equilibration taking place in $^{58,64}$Ni+$^{58,64}$Ni collisions at 32 MeV/nucleon across varying reaction centralities. This result has been obtained by combining the complementary information provided by two different datasets, sharing common characteristics. The first dataset has been acquired with the INDRA setup and has been used to implement a model-independent reconstruction of the impact parameter. The second dataset has been acquired in the first experimental campaign of the coupled INDRA-FAZIA apparatus at GANIL. The neutron-to-proton content of the quasiprojectile remnant measured by FAZIA has been employed as isospin observable. The effect of isospin diffusion has been evidenced by means of the isospin transport ratio, reported as a function of the impact parameter of the collision. The evolution towards isospin equilibration from semiperipheral to more central collisions is clearly extracted. This experimental result, expanding our previous works (Phys. Rev. C 106, 024603 (2022) and Phys. Rev. C 108, 054611 (2023)), can be compared with the predictions of any transport model, and can thus be used to set constraints on the behavior of the symmetry energy term of the nuclear Equation of State at sub- to saturation densities.

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Cluster production in Xe + Sn collisions between 65-150 MeV/nucleon

Characterization of the participant-zone (PZ) in the $^{129,124}$Xe + $^{112,124}$Sn reaction at the energy range 65-150 MeV/nucleon reveals copious cluster production. A detailed study of the chemical composition as a function of the impact parameter shows that heavier clusters ($^6$He, $^{6-8}$Li, $^{7-10}$Be...) are most likely produced for central collisions. A hierarchy of the cluster production with the neutron-richness of the total system is observed, suggesting a full mixing of the projectile and target in the PZ. An estimate of the maximum density in central collisions has been deduced from the kinetic energy of the emitted fragments, reaching almost 2 time the normal density (2$\rho_0$) at 150 MeV/nucleon.

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Study of quasi-projectile properties at Fermi energies in 48Ca projectile systems

The emission of the pre-equilibrium particles during nuclear collisions at moderate beam energies is still an open question. This influences the properties of the compound nucleus but also changes the interpretation of the quasi-fission process. A systematic analysis of the data obtained by the FAZIA collaboration during a recent experiment with a neutron rich projectile is presented. The full range of charged particles detected in the experiment is within the limit of isotopic resolution of the FAZIA detector. Quasi-projectile (QP) fragments were detected in majority thanks to the forward angular acceptance of the experimental setup which was confirmed by introducing cuts based on the HIPSE event generator calculations. The main goal was to compare the experimental results with the HIPSE simulations after introducing these cuts to investigate the influence of the n-rich entrance channel on the QP fragment properties. More specifically, the lowering of N/Z of QP fragments with beam energy was found to be present since the initial phase of the reaction. Thus, pre-equilibrium emissions might be a possible candidate to explain such an effect.

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Isospin diffusion from $^{40,48}$Ca$+^{40,48}$Ca experimental data at Fermi energies: Direct comparisons with transport model calculations

This article presents an investigation of isospin equilibration in cross-bombarding $^{40,48}$Ca$+^{40,48}$Ca reactions at 35 MeV/nucleon, by comparing experimental data with filtered transport model calculations. Isospin diffusion is studied using the evolution of the isospin transport ratio with centrality. The asymmetry parameter $\delta=(N-Z)/A$ of the quasiprojectile (QP) residue is used as isospin-sensitive observable, while a recent method for impact parameter reconstruction is used for centrality sorting. A benchmark of global observables is proposed to assess the relevance of the antisymmetrized molecular dynamics (AMD) model, coupled to GEMINI++, in the study of dissipative collisions. Our results demonstrate the importance of considering cluster formation to reproduce observables used for isospin transport and centrality studies. Within the AMD model, we prove the applicability of the impact parameter reconstruction method, enabling a direct comparison to the experimental data for the investigation of isospin diffusion. For both, we evidence a tendency to isospin equilibration with an impact parameter decreasing from 9 to 3 fm, while the full equilibration is not reached. A weak sensitivity to the stiffness of the equation of state employed in the model is also observed, with a better reproduction of the experimental trend for the neutron-rich reactions.

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Quasiprojectile breakup and isospin equilibration at Fermi energies: an indication of longer projectile-target contact times?

An investigation of the quasiprojectile breakup channel in semiperipheral and peripheral collisions of $^{58,64}$Ni+$^{58,64}$Ni at 32 and 52 MeV/nucleon is presented. Data have been acquired in the first experimental campaign of the INDRA-FAZIA apparatus in GANIL. The effect of isospin diffusion between projectile and target in the two asymmetric reactions has been highlighted by means of the isospin transport ratio technique, exploiting the neutron-to-proton ratio of the quasiprojectile reconstructed from the two breakup fragments. We found evidence that, for the same reaction centrality, a higher degree of relaxation of the initial isospin imbalance is achieved in the breakup channel with respect to the more populated binary output, possibly indicating the indirect selection of specific dynamical features. We have proposed an interpretation based on different average projectile-target contact times related to the two exit channels under investigation, with a longer interaction for the breakup channel. The time information has been extracted from AMD simulations of the studied systems coupled to GEMINI++: the model calculations support the hypothesis hereby presented.

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Examination of cluster production in excited light systems at Fermi energies from new experimental data and comparison with transport model calculations

Four different reactions, $^{32}$S+$^{12}$C and $^{20}$Ne+$^{12}$C at 25 and 50 MeV/nucleon, have been measured with the FAZIA detector capable of full isotopic identification of most forward emitted reaction products. Fragment multiplicities, angular distributions and energy spectra have been measured and compared with Monte Carlo simulations, i.e. the antisymmetrized molecular dynamics (AMD) and the heavy-ion phase space exploration (HIPSE) models. These models are combined with two different afterburner codes (HF$l$ and SIMON) to describe the decay of the excited primary fragments. In the case of AMD, the effect of including the clustering and inter-clustering processes to form bound particles and fragments is discussed. A clear confirmation of the role of cluster aggregation in the reaction dynamics and particle production for these light systems, for which the importance of the clustering process increases with bombarding energy, is obtained.

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Characterization of the breakup channel in the asymmetric systems $^{40,48}$Ca+$^{12}$C at 25 and 40 MeV/nucleon

An analysis of the asymmetric reactions $^{40,48}$Ca+$^{12}$C at 25 and 40 MeV/nucleon is presented. Data have been collected with six modules of the FAZIA array. The analysis is focused on the breakup channel of sources produced in dissipative collisions, partially corresponding to incomplete fusion processes. The study has been performed both on detected fragments and on some resonances reconstructed by means of particle-fragment correlations, with a focus on the evolution of the breakup channel with the beam energy and the neutron content of the system, looking in particular at the relative velocity between the breakup fragments. Results show that also Carbon fragments reconstructed by means of particle correlations can be in large part interpreted as the light partner of a scission.

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Experimental study of the isospin transport with 40,48 Ca+ 40,48 Ca reactions at 35 MeV/nucleon

We investigate the isospin transport with 40,48 Ca+ 40,48 Ca reactions at 35 MeV/nucleon, measured with the coupling of the VAMOS high acceptance spectrometer and the INDRA charged particle multidetector. Using the quasi-projectile remnant measured with VAMOS and carefully selected light-charged-particles measured in coincidence with INDRA, a reconstruction method is applied to estimate the excited quasi-projectile (QP) on an event-by-event basis. The isospin diffusion is investigated using the isospin transport ratio with the asymmetry $\delta$ = (N -- Z)/A of the projectile as an isospin-sensitive observable and the total transverse energy of Z $\le$ 2 nuclei for experimental centrality sorting. The experimental isospin transport ratios present, for both the reconstructed QP and its remnant, a clear evolution towards isospin equilibration with increasing dissipation of the collision while the full equilibration is not reached. A smoother evolution with less discrepancies between the two mixed systems in the case of the reconstructed QP is also observed. The isospin migration is investigated using the neutron-to-proton ratio of the light-charged-clusters and the velocity of the QP remnant as a sorting parameter. More particularly, we focused on an angular region centered around the mid-rapidity of the reaction so as to characterize the low-density neck emissions. A systematic neutron-enrichment is observed and interpreted as a consequence of isospin migration, more particularly for the symmetric systems which present no isospin gradient between the projectile and the target. We also noticed that the ^{2}H and ^{4}He particles exhibit very close multiplicities independently of the sorting variable for the symmetric systems.

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First results from the INDRA-FAZIA apparatus on isospin diffusion in $^{58,64}$Ni+$^{58,64}$Ni systems at Fermi energies

An investigation of the isospin equilibration process in the reactions $^{58,64}$Ni+$^{58,64}$Ni at two bombarding energies in the Fermi regime ($32\,$MeV/nucleon and $52\,$MeV/nucleon) is presented. Data have been acquired during the first experimental campaign of the coupled INDRA-FAZIA apparatus in GANIL. Selecting from peripheral to semi-central collisions, both the neutron content of the quasiprojectile residue and that of the light ejectiles coming from the quasiprojectile evaporation have been used as probes of the dynamical process of isospin diffusion between projectile and target for the asymmetric systems. The isospin transport ratio technique has been employed. The relaxation of the initial isospin imbalance with increasing centrality has been clearly evidenced. The isospin equilibration appears stronger for the reactions at $32\,$MeV/nucleon, as expected due to the longer projectile-target interaction time than at $52\,$MeV/nucleon. Coherent indications of isospin equilibration come from the quasiprojectile residue characteristics and from particles ascribed to the quasiprojectile decay.

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Experimental study of the $^{40,48}$Ca+ $^{40,48}$Ca reactions at 35 MeV/nucleon

In this article we investigate $^{40,48}$Ca+$^{40,48}$Ca peripheral and semi-peripheral reactions at 35 MeV/nucleon. Data were obtained using the unique coupling of the VAMOS high acceptance spectrometer and the INDRA charged particle multidetector.The spectrometer allowed high resolution measurement of charge, mass and velocity of the cold projectile-like fragment (PLF), while the INDRA detector recorded coincident charged particles with nearly $4\pi$ acceptance.The measured isotopic composition of the PLF identified in VAMOS and the average light charged particle (LCP) multiplicities are promising observables to study the isospin diffusion.The detection of the PLF in coincidence with LCP allows the reconstruction of the mass, charge and excitation energy of the associated initial quasi-projectile nuclei (QP), as well as the extraction of apparent temperatures.We investigate the suitability of the isoscaling method with the PLF and the experimental reconstructed QP.The extracted $\alpha$ and $\Delta$ isoscaling parameters present a dependence on the considered system combination that could justify their use as a surrogate for isospin asymmetry in isospin transport studies.The reconstruction of the QP allows to observe an evolution of the $\alpha/\Delta$ with the size of the QP, the latter being consistent with a strong surface contribution to the symmetry energy term in finite nuclei. This leads to the conclusion that the reconstruction of the primary source is mandatory for the study of the symmetry energy term based on the isoscaling method for such reactions.

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Isospin diffusion measurement from the direct detection of a Quasi-Projectile remnant

The neutron-proton equilibration process in 48 Ca+ 40 Ca at 35 MeV/nucleon bombarding energy has been experimentally estimated by means of the isospin transport ratio. Experimental data have been collected with a subset of the FAZIA telescope array, which permitted to determine Z and N of detected fragments. For the first time, the QP evaporative channel has been compared with the QP break-up one in a homogeneous and consistent way, pointing out to a comparable n-p equilibration which suggests close interaction time between projectile and target independently of the exit channel. Moreover, in the QP evaporative channel n-p equilibration has been compared with the prediction of the Antisymmetrized Molecular Dynamics (AMD) model coupled to the GEMINI statistical model as an afterburner, showing a larger probability of proton and neutron transfers in the simulation with respect to the experimental data.

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Model independent reconstruction of impact parameter distributions for intermediate energy heavy ion collisions

We present a model-independent method to reconstruct the impact parameter distributions of experimental data for intermediate energy heavy ion collisions, adapted from a recently proposed approach for ultra-relativistic heavy ion collisions. The method takes into account the fluctuations which are inherent to the relationship between any experimental observable and the impact parameter in this energy range. We apply the method to the very large dataset on heavy ion collisions in the energy range 20-100 MeV/nucleon obtained with the INDRA multidetector since 1993, for two observables which are the most commonly used for the estimation of impact parameters in this energy range. The mean impact parameters deduced with this new method for "central" collisions selected using typical observable cuts are shown to be significantly larger than those found when fluctuations are neglected, and as expected the difference increases as bombarding energy decreases. In addition, we will show that this new approach may provide previously inaccessible experimental constraints for transport models, such as an estimation of the extrapolated mean value of experimental observables for b = 0 collisions. The ability to give more realistic, model-independent, estimations of the impact parameters associated to different experimental datasets should improve the pertinence of comparisons with transport model calculations which are essential to better constrain the equation of state of nuclear matter.

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Dynamical fission of the quasiprojectile and isospin equilibration for the system 80Kr+ 48 Ca at 35 MeV/nucleon

Experimental results concerning the dynamical fission of quasiprojectiles in semiperipheral collisions for the system 80 Kr+ 48 Ca at 35 MeV/nucleon are presented. Data have been collected with four blocks of the FAZIA setup in the first physics experiment of the FAZIA Collaboration. The degree of isospin equilibration between the two fission fragments and its dependence on their charge asymmetry is investigated. The data are compared with the results of the AMD model coupled to GEMINI as an afterburner, in order to get hints about the timescale of the process.

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Phase transition dynamics for hot nuclei

An abnormal production of events with almost equal-sized fragments was theoretically proposed as a signature of spinodal instabilities responsible for nuclear multifragmentation in the Fermi energy domain. On the other hand finite size effects are predicted to strongly reduce this abnormal production. High statistics quasifusion hot nuclei produced in central collisions between Xe and Sn isotopes at 32 and 45 AMeV incident energies have been used to definitively establish, through the experimental measurement of charge correlations, the presence of spinodal instabilities. N/Z influence was also studied.

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Study and validation of a new "3D Calorimetry" of hot nuclei with the HIPSE event generator

In nuclear thermodynamics, the determination of the excitation energy of hot nuclei is a fundamental experimental problem. Instrumental physicists have been trying to solve this problem for several years by building the most exhaustive 4Pi detector arrays and perfecting their calorimetry techniques. In a recent paper, a proposal for a new calorimetry, called "3D calorimetry", was made. It tries to optimize the separation between the particles and fragments emitted by the Quasi-Projectile and the other possible contributions. This can be achieved by determining the experimental probability for a given nucleus of a nuclear reaction to be emitted by the Quasi-Projectile. It has been developed for the INDRA data. In the present work, we wanted to dissect and validate this new method of characterization of a hot Quasi-Projectile. So we tried to understand and control it completely to determine these limits. Using the HIPSE event generator and a software simulating the functioning of INDRA, we were able to achieve this goal and provide a quantitative estimation of the quality of the QP characterization.

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A new "3D Calorimetry" of hot nuclei

In the domain of Fermi energy, it is extremely complex to isolate experimentally fragments and particles issued from the cooling of a hot nucleus produced during a heavy ion collision. This paper presents a new method to characterize more precisely hot Quasi-Projectiles. It tries to take into account as accurately as possible the distortions generated by all the other potential participants in the nuclear reaction. It is quantitatively shown that this method is a major improvement respect to classic calorimetries used with a 4$\pi$ detector array. By detailing and deconvolving the different steps of the reconstitution of the hot nucleus, this study shows also the respective role played by the experimental device and the event selection criteria on the quality of the determination of QP characteristics.

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