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Register a new userConstraining the symmetry energy with heavy-ion collisions and Bayesian analyses
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Efficiency corrected single ratios of neutron and proton spectra in central $^{112}$Sn+$^{112}$Sn and $^{124}$Sn+$^{124}$Sn collisions at 120 MeV/u are combined with double ratios to provide constraints on the density and momentum dependencies of the isovector mean-field potential. Bayesian analyses of these data reveal that the isoscalar and isovector nucleon effective masses, $m_s^* - m_v^*$ are strongly correlated. The linear correlation observed in $m_s^* - m_v^*$ yields a nearly independent constraint on the effective mass splitting $Delta m_{np}^*= (m_n^*-m_p^*)/m_N = -0.05_{-0.09}^{+0.09}delta$. The correlated constraint on the standard symmetry energy, $S_0$ and the slope, $L$ at saturation density yields the values of symmetry energy $S(rho_s)=16.8_{-1.2}^{+1.2}$ MeV at a sensitive density of $rho_s/rho_0 = 0.43_{-0.05}^{+0.05}$.
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A new version of the improved quantum molecular dynamics model has been developed to include standard Skyrme interactions. Four commonly used Skyrme parameter sets, SLy4, SkI2, SkM* and Gs are adopted in the transport model code to calculate the isospin diffusion observables as well as single and double ratios of transverse emitted nucleons. While isospin diffusion observables are sensitive to the symmetry energy term, they are not very sensitive to the nucleon effective mass splitting parameters in the interactions. Our calculations show that the high energy neutrons and protons and their ratios from reactions at different incident energies provide a robust observable to study the momentum dependence of the nucleon effective mass splitting. However the sensitivity of effective mass splitting effect on the n/p yield ratios decreases with increasing beam energy, even though high energy proton and neutron are produced more abundantly at high beam energy. Our calculations show that the optimum incident energy to study nucleon effective masses is between 100-200 MeV per nucleon.
Relativistic models can be successfully applied to the description of compact star properties in nuclear astrophysics as well as to nuclear matter and finite nuclei properties, these studies taking place at low and moderate temperatures. Nevertheless, all results are model dependent and so far it is unclear whether some of them should be discarded. Moreover, in the regime of hot hadronic matter very few calculations exist using these relativistic models, in particular when applied to particle yields in heavy ion collisions. In the present work we comment on the known constraints that can help the selection of adequate models in this regime and investigate the main differences that arise when the particle production during a Au+Au collision at RHIC is calculated with different models.
A summary of the QM19 conference is given by highlighting a few selected results. These are discussed as examples to illustrate the exciting future of heavy-ion collisions and the need for further instrumentation. (The arXiv version is significantly longer than the printed proceedings, with more figures.)
This document was prepared by the community that is active in Italy, within INFN (Istituto Nazionale di Fisica Nucleare), in the field of ultra-relativistic heavy-ion collisions. The experimental study of the phase diagram of strongly-interacting matter and of the Quark-Gluon Plasma (QGP) deconfined state will proceed, in the next 10-15 years, along two directions: the high-energy regime at RHIC and at the LHC, and the low-energy regime at FAIR, NICA, SPS and RHIC. The Italian community is strongly involved in the present and future programme of the ALICE experiment, the upgrade of which will open, in the 2020s, a new phase of high-precision characterisation of the QGP properties at the LHC. As a complement of this main activity, there is a growing interest in a possible future experiment at the SPS, which would target the search for the onset of deconfinement using dimuon measurements. On a longer timescale, the community looks with interest at the ongoing studies and discussions on a possible fixed-target programme using the LHC ion beams and on the Future Circular Collider.
The fragmentation of quasi-projectiles from the nuclear reaction $^{40}Ca$ + $^{12}C$ at 25 MeV/nucleon was used to produce excited states candidates to $alpha$-particle condensation. The experiment was performed at LNS-Catania using the CHIMERA multidetector. Accepting the emission simultaneity and equality among the $alpha$-particle kinetic energies as experimental criteria for deciding in favor of the condensate nature of an excited state, we analyze the $0_2^+$ and $2_2^+$ states of $^{12}$C and the $0_6^+$ state of $^{16}$O. A sub-class of events corresponding to the direct 3-$alpha$ decay of the Hoyle state is isolated.
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