Modeling Pion Production in Heavy-ion Collisions at Intermediate Energies

The mechanism concerning to pion production in heavy-ion collisions at intermediate energies has increasing interests recently.We modeled pion production in nucleus-nucleus collisions at intermediate energies in the framework of the Isospin-dependent Boltzmann-Uehling-Uhlenbeck(IBUU)transport model.The effects of nucleon-nucleon short-range correlations in initialization and mean-field potential,isospin-dependent in-medium baryon-baryon elastic and inelastic cross sections and pion in-medium effect are all considered in this model.It is found that the ratio and yields of π- and π+in Au+Au reaction at 400 MeV/u reproduce the FOPI/GSI data very well especially with a soft symmetry energy in the present transport model.Predictions on the single and double π-/π+ratio are made for the isotope reaction systems ^(132)Sn+^(124)Sn and ^(108)Sn+^(112)Sn at 300 MeV/u since related experiments are being carried out at RIKEN/Japan[1].

1-6 Effects of π and Δ Potential on the π-/π+ Ratio in Heavy-ion Collisions at Intermediate Energies

In recent years, it is found that π?/π+ ratio is sensitive to the high density behavior of nuclear symmetry energy. However, different transport models show that the sensitivity of the π?/π+ ratio to the symmetry energy is quite different. The discrepancies observed among the results from different models are probably due to the different symmetry potentials in these models, such as momentum-dependent or momentum-independent nucleon symmetry potentials. The momentum-dependent nucleon symmetry potential may increase the sensitivity of the neutron to proton ratio to the symmetry energy. Since the π and Δ potentials are still uncertain, in this work, we show the effects of the π and Δ potentials on the π?/π+ ratio in heavy-ion collisions at intermediate energies.

1-5 Decomposition of the Sensitivity of the Symmetry Energy Observables

To study the nuclear symmetry energy at supra-saturation densities, one generally considers that the observables probe the symmetry energy in the density region of maximal compression. Since the compression of nucleus-nucleus collision is a dynamical process, this point of view is not fully correct due to the effect of the symmetry energy at low densities. To answer which density region that some frequently used symmetry-energy-sensitive observables such as free n/p ratio or π?/π+ ratio probe, we made a study of decomposition of the sensitivity of these symmetryenergy- sensitive observables.

1-6 A Qualitative Probe to Nuclear Symmetry Energy at Supradensities

The symmetry energy, which governs many physical phenomena from the structure of exotic nuclei to astrophysicalprocesses, has many ramifications in both nuclear physics and astrophysics. Although nuclear symmetry energyand its slope at the normal density of nuclear matter have been roughly pinned down, recent interpretations ofFOPI and FOPI-LAND data by different transport models lead to divergent conclusions on the density-dependentsymmetry energy at supradensities.

1-5 Probing Nuclear Symmetry Energy by .=+ Ratio below the Pion Production Threshold

π-/π+ ratio was found to be a sensitive probe to the high-density behavior of the symmetry energy by usingseveral transport models. However, as shown in Fig. 1, at beam energies below the pion production threshold, theeffects of in-medium nucleon-nucleon scattering cross section (which is still controversial) strongly affect the valueof π??/π+ ratio[1]. It is thus necessary to do a comparative study of the effects of the in-medium NN cross sectionand the effects of the symmetry energy on pion production in heavy-ion collisions at lower beam energies.

Nuclear Bubble Configuration Probed by Proton Triggered Reaction

The nucleon spatial density distribution is of critical importance for atomic nucleus structure.The nuclei with central density depletions,usually called bubble nuclei,has been studied for more than 70 years.Based on the isospin-dependent Boltzmann-Uehling-Uhlenbeck transport model.

Probing the Curvature of Nuclear Symmetry Energy by Squeezed-out Nucleon Emission

The study of the equation of state(EoS)of nuclear matter is one of the hot topics in nuclear community.Nowadays the EoS of neutron-rich matter,especially the high-density symmetry energy,is still very controversial.The density-dependent symmetry energy around saturation can be Taylor expanded in terms of a few bulk parameters,such as the slope L.

Blind Spots of Probing the High-density Symmetry Energy in Heavy-ion Collisions

The nuclear symmetry energy,especially at suprasaturation densities,plays crucial roles in many astrophysical studies.However,nowadays the high-density behavior of the symmetry energy is still very controversial in nuclear community.To constrain the high-density behavior of the symmetry energy,neutron-rich nuclei collisions at medium energies are considered to be one of the most effective methods.While probing the high-density symmetry energy by using heavy-ion collisions,blind spots may exist.In the framework of the Isospin-dependent Boltzmann-Uehling-Uhlenbeck(IBUU)transport model,the blind spots of probing the high-density symmetry energy by the n/p ratio in the central Au+Au reaction at 300 MeV/u are demonstrated.

Interplay of Short-range Correlations and Nuclear Symmetry Energy in Hard Photon Productions from Heavy-ion Reactions at Fermi Energies

Within an isospin-and momentum-dependent transport model for nuclear reactions at intermediate energies,we investigate the interplay of the nucleon-nucleon short-range correlations(SRC)and nuclear symmetry energy Esym(ρ)on hard photon spectra in collisions of several Ca isotopes on ^(112)Sn and ^(124)Sn targets at a beam energy of 45 MeV/u.It is found that over the whole spectra of hard photons studied,the effects of the SRC overwhelm those due to the Esym(ρ).The energetic photons come mostly from the high-momentum tails(HMT)of single-nucleon momentum distributions in the target and projectile.Since the underlying physics of SRC and Esym(ρ)are closely correlated,a better understanding of the SRC will in turn help to constrain the nuclear symmetry energy more precisely in a broad density range[1].