Influence of neutron-skin thickness on the π−/π+ ratio in Pb + Pb collisions

Abstract

Within an isospin-and momentum-dependent transport model (IBUU11) using as an input nucleon density profiles from Hartree-Fock calculations based on a modified Skyrme-like (MSL) model, we study the influence of the uncertainty of the neutron skin thickness on the π − /π + ratio in both central and peripheral Pb + Pb collisions at beam energies of 400 MeV/nucleon and 1000 MeV/nucleon. Within the current experimental uncertainty range of neutron skin in 208 Pb, while the neutron skin effect on the π − /π + ratio is negligible in central reactions at both energies, it increases gradually with increasing impact parameter and becomes comparable with or even larger than the symmetry energy effect in peripheral collisions especially at 400 MeV/nucleon. Moreover, we find that while the π − /π + ratio is larger with a softer E sym (ρ) in central collisions, above certain impact parameters depending on the size of the neutron skin, a stiffer E sym (ρ) can lead to a larger π − /π + ratio as most of the pions are produced at densities below the saturation density in these peripheral reactions. Therefore, a clear impact parameter selection is important to extract reliable information about the E sym (ρ) at suprasaturation densities (size of neutron skin) from the π − /π + ratio in central (peripheral) heavy-ion collisions.

Effects of energy conservation on equilibrium properties of hot asymmetric nuclear matter

“…Therefore, more in-depth studies and careful modeling of pion production in heavy ion collision are important, especially because more systematic experimental measurements of the pion yield from intermediate energy heavy ion collisions are being carried out by the FRIB-RIKEN Spirit Collaboration in Japan [9]. A lot of efforts have already been made recently to study various effects on pion production in heavy ion collisions at near-threshold energies, e.g., the pion in-medium potentials [10][11][12][13], isovector potential of ∆ [14], threshold effects [15,16], neutron-skin thickness [17], and nucleon short-range correlation [18].…”

Effect of neutron skin thickness on projectile fragmentation

“…Moreover, in this work, different neutron skin thicknesses mainly influence the neutron density distribution in the surface region of nuclei, so our study is focused on the peripheral collisions. In the peripheral collisions, the effect of neutron skin is larger than the effect due to the symmetry energy [32].…”

“…Therefore, it is interesting to study the effects of neutron skin and symmetry energy separately. The correlations between symmetry energy and the particle or fragment productions have also been investigated in many theoretical studies [32][33][34]. The flexibility of adjusting independently the size of neutron skin of colliding nuclei is useful for our analyses in this work.…”

“…Many theoretical studies show a strong correlation between symmetry energy and neutron skin size, while there is still large uncertainty of neutron skin size and symmetry energy [30,31]. As discussed in the reference [32], both the symmetry and neutron skin have effects on the particle productions. Therefore, it is interesting to study the effects of neutron skin and symmetry energy separately.…”

Symmetry potential of theΔ(1232)resonance and its effects on theπ−/π+ratio in heavy-ion collisions near the pion-prod

“…Unfortunately, several model analyses [13][14][15][16][17][18] of some existing data have so far been inconclusive. Realizing the importance of thoroughly understanding all aspects of the π − N − ∆ dynamics in isospin-asymmetric matter especially since several experiments measuring the π − /π + ratio are cur- * Email: Bao-An.Li@Tamuc.edu rently underway at RIKEN [19] and NIRS [20] besides those planned at other facilities [21,22], significant efforts have been made recently in studying effects of the in-medium pion production threshold [23], pion meanfield [24][25][26][27], electromagnetic field [28], neutron-skin [29] and nucleon-nucleon short-range correlation [30,31] on pion production mostly at intermediate energies above the pion production threshold of about 300 MeV/A. Extending these efforts, we report here results of a study on effects of the completely unknown symmetry (isovector) potential of the ∆(1232) resonance on both the total and differential π − /π + ratios in heavy-ion collisions at beam energies from 100 to 1000 MeV/A within an isospin-dependent transport model IBUU [12].…”