Symmetry energy extracted from the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi mathvariant="normal">S</mml:mi><mml:mi>π</mml:mi><mml:mi>RIT</mml:mi></mml:mrow></mml:math> pion data in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>Sn</mml:mi><mml:mo>+</mml:mo><mml:mi>Sn</mml:mi></mml:mrow></mml:math> systems
Gao-Chan Yong
Abstract
With the improved particular isospin-dependent Boltzmann-Uehling-Uhlenbeck transport model including the nucleon-nucleon short-range correlations, the ratios and yields of ${\ensuremath{\pi}}^{\ensuremath{-}}$ and ${\ensuremath{\pi}}^{+}$ in $\mathrm{Sn}+\mathrm{Sn}$ systems with different asymmetries at 270 MeV/nucleon are studied. It is found that the yields of ${\ensuremath{\pi}}^{\ensuremath{-}}$ and ${\ensuremath{\pi}}^{+}$ and their ratios in $\mathrm{Sn}+\mathrm{Sn}$ systems characterized by different neutron to proton ratios obtained from very recent $\mathrm{S}\ensuremath{\pi}\mathrm{RIT}$ pion data are quite well described by the model, especially when a soft symmetry energy with $L({\ensuremath{\rho}}_{0})=66.75\ifmmode\pm\else\textpm\fi{}24.75$ MeV is used. The calculations also clearly demonstrate that the high-momentum tail of the nucleon initialization in momentum space strongly affects the yields and ratios of pion production in $\mathrm{Sn}+\mathrm{Sn}$ systems with different asymmetries near or below threshold. In addition, given many insoluble theoretical uncertainties in transport models, multisystem experimental measurements with various $N/Z$ asymmetries are proposed to extract the symmetry energy less model dependently by using heavy-ion collisions.