Eur. Phys. J. A (2014) 50: 37
https://doi.org/10.1140/epja/i2014-14037-6

Review

Probing nuclear symmetry energy at high densities using pion, kaon, eta and photon productions in heavy-ion collisions

¹ Department of Physics, Tsinghua University, 100084, Beijing, China
² Collaborative Innovation Center of Quantum Matter, Beijing, China
³ Institute of Modern Physics, Chinese Academy of Sciences, 730000, Lanzhou, China
⁴ Department of Physics and Astronomy, Shanghai Jiao Tong University, 200240, Shanghai, China
⁵ Department of Physics and Astronomy, Texas A&M University-Commerce, 75429-3011, Texas, USA
⁶ National Institute of Metrology, 100013, Beijing, China
⁷ Institute of Particle Physics, Central China Normal University, 430079, Wuhan, China

^* e-mail: xiaozg@tsinghua.edu.cn

Received: 30 July 2013
Revised: 22 September 2013
Accepted: 27 September 2013
Published online: 26 February 2014

Abstract

The high-density behavior of nuclear symmetry energy is among the most uncertain properties of dense neutron-rich matter. Its accurate determination has significant ramifications in understanding not only the reaction dynamics of heavy-ion reactions, especially those induced by radioactive beams, but also many interesting phenomena in astrophysics, such as the explosion mechanism of supernova and the properties of neutron stars. The heavy-ion physics community has devoted much effort during the last few years to constrain the high-density symmetry using various probes. In particular, the / ratio has been most extensively studied both theoretically and experimentally. All models have consistently predicted qualitatively that the / ratio is a sensitive probe of the high-density symmetry energy especially with beam energies near the pion production threshold. However, the predicted values of the / ratio are still quite model dependent mostly because of the complexity of modeling pion production and reabsorption dynamics in heavy-ion collisions, leading to currently still controversial conclusions regarding the high-density behavior of nuclear symmetry energy from comparing various model calculations with available experimental data. As more / data become available and a deeper understanding about the pion dynamics in heavy-ion reactions is obtained, more penetrating probes, such as the K ⁺/K ⁰ ratio, meson and high-energy photons are also being investigated or planned at several facilities. Here, we review some of our recent contributions to the community effort of constraining the high-density behavior of nuclear symmetry energy in heavy-ion collisions. In addition, the status of some worldwide experiments for studying the high-density symmetry energy, including the HIRFL-CSR external target experiment (CEE) are briefly introduced.