The relativistic mean-field approach was implemented in the Lanzhou quantum molecular dynamics transport model(LQMD.RMF). Using the LQMD.RMF, the properties of collective flow and pion production were investigated sys...The relativistic mean-field approach was implemented in the Lanzhou quantum molecular dynamics transport model(LQMD.RMF). Using the LQMD.RMF, the properties of collective flow and pion production were investigated systematically for nuclear reactions with various isospin asymmetries. The directed and elliptic flows of the LQMD.RMF are able to describe the experimental data of STAR Collaboration. The directed flow difference between free neutrons and protons was associated with the stiffness of the symmetry energy, that is, a softer symmetry energy led to a larger flow difference. For various collision energies, the ratio between the π^(-) and π^(+) yields increased with a decrease in the slope parameter of the symmetry energy. When the collision energy was 270 MeV/nucleon, the single ratio of the pion transverse momentum spectra also increased with decreasing slope parameter of the symmetry energy in both nearly symmetric and neutron-rich systems.However, it is difficult to constrain the stiffness of the symmetry energy with the double ratio because of the lack of threshold energy correction on the pion production.展开更多
Taking into account the effects of shadowing and jet quenching, the large transverse momentum distribution of K＋, π＋ and K＋/π＋ ratios at s = 200 GeV originating from resolved photoproduction processes is calcula...Taking into account the effects of shadowing and jet quenching, the large transverse momentum distribution of K＋, π＋ and K＋/π＋ ratios at s = 200 GeV originating from resolved photoproduction processes is calculated based on perturbative quantum chromodynamics. It is found that the contribution of K＋ and π＋ produced by photoproduction processes is evident. The K＋ /π＋ ratios in Au-Au collisions show an obvious enhancement compared with p p collisions. The numerical results indicate that the photoproduetion processes are good modification for kaon and pion production.展开更多
The upgrade of the MAX-lab injector and the construction of MAX Ⅲ, provided the opportunity for upgrading the tagged-photon facility and thus lead to the possibility of more extensive program in nuclear physics resea...The upgrade of the MAX-lab injector and the construction of MAX Ⅲ, provided the opportunity for upgrading the tagged-photon facility and thus lead to the possibility of more extensive program in nuclear physics research. This upgrade increased the injected electron energy to an eventual maximum of 250 MeV and allows for the extraction of electrons from the MAX Ⅰ ring operated in the stretcher mode. The first stretched beam was delivered in September 2005. The tagged-photon facility was commissioned in parallel with the commissioning of new experimental equipment. The PAC approved experimental program is current in progress, including measurements of pion photoproduction below the △（1232）. The efforts at the tagged photon-facility are pursued within an international collaboration with around fifty members.展开更多
基金This study was supported by the National Natural Science Foundation ofChina(Nos.12147106,12175072,and 11722546)the Talent Programof South China University of Technology(No.20210115).
文摘The relativistic mean-field approach was implemented in the Lanzhou quantum molecular dynamics transport model(LQMD.RMF). Using the LQMD.RMF, the properties of collective flow and pion production were investigated systematically for nuclear reactions with various isospin asymmetries. The directed and elliptic flows of the LQMD.RMF are able to describe the experimental data of STAR Collaboration. The directed flow difference between free neutrons and protons was associated with the stiffness of the symmetry energy, that is, a softer symmetry energy led to a larger flow difference. For various collision energies, the ratio between the π^(-) and π^(+) yields increased with a decrease in the slope parameter of the symmetry energy. When the collision energy was 270 MeV/nucleon, the single ratio of the pion transverse momentum spectra also increased with decreasing slope parameter of the symmetry energy in both nearly symmetric and neutron-rich systems.However, it is difficult to constrain the stiffness of the symmetry energy with the double ratio because of the lack of threshold energy correction on the pion production.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11065010 and 11465021
文摘Taking into account the effects of shadowing and jet quenching, the large transverse momentum distribution of K＋, π＋ and K＋/π＋ ratios at s = 200 GeV originating from resolved photoproduction processes is calculated based on perturbative quantum chromodynamics. It is found that the contribution of K＋ and π＋ produced by photoproduction processes is evident. The K＋ /π＋ ratios in Au-Au collisions show an obvious enhancement compared with p p collisions. The numerical results indicate that the photoproduetion processes are good modification for kaon and pion production.
基金We thank the US National Science Foundation, the Swedish Research Council, and Lund University for their support of the Nuclear Physics Program at Lund.
文摘The upgrade of the MAX-lab injector and the construction of MAX Ⅲ, provided the opportunity for upgrading the tagged-photon facility and thus lead to the possibility of more extensive program in nuclear physics research. This upgrade increased the injected electron energy to an eventual maximum of 250 MeV and allows for the extraction of electrons from the MAX Ⅰ ring operated in the stretcher mode. The first stretched beam was delivered in September 2005. The tagged-photon facility was commissioned in parallel with the commissioning of new experimental equipment. The PAC approved experimental program is current in progress, including measurements of pion photoproduction below the △（1232）. The efforts at the tagged photon-facility are pursued within an international collaboration with around fifty members.
