Sigma Meson Production in Nuclear Reactions

The sigma meson production in p ＋ ^12C and p A- ^40Ca reactions at the incident energy Ep = 1.5 GeV is investigated within the Quantum Molecular Dynamics model. The simulation results indicate a distinctive A dependence of the sigma production, that is, the increase of A is followed by an increase of the production cross sections. We find that the σ meson production in proton-induced reactions is strongly medium-dependent, and the produced σ mesons decaying in a denser medium experience a stronger mass shift towards lower masses. This mass shift is an experimentally accessible observable in the final state pion pairs, which do not suffer from reabsorption by the surrounding nucleons. It is pointed out that the ratio of measured sigma cross sections as a function of the sigma invariant-mass from various reactions is a good probe to explore the existence of the σ meson in a dense nuclear environment.     

Differential Directed Flow of K+ Meson within Covariant Kaon Dynamics

The collective flow of positive charged kaons in heavy ion reactions at SIS energy is investigated within the frame of covariant kann dynamics. The theoretical results calculated by using quantum molecular dynamics show that the rapidity distribution of K^＋ mesons is more sensitive to the nuclear equation of state than the differential directed flow. The contribution of various K^＋ production reaction channels to the rapidity distribution of the K^＋ is also analysed in detail. The results indicate that the rapidity distribution of K^＋ mesons is mainly from the contribution of the N-△ and N-N channel. This means that the delta resonance state plays a predominantly important role for the K^＋ subthreshold production.     

Influence of Chiral Mean Field on Kaon In-plane Flow in Heavy Ion Collisions

The influence of the chiral mean field on the K⁺ in-plane flow in heavy ion collisions at SIS energy is investigated within covariant kaon dynamics. For the kaon mesons inside the nuclear medium a quasi-particle picture including scalar and vector fields is adopted and compared to the standard treatment with a static potential. It is confirmed that a Lorentz force from spatial component of the vector field provides an important contribution to the in-medium kaon dynamics and strongly counterbalances the influence of the vector potential on the K⁺ in-plane flow. The calculated results show that the new FOPI data can be reasonably described using the Brown & Rho parametrization, which partly takes into account the correction of higher order contributions in the chiral expansion. This indicates that one can abstract the information on the kaon potential in a nuclear medium from the analysis of the K⁺ in-plane flow.     

Net-Proton Nonstatistical Moments in High-Energy pp Collisions in PACIAE Model

The parton and hadron cascade model, PACIAE 2.0, is employed to calculate the net-proton nonstatistical moments in pp collisions at RHIC and LHC energies. By analyzing the results in the full phase space, it is found that the nonstatistical moments and moments products are significantly dependent on the collision energy. It is suggested that the net-proton nonstatistical moments in pp collisions may be studied in partial phase spaces with the PACIAE model.     

Comparative study of the forward and backward methods for calculating jet properties in pp collisions at s~(1/2)=7 TeV

We propose a forward method based on PYTHIA6.4 to study the jet properties in ultra-relativistic pp collisions.In the forward method,the partonic initial states are first generated with PYTHIA6.4 and then hadronized in the Lund string fragmentation model,and finally the hadronic jets are constructed from the created hadrons.Jet properties calculated with the forward method for pp collisions at √s=7 TeV are comparable to those calculated with the usual anti-kt algorithm(backward method)in PYTHIA6.4.The comparison between the backward and forward methods may contribute to the understanding of the partonic origin of jets in the backward method.     

Transverse momentum dependence of differential directed flow of Λ hyperon within kaon covariant dynamics

The transverse momentum distributions of Λ's and proton's directed flows are investigated by using Quantum Molecular Dynamics model (QMD) within the framework of covariant kaon dynamics. The calculated results show that the transverse momentum distribution of differential directed flow of Lambda hyperons is dependent appreciably on the nuclear matter equation of states (EOS). The differential directed flow of Lambda hyperons calculated with soft EOS is consistent with the experimental data,whereas the discr...