Effective(kinetic freeze-out) temperature, transverse flow velocity, and kinetic freeze-out volume in high energy collisions

The transverse momentum spectra of different types of particles produced in central and peripheral gold–gold(Au–Au)and inelastic proton–proton(pp)collisions at the Relativistic Heavy Ion Collider,as well as in central and peripheral lead-lead(Pb–Pb)and pp collisions at the Large Hadron Collider,are analyzed by the multi-component standard(Boltzmann–Gibbs,Fermi–Dirac,and Bose–Einstein)distributions.The obtained results from the standard distribution give an approximate agreement with the measured experimental data by the STAR,PHENIX,and ALICE Collaborations.The behavior of the effective(kinetic freeze-out)temperature,transverse flow velocity,and kinetic freeze-out volume for particles with different masses is obtained,which observes the early kinetic freezeout of heavier particles as compared to the lighter particles.The parameters of emissions of different particles are observed to be different,which reveals a direct signature of the mass-dependent differential kinetic freeze-out.It is also observed that the peripheral nucleus–nucleus(AA)and pp collisions at the same center-of-mass energy per nucleon pair are in good agreement in terms of the extracted parameters.

Transverse momentum spectra in high-energy nucleus-nucleus, proton-nucleus and proton-proton collisions

The transverse momentum distributions of final-state particles produced in nucleus-nucleus （AA）, proton-nucleus （pA）, and proton-proton （pp） collisions at high energies are investigated using a multisource ideal gas model. Our calculated results show that the contribution of hard emission can be neglected in the study of transverse momentum spectra of charged pions and kaons produced in Cu-Cu collisions at √SNN=22.5 GeV. And if we consider the contribution of hard emission, the transverse momentum spectra of p and ^-p produced in Cu-Cu collisions at √SNN=22.5 GeV, K^0 produced in Pb-Pb collisions at 158 A GeV, J/φ particles produced in p-Pb collisions at 400 GeV and π^＋, K^＋, p produced in proton-proton collisions at √s=200 GeV, can be described by the model, especially in the tail part of spectra.

RHIC能量下的^(197)Au+^(197)Au碰撞中的横向集体扩张运动

讨论了RHIC能量下核-核碰撞中的横向集体扩张运动问题.利用高能核碰撞的模型——"相对论量子分子动力学(RQMD)"产生相应的数据予以分析,并与200GeV的197Au+197Au碰撞中的横动量分布的实验数据进行比较,我们看到,高能核碰撞中的横向扩张起源于碰撞的初始阶段,但是却主要是在碰撞的后期完成.而一些多重奇异粒子,如Λ、Ξ、Ω,由于它们较早的离开碰撞系统,因而带有碰撞的早期信息.

Event patterns from negative pion spectra in proton-proton and nucleus-nucleus collisions at SPS

Rapidity-dependent transverse momentum spectra of negatively charged pions measured at different rapidities in proton-proton collisions at the Super Proton Synchrotron （SPS） at various energies within its Beam Energy Scan （BES） program are investigated by using one- and two-component standard distributions where the chemical potential and spin property of particles are implemented. The rapidity spectra are described by a double- Gaussian distribution. At the stage of kinetic freeze-out, the event patterns are structured by the scatter plots in the three-dimensional subspaces of velocity, momentum and rapidity. The results of the studies of the rapidityindependent transverse mass spectra measured at mid-rapidity in proton-proton collisions are compared with those based on the similar transverse mass spectra measured in the most central beryllium-beryllium, argon-scandium and lead-lead collisions from the SPS at its BES energies.

Universal scaling of kinetic freeze-out parameters across different collision systems at LHC energies

In this study,we perform Tsallis Blast-Wave analysis on the transverse momentum spectra of identified hadrons produced in a wide range of collision systems at the Large Hadron Collider(LHC) including pp,pPb,XeXe,and PbPb collisions.The kinetic freeze-out properties varying with event multiplicity are investigated across these systems.We find that the extracted kinetic freeze-out temperature,radial flow velocity,and non-extensive parameter exhibit a universal scaling behavior for these systems with very different geometric sizes,especially when the independent baryon Tsallis non-extensive parameter is considered.This universality may indicate the existence of a unified partonic evolution stage in different collision systems at the LHC energies.

重离子碰撞中K介子和π介子产生的统一动力学模拟

用ＲＶＵＵ模型统一地研究了重离子碰撞中产生的Ｋ介子和π介子的动力学过程．考虑了Ｋ产生和输运过程的介质效应，同时，计入了π在核物质中的传播．用它模拟了每核子１ＧｅＶ入射能量的重离子碰撞中π产生和阈下Ｋ产生过程．讨论了核介质效应对π末态性质的影响，以及对Ｋ末态性质的联带影响．计算结果表明，吸引的π光学势，影响了末态π动量分布，使横动量分布中具有小动量的π产额增大，同时明显增大了Ｋ的产额，改变了Ｋ的动量分布．这说明要合理地评价重离子碰撞的探测信息，需要统一地研究Ｋ和π的这些末态动力学作用．