Study Of Strange And Multi-strange Particles Production And Their Nuclear Modification Factors In Nucleus-nucleus Collisions

Ultra relativistic heavy-ion collision experiment is conducted to create a high-temperature and high-density extreme environment,to explore the relevant signals of the QGP,a deconfined state of quarks and gluons,hence to study its arrtibutes and new phenomena.According to large quantities of data,it is believed that QGP can only be generated in the heavy-ions collisions,whereas,can't be generated in small systems such as p+p and p+A collisions.But recent re-search by the ALICE group has led to the surprising conclusion that QGP can also be formed in small collision systems[1].They measured the relationship between the ratio of strange hadrons to mesons with the event charged-particle multiplicity at mid-rapidity in the p+p collisions at(?)=7TeV,and found that the ratio of strange hadrons to mesons increases with the rise of the multiplicity,which is independent of the collision system and energy.Besides,the strength of strange enhancement enhances as the strangeness number increases.Just take ?(sss)for instance,the enhancement factor reaches two in high-multiplicity events.These experimental results above indicate that there is still much to do to study the generation mechanism of strange particles,which also makes it a meaningful subject for the research.Based on the PACIAE model and considering that the string can no longer be regarded as a pure dipole with the increase of energy during the process of Lund string fragmentation,?0 is used to represent the pure qq string tension,we need to reestablish the string tension in this paper to quantitatively describe the effect of gluon shrinkage and the interaction of multiple strings in a string dense environment respectively by using the string tension ?eff s and ?eff m.Taking these two effects into account at the same time,we can conclude the effective string tension ?eff s=m,which is coupled by single string and multi-string.In this paper,we research the relationship between the ratio of strange and multi-strange particles to mesons with the multiplicity or the mean number of participants<Npa,t>in p+p collisions at(?)=7TeV and Pb+Pb collisions at(?)=2.76TeV systematically under four string tension scenarios and compare experimental results respectively.In the study of p+p collisions,refering to standards in“Perugia 2011”,we can make Parj(2)=0.19 and Parj(3)=0.95,which can be used to describe the experimental results including ?particles.In the study of Pb+Pb collisions,we simulated the results under four scenarios with string tension ?0??eff s??eff m and ?eff s+m respectively when Parj(2)=0.3 and Parj(3)=0.4 firstly.It is concluded that K S 0 can be described with ?eff s perfectly;A can be described with well;? can be described with ?eff s+m perfectly,but ? can't be described with perfectly.Hence the fifth situation is introduced,that is,expanding Parj(2)and Parj(3)to 1.5 times of the original in situation,which makes Parj(2)=0.45 and Parj(3)=0.6.In this new situation,effective ten-sor is characterized by ?eff s+m(*),in which ? can be described with PACIAE.This is what other theoretical models have failed to do.Finally,we studied nuclear modification factors for strange particles and multi-strange par-ticles in Pb+Pb collisions under ?eff s+m(*)scenario at(?)=2.76TeV.The results show that the suppression effect of RAA is weakened during the process from the central collision to the pe-ripheral collision.In other words,the central collisions lose more energy than the peripheral collisions.the mass of KS0,A,? and ? increase gradually.When the transverse momentum range form 2GeV/c to 6GeV/c,PACIAE showed the suppression effect of RAA of these particles is weakened gradually,under different center degree,thus verified the existence of "dead cone"effect.