1. PACIAE model analysis of particle ratio fluctuations in heavy-ion collisions Limin Fan ( 樊利敏 ) Central China Normal University (CCNU) 1 第十五届全国核物理大会

2. Outline  Introduction.  Model and calculation.  Results and discussion.  Summary 2

3. 3 Pre-equilibrium parton hard scattering. QGP thermal and Expansion Stage: 1-10fm/c Collective expansion, Parton energy loss et al., Hadronization: Recombination and coalescence. Freeze out Stage: ~10-15fm/c Chemical freeze out: Inelastic scatt. cease. Kinetic freeze out: Elastic scatt. cease. arxiv:0809.2482, hep-ph/0407360 Evolution of High Energy Heavy Ion Collisions initial state pre-equilibrium QGP and hydrodynamic expansion hadronization hadronic phase and freeze-out

4. QCD phase transition 4 At high enough energy density,the quark/gluon to hadron phase transition may lead to significant fluctuation. The correlation between strangeness S and baryon number B is sensitive to the state of matter created in heavy-ion collisions. In a hadron gas, kaons (S=-1,B=0) allows for strangeness number unrelated to baryon number

5. 5 PACIAE model PACIAE is based on PYTHIA (A) parton Initiation (iii) Distributing nucleons according to Woods Saxon (i) participant nucleons inside OLZ (ii) spectator nucleons outside OLZ but inside nucleus-nucleus collision system OLZ y x p T z b (iv) Construct nucleon collision time list with NN total cross section & straight trajectory

6. (v) Each NN collision performed by PYTHIA with switching-off SF & breaking diquark. (vi) Resulted initial state,consist of partons after all of the NN collision pairs are exhausted (B) Parton evolution (re-scattering) (C) Parton hadronization with SF or MC (D) Hadron evolution (re-scattering) Ben-Hao Sa, Dai-Mei Zhou, et.al., Comput. Phys. Commun. 183(2012)333, 184(2013) 1476

7. 7 Calculation The advantage of a ratio fluctuation is that the volume fluctuation cancels out. The advantage of is that it does not require the creation of mixed events. A Poisson simulation also shows that provide more stable results compare to if the statistics is limited Early measurements of particle ratio fluctuations utilized the variable Another observable,,is also proposed to study the deviation from Poisson behavior. the observable for particle can be written as Where is the relative width of the event-by-event particle-ratio ( k/π, p/π or k/p )distribution in either real or mixed events.

8. Calculation 8 Statistical fluctuation poisson distribution The production of corresponding pairs are highly correlated High fluctuation low correlation The negative value of means the cross-correlation terms dominate,which could be due to the proton-pion and kaon-pion correlation from resonance decay. If kaons and pions distribution are Poisson and independent of each other One would expect

9. Identified particle numbers 9 Identified particle numbers used in the calculation,0-5% centrality, we use the PACIAE model within the STAR experimental acceptance charged kaons and pions are selected with transeverse momentum 0.2 < pt < 1.6Gev/c and pseudorapidity |η| < 1.0 The number of participating nucleons are from Au+Au collisions at = 11.5,19.6,39,62.4 and 200 Gev.

10. Results of the charge dependent particle ratio fluctuations 10 The STAR data are compared to theoretical model predictions! The same sign fluctuations and The opposite sign fluctuations show more negative value due to neutral resonance decay Result of in 0-5% most central Au+Au collisions calculated by the PACIAE model (red stars and circles) and compared with STAR experimental results (blue triangles). The opposite sign fluctuations and

11. Results of the charge dependent particle ratio fluctuations 11 Result of in 0-5% most central Au+Au collisions calculated by the PACIAE model (red stars and circles) and compared with STAR experimental results (blue triangles). The opposite sign fluctuations and The same sign fluctuations and The opposite sign fluctuations show more negative value due To decay

12. 12 Results of the charge dependent particle ratio fluctuations k/p fluctuations are related to baryon- strangeness correlations,can be used as a tool to study the deconfinement phase transition. Results of in 0-5% most central Au+Au collisions calculated by the PACIAE model (red stars and circles) and compared with STAR experimental results (blue triangles). The results of are close to zero, at some energy the results are positive

13. 13 Results of the charge independent particle ratio fluctuations Energy dependence of, and. model predication from PACIAE (black stars), UrQMD (blue trangles) and HSD (pink trangles),using the STAR experimentai acceptance and those calculations are compared at Au+Au centrality collision with =11.5,19.6,39,62.4 and 200 Gev.

14. 14 Results of the charge independent particle ratio fluctuations Dynamical k/p ratio fluctuation in the PACIAE model have the same trend with HSD and UrQMD model. The results calculated by the PACIAE model of and are nearly the same, and are more negative than the UrQMD and HSD model. all decay to and decay to

15. Summary 15 1. All of the opposite sign fluctuations are larger than the same sign fluctuations. 2. For charge dependent particle ratio fluctuation,we see either a weak energy dependence or monotonic decrease with decreasing energy At both sign fluctuations are nearly the same. 4.For dynamical and fluctuations PACIAE model results are negative and having larger fluctuation than UrQMD and HSD 3.The PACIAE model results of agree with STAR experimental results fairly well.

16. Thank you ! 16