1. 1 June 24-29, 2007 @ Levoca, Slovakia Baryon-strangeness correlations in a partonic/hadron transport model F. Jin, Y. G. Ma, X. Z. Cai, G. L. Ma, H. Huang, J. Zuo et al. Shanghai Institute of Applied Physics, Chinese Academy of Sciences Motivation Results & Discussions Summary

2. 2 June 24-29, 2007 @ Levoca, Slovakia  For a given rapidity bin, the net conserved charges set in a deconfined phase may be maintained through the hadronic phase up to freeze-out.  The fluctuations of conserved charges within a given rapidity bin are controlled by the degrees of freedom at the temperatures achieved.  The fluctuations are divided into partonic fluctuation and hadronic fluctuation.  We need to know partonic fluctuations, but it may be contaminated by hadronic fluctuations. (Abhijit Majumder SQM2006) Net charge conservation locks?

3. 3 June 24-29, 2007 @ Levoca, Slovakia Conserved quantum number (S, Q and B) correlations Event by event variable C BS ( the correlation coefficient between strangeness S and baryon number B) has been introduced by Koch et al to diagnose the nature formed at RHIC [1]. C BS =-3σ BS /σ 2 S C BS can be taken as a potential tool to probe the degrees of freedom and their correlations. 1) Weakly interacting quarks and gluons: C BS =1 i.e. The flavors are uncorrelated, but B and S strongly correlated. 2) A hadron gas (kaon gas): C BS =0 i.e. B and S aren’t correlated Another set of related observables have been defined by A. Majumder et al. [2] C SB =σ SB /σ 2 B C QB =σ QB /σ 2 B C QS =3σ QS /σ 2 S [1] V.Koch et al Phys Rev Lett. 95 (2005) 182301 [2] A Majumder et al Phys Rev C74(2006) 054901 Can we use the observable sets to identify the characters of strongly interacting matter at RHIC?

4. 4 June 24-29, 2007 @ Levoca, Slovakia C BS, C QS and Lattice QCD results C BS PRC 74, 054901 (2006) At T=T c both C BS and C QS jump from the hadron gas values to 1, for an ideal quasi-particle QGP. C BS and C QS in hadron gas model in low T, comparable with LQCD calculations, are thought as potential probes to search possible QGP phase transition. ( A. Majumder et al, Phys. Rev.C 74 (2006) 054901 )

5. 5 June 24-29, 2007 @ Levoca, Slovakia default AMPT model AMPT model with string melting AMPT (A Multi-Phase Transport) model (by Lin, Ko et al.) AMPT is a successful model at RHIC: e.g. Elliptical flow + HBT + Mach-cone ….(Ko et al. PRC 72, 064901 (2005); PRC (2002) 034904 ;PRL 89 (2002) 152301 ; Ma et al., PLB 647 (2007) 122; PLB 641 (2006) 362. We can investigate  Partonic effect: Before ART: compare the default AMPT and string-melting AMPT.  Hadronic effect: Compare the results before and after ART. So we will test BS correlation within AMPT model to explore the nature of the matter created at RHIC.

6. 6 June 24-29, 2007 @ Levoca, Slovakia Conserved charges formula The elementary sets of conserved charges ⑶ ⑷ ⑸ Model: AMPT model Tool: C BS, C QS Object: Au + Au Energy: 200GeV 1 2 net upness △ u, net downness △ d, net strange-quarkness △ s △u = △d = △s = (1) B = ( △ u + △ d + △ s)/3 Q = 2 △ u/3 - △ d/3 - △ s/3 S = - △ s (2) σ 2 BS = - σ 2 S = - 2 (6)

7. 7 June 24-29, 2007 @ Levoca, Slovakia I. Rapidity dependence BS correlation coefficient in HIJING falls down with an increase of the maximum rapidity accepted. The trend in default AMPT model is alike to that in HIJING, but the C BS increases in AMPT model with string melting scenario. ( V.Koch, Phys. Rev. Lett.95, 182301(2005) ) C BS vs η cut is a good probe to identify partonic and hadronic effects, even within a narrow rapidity acceptance (|y|<1), in the Au+Au central collisions. With parton cascade No parton cascade

8. 8 June 24-29, 2007 @ Levoca, Slovakia II. Participant number dependence ( Stephane Haussler et al Phys.Rev.C73(2006)021901 ) In UrQMD model, the BS correlation coefficient has no dependence on centrality. The trend in Default AMPT model is alike to that in UrQMD, but in the string melting AMPT model the value increases with the increase of number of participants. In a certain middle rapidity range (|y|<0.5), if the system experiences the partonic phase, the BS correlation increases with the number of participants, i.e. stronger parton cascade effect leads to stronger BS correlation. No parton cascade With parton cascade

9. 9 June 24-29, 2007 @ Levoca, Slovakia III. Different hadronic combinations Including: Lambda, Omega Including : Kaon, Proton, Neutron, Delta, Lambda, Sigma, Cascade, Omega Before hadron rescattering After hadron rescattering Hadron rescattering washes out partonic information. Low Ymax: hadronic effect is weak high Ymax: hadronic effect is strong hadronic environment dependence w/o partonic stage with partonic stage

10. 10 June 24-29, 2007 @ Levoca, Slovakia Ⅳ The time evolution of C BS of partonic matter

11. 11 June 24-29, 2007 @ Levoca, Slovakia  C BS enhancement with centrality.  BS correlation coefficient is unity in a partonic phase consisted of quarks and gluons, because the strangeness carriers are only s and sbar quark.  When the hadronization begins, the BS correlation coefficient reduces to 0.66 at |y_max|<1. It is caused due to the productions of the strange mesons.  The hadronization does not destroy the signals completely.

12. 12 June 24-29, 2007 @ Levoca, Slovakia Partonic effect on C BS for hadrons before hadron rescattering

13. 13 June 24-29, 2007 @ Levoca, Slovakia From the dependence of BS correlation coefficient on the pseudo-rapidity before and after hadron rescattering (ART), we can see the hadronic rescattering almost destroy the qusi-partonic signals  The similar dependence of BS correlation coefficient on the number of participants after hadron rescattering regardless the parton cascade process. The killer of partonic signals: Hadronic rescattering ?  Comparing Melting AMPT model before ART and one after ART, ones can probably see the signals of partonic phase.  Unfortunately, the signals have been faded out after ART process,.  Hadronic rescattering process may be the cause that we are unable to see the QGP signals from C BS ? Hadronic effect Because the BS value strongly depends on the hadronic environment, therefore maybe we have to find a moderate particle group to reserve the QGP signals.

14. 14 June 24-29, 2007 @ Levoca, Slovakia The connection between BS and QS We check the connection between BS and QS by calculating BS, QS and (3-2C QS ) values. It is found that the BS value extracted from the AMPT models are consist with the (3-2C QS ) value perfectly  Our model results are self-consistent Default AMPT AMPT with string melting

15. 15 June 24-29, 2007 @ Levoca, Slovakia Summary  BS correlation for Au+Au @ 200 GeV/c has been investigated in the AMPT model, in 0-5% centrality: with Partonic stage: w/o partonic stage: In the initial partonic phase: C BS ~ 1 After hadronization: C BS ~ 0.66; C BS ~ 0.3 After hadron rescattering: C BS ~ 0.2; C BS ~ 0.2  Parton effect is important before the hadron rescattering: C BS has larger values and it increases with Ymax and Npart, while C BS is small and keeps flat w/o partonic stage.  However, hadronic rescattering washes out the partonic signal. C BS is close to each other between the case Melting AMPT and Default AMPT; The rapidity and centrality dependences are also similar.  To trace the partonic signals, one should find an observable which can maximum reduce the hadronic effect. So a moderate particle group as a subset to analyze BS Correlation may be a solution. The work is in progress. Thanks

16. 16 June 24-29, 2007 @ Levoca, Slovakia Which is better: BS correlation or QS correlation? Comparing the BS correlation and QS correlation, we can see the clear signals from partonic effect for BS correlation coefficient rather than QS correlation.