Baryon-strangeness correlations in a partonic/hadron transport model

1. Motivation • Results & Discussions • Summary 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

2. Net charge conservation locks? (Abhijit Majumder SQM2006) • 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.

3. Conserved quantum number (S, Q and B) correlations Event by event variable CBS ( the correlation coefficient between strangeness S and baryon number B) has been introduced by Koch et al todiagnose the nature formed at RHIC [1] . Another set of related observables have been defined by A. Majumder et al. [2] CSB=σSB/σ2B CQB=σQB/σ2B CQS=3σQS/σ2S CBS=-3σBS/σ2S CBS can be taken as a potential tool to probe the degrees of freedom and their correlations. 1) Weakly interacting quarks and gluons: CBS=1 i.e. The flavors are uncorrelated, but B and S strongly correlated. 2) A hadron gas (kaon gas): CBS=0 i.e. B and S aren’t correlated Can we use the observable sets to identify the characters of strongly interacting matter at RHIC? [1] V.Koch et al Phys Rev Lett. 95 (2005) 182301 [2] A Majumder et al Phys Rev C74(2006) 054901

4. PRC 74, 054901 (2006) CBS CBS, CQS and Lattice QCD results At T=Tc both CBS and CQS jump from the hadron gas values to 1, for an ideal quasi-particle QGP. CBS andCQS 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. We can investigate • Partonic effect: • Before ART: compare the default AMPT and string-melting AMPT. • Hadronic effect: • Compare the results • before and after ART. AMPT model with string melting default AMPT model 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. So we will test BS correlation within AMPT model to explore the nature of the matter created at RHIC.

6. net upness △u, net downness △d, net strange-quarkness △s • 1 • 2 △s = △d = △u = (1) B = (△u + △d + △s)/3 Q = 2△u/3 - △d/3 - △s/3 S = -△s σ2BS=<BS>-<B><S> σ2S=<S2>-<S>2 (6) (2) ⑸ ⑶ ⑷ Conserved charges formula The elementary sets of conserved charges Model: AMPT model Tool: CBS, CQS Object: Au + Au Energy: 200GeV

7. I. Rapidity dependence ( V .Koch, Phys. Rev. Lett.95, 182301(2005) ) 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 CBS increases in AMPT model with string melting scenario. CBS vs ηcut 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. 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 UrQMD model, the BS correlation coefficient has no dependence on centrality. II. Participant number dependence With parton cascade No parton cascade ( Stephane Haussler et al Phys.Rev.C73(2006)021901 ) 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.

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

10. ⅣThe time evolution of CBS of partonic matter

11. 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. • CBS enhancement with centrality.

12. Partonic effect on CBS for hadrons before hadron rescattering

13. The killer of partonic signals: Hadronic rescattering ? Hadronic effect • 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 CBS? 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. 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. AMPT with string melting Default AMPT The connection between BS and QS We check the connection between BS and QS by calculating BS, QS and (3-2CQS) values. It is found that the BS value extracted from the AMPT models are consist with the (3-2CQS) value perfectly  Our model results are self-consistent

15. 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: CBS ~ 1 After hadronization: CBS ~ 0.66; CBS ~ 0.3 After hadron rescattering:CBS ~ 0.2; CBS ~ 0.2 • Parton effect is important before the hadron rescattering: CBS has larger values and it increases with Ymax and Npart, while CBS is small and keeps flat w/o partonic stage. • However, hadronic rescattering washes out the partonic signal. CBS 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. 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.