Baryon-strangeness correlations in a partonic/hadron transport model

1June 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


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?


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 to diagnose the nature formed at RHIC [1] .

CBS=-3σBS/σ2S

CBS can be taken as a potential tool to probethe 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=0i.e. B and S aren’t correlated

Another set of related observables havebeen defined by A. Majumder et al. [2]

CSB=σSB/σ2B

CQB=σQB/σ2B

CQS=3σQS/σ2S

[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?


CBS, CQS and Lattice QCD results

CBS

PRC 74, 054901 (2006)

At T=Tc both CBS and CQS jump from the hadron gas values to 1, for an ideal quasi-particle QGP.

CBS and CQS in hadron gas model in low T, comparable with LQCD calculations, are thought as potential probes to search possible QGPphase transition.

( A. Majumder et al, Phys. Rev.C 74(2006) 054901 )


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 resultsbefore and after ART.

So we will test BS correlation within AMPT model to explore the nature of the matter created at RHIC.


Conserved charges formula

The elementary sets of conserved charges

2

23 BSBS

S

C

2

23 QSQS

S

C

⑶

2

2SB

SBB

C

2

2QB

QBB

C

⑷

1

2SB

QB

CC

3

2BS

QS

CC

⑸

Model: AMPT model Tool: CBS, CQS

Object: Au + Au Energy: 200GeV

baryon B , electric charge Q , strangeness S

1

2

net upness u, net downness △ d, net strange-quarkness s△ △

△u = u u△d = d d△s = s s

(1)

B = ( u + d + △ △ s)/3△

Q = 2 u/3 - d/3 - s/3△ △ △

S = - s△

(2)

σ2BS=<BS>-<B><S>

σ2S=<S2>-<S>2

(6)


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 CBS increases in AMPT model with string melting scenario.

( V .Koch, Phys. Rev. Lett.95, 182301(2005) )

CBS 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


II. Participant number dependence

( Stephane Haussler et al Phys.Rev.C73(2006)021901 )

In UrQMD model, the BS correlationcoefficient 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


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


Ⅳ The time evolution of CBS of partonic matter


CBS 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, theBS correlation coefficient reduces to 0.66at |y_max|<1. It is caused due to the productions of the strange mesons.

The hadronization does not destroythe signals completely.


Partonic effect on CBS for hadrons before hadron rescattering


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 CBS?

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.


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

Default AMPT AMPT with string melting


SummaryBS 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


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.

Baryon-strangeness correlations in a partonic/hadron transport model

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