Transcript 幻灯片 1

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
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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.
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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 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
Another set of related observables have
been defined by A. Majumder et al. [2]
CSB=σSB/σ2B
CQB=σQB/σ2B
CQS=3σQS/σ2S
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
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CBS, CQS and Lattice QCD results
PRC 74, 054901 (2006)
CBS
At T=Tc both CBS and CQS jump from the
hadron gas values to 1, for an ideal
quasi-particle QGP.
( A. Majumder et al, Phys. Rev.C 74
(2006) 054901 )
CBS and CQS in hadron gas model in low
T, comparable with LQCD
calculations, are thought as potential
probes to search possible QGP
phase transition.
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AMPT (A Multi-Phase Transport) model (by Lin, Ko et al.)
default AMPT model
AMPT model with string melting
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 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.
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Conserved charges formula
The elementary sets of conserved charges
1
net upness △u, net downness △d, net strange-quarkness △s
2
baryon B , electric charge Q , strangeness S
△u =
(1)
△d =
△s =
u u
d d
ss
2

CBS  3 BS
⑶
CQS  3

2
QS
 S2
 S2
B = (△u + △d + △s)/3
(2)
Q = 2△u/3 - △d/3 - △s/3
S = -△s
2

SB
CSB 
⑷
CQB 

2
QB
CQB 
 B2
⑸
 B2
(6)
CQS 
1  CSB
2
3  C BS
2
σ2BS=<BS><B><S>
σ2S=<S2>-<S>2
Model: AMPT model
Tool: CBS, CQS
Object: Au + Au
Energy: 200GeV
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I. Rapidity dependence
No parton cascade
( 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 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.
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II. Participant number dependence
No parton cascade
In UrQMD model, the BS correlation
coefficient has no dependence on
centrality.
( Stephane Haussler et al Phys.Rev.C73(2006)021901 )
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.
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III. Different hadronic combinations
Including : Kaon, Proton, Neutron, Delta, Lambda, Sigma, Cascade, Omega
Before hadron
rescattering
w/o partonic stage
with partonic stage
Including: Lambda, Omega
After hadron
rescattering
Hadron rescattering
washes out partonic
information.
Low Ymax:
hadronic effect is
weak
high Ymax:
hadronic effect is
strong
hadronic
environment
dependence
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Ⅳ The time evolution of CBS of partonic matter
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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.
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Partonic effect on CBS for hadrons before hadron rescattering
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Hadronic effect
The killer of partonic signals:
 Comparing Melting AMPT model before ART and one after ART, ones can probably see the signals
Hadronic rescattering ?
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?
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
 depends
The similar
dependence
BS correlation
coefficient
on we
Because
the BS valuesignals
strongly
on the
hadronicof
environment,
therefore
maybe
thetonumber
of participants
after
hadron
rescattering
regardless
have
find a moderate
particle
group
to reserve
the QGP
signals. the parton cascade
process.
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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
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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
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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.
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