Transcript The dynamical particle ratio fluctuation in heavy- ion collisions

Study the particle ratio fluctuations in heavyion collisions
Limin Fan (樊利敏)
Central China Normal University
(CCNU)
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Outline
 Introduction.
 Model and calculation.
 Results and discussion.
 Summary and outlook.
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Evolution of High Energy Heavy Ion Collisions
Freeze out Stage: ~10-15fm/c
Chemical freeze out: Inelastic scatt. cease.
Kinetic freeze out: Elastic scatt. cease.
QGP thermal and Expansion Stage: 1-10fm/c
Collective expansion, Parton energy loss et al.,
Hadronization: Recombination and coalescence.
Pre-equilibrium parton hard
scattering.
arxiv:0809.2482, hep-ph/0407360
initial state
hadronic phase
and freeze-out
QGP and
hydrodynamic expansion
pre-equilibrium
hadronization
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QCD Phase Diagram
At high enough energy density ordinary matter
will undergoes a transition into a plasma-like
phase.
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.
k /
p /  and k / p fluctuations could be
related to strangeness fluctuations, baryon
number fluctuations and baryon-strangeness
correlations at mid-rapidity.
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Fluctuations Measure
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PACIAE model
PACIAE is based on PYTHIA
(A) Initiation
(i) Distributing nucleons according to Woods Saxon,
(ii) participant nucleons inside OLZ
(iii)spectator nucleons outside OLZ but inside nucleus-nucleus collision
system
y
px  p y  0, pz  pbeam
p
OLZ
T
b

z
x
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(iv) Construct nucleon collision time list with NN total
cross section & straight trajectory
(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 re-scattering (parton evolution)
(i) Construct parton collision time list with parton-parton
total cross section
(ii) Perform each parton-parton collision by 2→2
pQCD differential cross section
(C) Parton hadronization with SF or CM
(D) Hadron evolution (re-scattering)
(i) Construct hadron collision time list with hh
total cross section
(ii) Perform each hh collision by differential hh
cross section
Ben-Hao Sa, Dai-Mei Zhou, et.al.,
Comput. Phys. Commun. 183(2012)333, 184(2013) 1476
Calculation
Early measurements of particle ratio fluctuations utilized the variable
dyn
Where dyn 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.
Another observable,  dyn,is also proposed to study the deviation from Poisson
behavior. the observable  dyn for particle N1, N2 can be written as
 dyn ( N1 / N 2 ) 
 N1 ( N1  1)   N 2 ( N 2  1) 
 N1 N 2 


2
 N1  2
 N2 2
 N1  N 2 
The advantage of  dynis that it does not require the creation of mixed events.
A Poisson simulation also shows that  dyn provide more stable results compare
to dyn if the statistics is limited
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Calculation
 dyn  0
Statistical fluctuation
poisson distribution
If kaons and pions distribution are Poisson2 and independent of each other
 N K ( N K  1)  N K 
One would expect
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 N ( N  1)  N 
 NKN  NK  N 
 dyn  0
The production of corresponding pairs are
highly correlated
The negative value of  dyn means the cross-correlation terms dominate,which
could be due to the proton-pion and kaon-pion correlation from resonance
decay.
 dyn  0
High fluctuation
low correlation
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Identified particle numbers
Identified particle numbers used in the  dyn 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
s NN = 11.5,19.6,39,62.4 and 200 GeV.
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Results of the charge dependent particle ratio fluctuations
The opposite sign fluctuations
 (k  /  ) and  (k  /  )
dyn
dyn
The same sign fluctuations
 (k  /  ) and  (k  /  )
dyn
Result of  (k   /   ) 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).
dyn
dyn
The opposite sign fluctuations
show more negative value due
to neutral resonance decay
K * (892)  K    
The STAR data are compared to theoretical model predictions!
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Results of the charge dependent particle ratio fluctuations
The opposite sign fluctuations
 ( p  /  )
and  ( p  /  )
dyn
dyn
The same sign fluctuations
 ( p  /  ) and  ( p  /  )
dyn
Result of  ( p   /   ) 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).
dyn
dyn
The experimental data show
that the opposite sign
fluctuations show more negative
value due to neutral resonance
decays
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Results of the charge dependent particle ratio fluctuations
k/p fluctuations are related to baryonstrangeness correlations,can be used
as a tool to study the deconfinement
phase transition.
Results of  (k   / p  ) 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).
dyn
The results of  (k   / p  )are close to zero,
at some energy the results are positive
dyn
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Results of the charge independent particle ratio fluctuations
Energy dependence of  (k /  ) ,  ( p /  ) and  (k / p) . model predication from
PACIAE (black squares), UrQMD (blue trangles) and STAR (blank trangles),
dyn
dyn
dyn
using the STAR experimental acceptance and those calculations are
compared at Au+Au centrality collision with S =11.5,19.6,39,62.4 and 200
GeV
NN
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Results of the charge independent particle ratio fluctuations
P /   ( N P   N P  ) /( N   N  )
K /   ( N K  N K ) /( N   N  )




K / P  ( N K   N K  ) /( N P   N P  )
The results calculated by the PACIAE model of  (k /  ) and  ( p /  )
are nearly the same, and are more negative than the UrQMD and
STAR results.
dyn
, ,  all decay to
dyn
p,  and K * (892), K1 (1270)  decay to K  
The result of dynamical k/p ratio fluctuation in the PACIAE model
have the same trend withSTAR and UrQMD model.
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Summary
1. All of the opposite sign fluctuations are larger than the
same sign fluctuations.
2. We see either a weak energy dependence or monotonic
decrease with decreasing energy At sNN  200GeV both sign
fluctuations are nearly the same.
3.The PACIAE model results of  (k   /   ) agree with
STAR experimental results fairly well.
dyn
4.For dynamical K /  and P /  fluctuations PACIAE model
results are negative and having larger fluctuation than
UrQMD and STAR
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Thank you !
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