Study the particle ratio fluctuations in heavy-ion 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.2

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Pre-equilibrium parton hard scattering.

QGP thermal and Expansion Stage: 1-10fm/cCollective expansion, Parton energy loss et al., Hadronization: Recombination and coalescence.

Freeze out Stage: ~10-15fm/cChemical freeze out: Inelastic scatt. cease.Kinetic freeze out: Elastic scatt. cease.

arxiv:0809.2482, hep-ph/0407360

Evolution of High Energy Heavy Ion Collisions

initial state

pre-equilibrium

QGP andhydrodynamic expansion

hadronization

hadronic phaseand freeze-out

QCD Phase Diagram

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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. and fluctuations could be related to strangeness fluctuations, baryon number fluctuations and baryon-strangeness correlations at mid-rapidity.

pk //k /p

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

OLZ

y

x

p T

z

bbeamzyx pppp ,0

(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

(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

(B) Parton re-scattering (parton evolution)

(i) Construct parton collision time list with parton-parton total cross section

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Calculation

21

212

2

222

1

1121 2)1()1()/(

NNNN

NNN

NNNNNdyn

The advantage of is that it does not require the creation of mixed events.A Poisson simulation also shows that provide more stable results compare

to if the statistics is limiteddyn

dyn

dyn

dynEarly measurements of particle ratio fluctuations utilized the variable

Another observable, ,is also proposed to study the deviation from Poisson behavior. the observable for particle can be written as 21,NNdyn

dyn

dynWhere 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.

Calculation

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Statistical fluctuation poisson distribution

0dyn The production of corresponding pairs are highly correlated

0dyn High fluctuation low correlation

0dyn

The negative value of means the cross-correlation terms dominate,whichcould be due to the proton-pion and kaon-pion correlation from resonancedecay.

dyn

If kaons and pions distribution are Poisson and independent of each other One would expect

NNNN KK

2)1( KKK NNN2)1( NNN

Identified particle numbers

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Identified particle numbers used in the 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

dyn

The number of participating nucleons are from Au+Au collisions at = 11.5,19.6,39,62.4 and 200 GeV. NNs

Results of the charge dependent particle ratio fluctuations

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The STAR data are compared to theoretical model predictions!

The same sign fluctuations and )/( kdyn)/( kdyn

The opposite sign fluctuations show more negative value due to neutral resonance decay

KK )892(*

Result of 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).

)/( kdyn

The opposite sign fluctuationsand)/( kdyn

)/( kdyn

Results of the charge dependent particle ratio fluctuations

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Result of 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).

)/( pdyn

The opposite sign fluctuationsand)/( pdyn )/( pdyn

The same sign fluctuations and )/( pdyn

)/( pdyn

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 baryon-strangeness correlations,can be used as a tool to study the deconfinement phase transition.

Results of 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).

)/( pkdyn

The results of are close to zero,at some energy the results are positive

)/( pkdyn

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Results of the charge independent particle ratio fluctuations

Energy dependence of , and . model predication from PACIAE (black squares), UrQMD (blue trangles) and STAR (blank trangles),using the STAR experimental acceptance and those calculations are compared at Au+Au centrality collision with =11.5,19.6,39,62.4 and 200 GeV

)/( pkdyn)/( kdyn )/( pdyn

NNS

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Results of the charge independent particle ratio fluctuations

)/()(/

NNNNPPP

)/()(/

NNNNKKK

)/()(/ PPKKNNNNPK

The result of dynamical k/p ratio fluctuation in the PACIAE model have the same trend withSTAR and UrQMD model.

The results calculated by the PACIAE model of and are nearly the same, and are more negative than the UrQMD and STAR results.

)/( kdyn )/( pdyn

all decay to and decay to K)1270(),892( 1* KK,p ,,

Summary

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/K /P

1. All of the opposite sign fluctuations are larger than the same sign fluctuations.

GeVsNN 200 2. We see either a weak energy dependence or monotonic

decrease with decreasing energy At both sign fluctuations are nearly the same.

4.For dynamical and fluctuations PACIAE model results are negative and having larger fluctuation than UrQMD and STAR

3.The PACIAE model results of agree with STAR experimental results fairly well.

)/( kdyn

Thank you !

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