Photon radiation from heavy ion collisions--Early Stage

Fu-Ming LIU

（刘复明）

Thermal Photons and Dileptons ， BNL ， August 20-22

• Motivations

• Approach

• Results

• Conclusions

Outline

2

Photons carry us most information of our universe to us !To understand the puzzles of our universe, we shouldunderstand photons from heavy ion collisions first.

Our brilliant universe

3

Direct photon V2

PHENIX, Phys. Rev. Lett. 109, 122302 (2012)

Observed as large as V2 of pions!

4

Too large V2 to explain

Chatterjee et al, arXiv:1305.6443.

Puzzle ? !

pT

(GeV/c)

Direct photon v3 are observed as large as pions, too!

PHENIX: S. Mizuno QM2014

Direct photon V3

5

6

More puzzling

What’s hot, what’s not ?

Talk by Rene Bellwied At 3rd International Symposium on Non-equilibrium Dynamics Crete Greece, June 2014.

Direct Photon Sources

),(1 2

/2t

2,t

2QzD

zpdyd

dNdz

pdyd

dNcc

c

c

gqcc

)ˆˆˆ()(ˆ

ˆ),(),( 2

/2

/AB2

)LO(

utscdabtd

dsMxGMxGdxdxT

pdyd

dNbBb

abaAaba

t

AB

Jets lose energy will effect!

1. Leading Order (LO) contribution

2. Fragmentation contribution (Frag.)

3. Thermal contribution from QGP and HG

upETExd

pdyd

dN

t

**thermal

42

thermal

),,(

4. Jet-photon conversion (JPC)

),( *JPC

42

TExdpdyd

dN

t

JPC

Jet + Plasma enhance photons

Jet + Plasma reduce photons

FML, K.Werner, J.Phys.G, 36(2009)035101.

7

Constrain jet energy loss

: QGP fraction

: E-loss per unit distance in BDMPS formulism

A common

D=1.5

for various

Centralities!

D

FML, T.Hirano, K.Werner, Y. Zhu, Phys.Rev.C79,014905(2009) 8

9

Competition of sources FML, T.Hirano, K.Werner, Y. Zhu, J.Phys.G, 36 (2009) 064072.

Phys.Rev.C79 (2009) 014905.

Pt spectra are well understood with hadron date constrained hydro!

Energy loss reduces frag., but JPC makes up.

High pt photon data show almost a cancelation!

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Simplify Direct Photon Sources

1.Prompt photons

2. Thermal photons

P

P

thermal4 * *

thermal2( ) ( , ),

t

dNd x E T E p u

dyd p

Based on High pt direct photon data

Dominant at high pt , zero v2.

Dominate at low pt , u, T V2(pt)

Emission rate : QGP phase-- AMY2001 HG phase -- TRG2004Question : Photon emission Before QGP formation?

Hydro evolution ),,,,...(,,, zyxBsu

Initial condition: event generator NeXuS, EPOS

0 T

Freeze-out:

Evolution:EoS from Lattice QCD

EPOS K.Werner, et al, PRC85, 064907 (2012) PRL112, 232301(2014) PRC89.064903 (2014) …..3+1 D hydro, viscosity effects: Q.Shen’s talk

+ uRQMD for hadron production

for photon production

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Bulk Hadrons & Thermal Photons

Hydro initial time

• Hadrons are not sensitive to it!

• Photons are extremely sensitive to it!

Questions:

• How big should be ?

• How is the system before ?

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From nPDF toward QGP • Thermalization

• Chemical equilibrium – balance btw quarks and gluons

from a gluon-dominant system to a QGP Glasma, L.Mclerran

by Aleksi Kurkela, QM2014

13

My Treatment to Glasma• Thermal equilibrium

• Chemical equilibrium

Quark distribution

quark fugacity ,

better to get from transport theory.

Modeling ξ: increase from almost zero at

saturate to unity at

at midrapidity.

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Photon emission rate in non-eq. Transport theory:

Note: EoS

arXiv: 1305.5284 A matter at high T but low photon emission rate!

Photon emission rate will be suppressed by a factor of for diagrams with n-quark incoming lines:

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Is hydro evolution still valid, concerning to hadron data constraints?

Yes, because

1) QGP is formed before hadrons freeze-out : particle yields, v2/n scaling..

2) Before QGP formation, dynamical EoS e=e(P) remains approximately the same, no matter the value of quark fugacity.

The Whole Photon Emission

QGP phase-- AMY2001 HG phase -- TRG2004

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Spectrum, v2, v3, v4 ...

• In E-b-E case, vary with event, pt and PID.

However, it is easy to show

• So we can get

• Then take event average.

One for all, based on

: average over all particles in each event

thermal4 * *

thermal2( ) ( , ),

t

dNd x E T E p u

dyd p

18

Two more reasons to distinguish

1. Small limit

2. Lesson from pp at 7TeV

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Q: If is extremely small, what will happen?

A: Very hot system! Then…

300MeV500MeV700MeV900MeV

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21

Photon Spectrum

High tail from thermal photons, harder than prompt photons,

if we don’t distinguish

Small τQGP

Large

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A lesson from pp at 7TeV

Motivated by Ridge in pp,hydro evolution was constructed.

ALICE Data tells us: It’s necessary to distinguish Otherwise, overestimate photons!

FML, K.Werner,

Phys.Rev.Lett.106:242301,(2011)

Results:

(0.35fm/c) . Extract with

1. Pb+Pb 2.76TeV EPOS217v3

2. Au+Au 200GeV EPOS3102

ξ(τ,…).

FML and Sheng-Xu Liu, Phys.Rev.C 89, 034906 (2014)

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24

Pb+Pb 2.76TeV EPOS217v3

Thermal photons with different

1. Hadron FO constrains the spectrum of very low pt region.2. modifies the slope and v2 of thermal photons!

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Prompt + Thermal photons

QGP formation time has strong effects on v2. So does v3, v4, ….

26

Extract QGP formation time

are extracted from data.

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Predict high order harmonics

High order harmonics of direct photons are comparable of pions.

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Au+Au at 200GeV 0-20%

EPOS3.102

Preliminary

Right

Left

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Au+Au 200GeV 20-40%

Preliminary

A little too hot!

V3-c% dependence

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Predict high order harmonics

Preliminary

31

Au+Au at 200GeV 0-20%

Preliminary

Made by Sheng-Xu Liu

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Conclusions

• Glasma is the key to solve photon puzzles.

• Photon data carry us unique information of the early stage !

• Early stage of HIC provides us a special example,

massive but “dark”, useful for astrophysics and cosmology.

Thank you for your attention!