photon radiation from heavy ion collisions --early stage fu-ming liu (刘复明) thermal photons...
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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
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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!
10
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
11
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 ?
12
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
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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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Photon Spectrum
High tail from thermal photons, harder than prompt photons,
if we don’t distinguish
Small τQGP
Large
22
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!
25
Prompt + Thermal photons
QGP formation time has strong effects on v2. So does v3, v4, ….
26
Extract QGP formation time
are extracted from data.
27
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
30
Predict high order harmonics
Preliminary
31
Au+Au at 200GeV 0-20%
Preliminary
Made by Sheng-Xu Liu
32
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!
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