1 surface (表层) versus volume (深层) emission in photon-hadron correlations han-zhong...
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1
Surface (表层) versus volume (深层) emission
in photon-hadron correlations
Han-Zhong Zhang
Institute of Particle Physics, Huazhong Normal University, China
Collaborators: E. Wang, J. Owens and X.-N. Wang
The international workshop for QCD/HIC July 10-12 , 2008
I. IntroductionII. Analysis on photon-hadron correlationsIII. Conclusion
2
I. Introduction
Jet quenching:
The hard jet loses a significant amount of its energy
via radiating gluon induced by multiple scattering.
hadrons
q
q
hadrons
leadingparticle
leading particle
N-N collision
hadrons
q
q
hadrons
Leading particle suppressed
leading particle suppressed
A-A collision
X.-N.Wang and M.Gyulassy, Phys.Rev.Lett.68,1480(1992)
What happens for a jet propagating inside QGP?
3
Three kinds of hard probes of QGP
1) Single jet Single hadron spectra
2) Dijet Hadron-triggered away-side hadron spectra
3) Gamma-jet Photon-triggered away-side hadron spectra
Single jet Dijet Gamma-jet
?H.Z. Zhang, J.F. Owens, E. Wang and X.-N. Wang , PRL 98(2007)212301
4
Gamma-jets were suggested for studying jet energy loss in dense matter. X. -N. Wang, Z. Huang,
and I. Sarcevic, PRL 77(1996) 231-234.
• The NLO study of the photon-triggered away-side hadron spectra will help to obtain the detailed picture of jet quenching in the whole $z_T$ region.
• The sensitivity of Gamma-jets to probe the dense matter.
)(
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Tpp
TAATAAT
hTT
TAAT
hhTT
hAAThT
T
hAA
AATAA
zD
zDzIppzwhere
dydpddydp
ddydydpdpdpddydydp
dz
dN
NzD
Motivation
5
Gamma-jet by NLO pQCD parton model
LO: NLO corrections: (e.g. 23)
FFsdPDFsTd ABAA
GamT
JetT pp
GamTp
JetTp
GamT
JetT
GamT
JetT
GamT
JetT
pp
pp
pp
,
,GamTp
1JetTp
2JetTp
),( 21 JetT
JetT
JetT ppofOnep
therefore leading to hadrons with transverse
momentum larger than that of the photons
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The fragmentation of the jets off the dense matter
The jet energy loss in a 1D expanding system:
),,(0
000
0
1
nrbd
dL
dEE g
L
dc
)/5.7/()6.1/( 02.1
001
EEdL
dE
d
Energy loss parameter
(a parameterization form of theory calculations) Enke Wang , X. -N. Wang , PRL87(2001)142301)
(X. -N. Wang , PRC70(2004)031901)
r
),()],(/),()[1(),,( 20/
/2'0/
'2'0
/
'/2
/ cch
Lggh
c
gcch
c
cLccch zDezD
z
zLzD
z
zeEzD
,//),/( ''cTgcTcTc EpLzEppz
medium vacuum
0000
/1),,,(0
0
nrb
dLg
L
7
II. High p_T photon-triggered away-side hadron spectra within a NLO pQCD parton model in heavy ion collisions
High p_T photon sources in p+p:
1) Direct photon from hard scattering
Annihilation Compton 23 one-loop
LO NLO
J. F. Owens, Rev. Mod. Phys. 59, 465(1987);H. Baer, J. Ohnemus, and J. F. Owens, Phys. Rev. D. 42, 61(1990)
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2) Fragmentation (bremsstrahlung) contributions(accompanied by nearly collinear hadrons on the same side)
J. F. Owens, Rev. Mod. Phys. 59, 465(1987);H. Baer, J. Ohnemus, and J. F. Owens, Phys. Rev. D. 42, 61(1990)
Most accompanying hadrons arewithin a cone of half-angle coneR
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isolation cuts (IC):
Isolated photons in p+p at RHIC
Because of IC selected at
RHIC, most fragmentation
contributions from parton
jets are taken out.
1.0/.,5.0 TT
cone pEradR
The left are mainly from
annihilation and Compton
processes, direct photon.
PRL 98 (2007) 012002
10
If we only consider the events where the photon has no nearly collinear hadrons accompanying on the same side, high p_T photon/photon-hadron will be dominated by annihilation and Compton processes.
Only consider on annihilation and Compton photons !!!
Focus on isolated photons now
No consideration for energy loss of jets fragmentated into photons in AA.
The left direct photons don’t encounter energy loss. Quenching picture is simply and clearly exhibited by
the correlated parton jets.
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Turbide, Gale, Jeon, Moore, Phys. Rev. C. 72 (2005) 014906
High p_T direct photon dominatesin central Au+Au at RHIC
Annihilation and Compton processes dominate for high p_T photons in AA.
12
Per-trigger yield for photon-hadron production in p+p
Data from “Matthew Nguyen for PHENIX, talk at QM2008”
dydp
dNdy
dydpdydp
dNdydpdy
T
pp
hhTT
hpp
hhT
Per-trigger yield as a
function of the p_T of
the triggered photon:
NLO pQCD results describe
the behavior of the data for
photon-hadron produced in
p+p at 200GeV
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Qualitatively, Iaa in small z_Tregion is slightly more sensitiveto epsilon_0 than Iaa in large z_Tregion.
LO
Per-trigger yield for photon-hadron in central Au+Au
NLO
Why?
)(
)()(./
/
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1)(
Tpp
TAATAAT
hTT
TAAT
hhTT
hAAThT
T
hAA
AATAA
zD
zDzIppzwhere
dydpddydp
ddydydpdpdpddydydp
dz
dN
NzD
14
T
hTT ppz
NLO Nh > 0 at z_T>1: surface emissionvacuumch
Lmediumch
LAAch DeDeD /
//
// )1(
At large z_T:medium contributions vanishdue to jet quenching, dominated by vacuum contributions.
9.0Tz
0
For LO, the jet’s energy can’t exceed the gamma’s energy, no contributions for z_T>1 region.
For NLO, because of contributions from 2->3 processes, the jet’s energy can exceed the gamma’s energy, have z_T>1 contributions.
15
T
hTT ppz
For small z_T: Volume emission
vacuumch
Lmediumch
LAAch DeDeD /
//
// )1(
At small z_T: both contribute
3.0Tz
16
The averaged distance <L> for the gamma-triggered parton jets passing through the quark matter.
Surface versus Volume emission
Small zt probes the matter deeper than large zt, so more sensitive.
Surface emission
Volume emission
3.0Tz
9.0Tz
17
Data from “A. Hamed for
STAR, talk at QM2008”
18
Single hadron Dihadron Photon-hadron
More sensitive probe?
NLO
19
Small-zt gamma-jets vs single jets
Gamma-jet Single jetsmall zT
Gam-jets for small zt probes the matter deeper than single jets.
3.0Tz 9.0Tz
20
Small-zt gamma-jets vs dijets
Gamma-jet Dijetsmall zT
Because of punch-through jets for dihadrons, it is not sure that small-zt gam-jets are more sensitive than dijets.
3.0Tz
9.0Tz3.0Tz 9.0Tz
21
Comparisons between gamma-h and dihadron in pp/AuAu
T
hh
hTrigT
h
Trig dz
dN
Nvs
dz
dN
N
11
)()(
)()(
ThAuAuT
hhAuAu
ThppT
hhpp
zDzD
zDzD
e.g. Trig=8GeV, zt=0.5
hadr:8 jet:12 jet:12 assoc: 4
gamm:8 jet:8 assoc: 4
p+p: Per trigger
22
Data from “A. Hamed for
STAR, talk at HP2008”
T
hh
hTrigT
h
Trig dz
dN
Nvs
dz
dN
N
11
)()(
)()(
ThAuAuT
hhAuAu
ThppT
hhpp
zDzD
zDzD
e.g. Trig=8GeV, zt=0.5
hadr:8 12 12 assoc: 4
gamm:8 8 6 assoc: 4
Au+Au: Per trigger
Volume emission
Tangential ~pp
Comparisons between gamma-h and dihadron in pp/AuAu
23
III. Conclusions
1) The suppression factor for hadrons with large z_T is controlled mainly by the surface emission of the gamma-jet events, while small z_T region will be volume emission bias.
2) Gamma-jets for small z_T region probe the dense matter deeper than those for large z_T region, so the gamma-jets for small z_T region are slightly more sensitive to the dense matter properties.
Thank for your attention!
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Thank for your attention!
谢谢!
25
Dominated by jets close and perpendicular to the surface
Dominated by dijets close and tangential to the surface and the
punch-through dijets
dihadron
Color strength: single/dihadron yield from the jets originating from the square
Thickness of the outer corona
single hadron
Spatial transverse distribution of the initial parton production points that contribute to the single and dihadron along a given direction at RHIC
25% contribution
26
1) No parton jet energy loss
2) Isospin effects
3) Shadowing effects
NLO direct photon in central Au+Au at RHIC
),(1),(),,(),,( 2
/2
/2
/2
/ xfA
Zxf
A
ZrxSrxf napaAaAa
Data from “PRL. 98 (2007) 012002”
27
For large z_T,
vacuumch
mediumchLL
vacuumch
vacuumch
Lmediumch
L
ppch
AAch
AA
vacuumch
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LAAch
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LLOAA
vacuumch
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AA
NLOmediumch
LOmediumch
eI
D
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DD
“NLO I_AA ” > “LO I_AA” for large z_T
28
Parton jet energy loss per unit length:
),(5.0
),/5.7/()6.1/( 02.1
01
partpartd
NsdN
dNEE
dL
dE
E. Wang , X. -N. Wang , PRL87(2001)142301)
B. B. Back for PHOBOS, nucl-ex/0604017v1
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0
0
part
part
Nsf
Nsf
Initial gluon density coefficient
Energy loss parameter
),(5.0
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00
partpart
part NsdN
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(a parameterization form of theory calculations)