Transcript 格点场论与Monte Carlo模拟
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 I.
II.
Introduction Analysis on photon-hadron correlations III. Conclusion The international workshop for QCD/HIC
1
July 10-12 , 2008
I. Introduction
What happens for a jet propagating inside QGP?
Jet quenching:
X.-N.Wang and M.Gyulassy, Phys.Rev.Lett.68,1480(1992) The hard jet loses a significant amount of its energy via radiating gluon induced by multiple scattering.
hadrons q hadrons q leading particle leading particle
N-N collision
hadrons q q hadrons leading particle suppressed
A-A collision
Leading particle suppressed
2
Three kinds of hard probes of QGP 1) 2) 3) Single jet
Single hadron spectra Dijet
Hadron-triggered away-side hadron spectra 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 ?
3
Motivation 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.
D AA
(
z T
) 1
N AA
h dN AA dz T
dp T
dy
dy h d
dp T
dy
p T
d
h AA
d
AA
/
dp T
dp T h dy
dy h d
/
dp T
dy
where z T
p T h
/
p T
.
I AA
(
z T
)
D AA
(
z T
)
D pp
(
z T
)
The sensitivity of Gamma-jets to probe the dense matter.
4
Gamma-jet by NLO pQCD parton model
d
AA
T AB
PDFs
d
FFs p T
LO: NLO corrections: (e.g. 2
3)
Jet p Gam T p T Gam p T Jet
1
p T Jet
2
p T Jet p T Jet p T Jet
p T Gam
,
p T Gam
,
p T Gam p T Jet
p T Gam p T Jet
One of
(
p T Jet
1 ,
p T Jet
2 )
therefore leading to hadrons with transverse momentum larger than that of the photons
5
The fragmentation of the jets off the dense matter
D h
/
c
(
z c
, 2 ,
E c
) ( 1
e
L
/
z
)[
z c
'
c D h
0 /
c
(
z c
' , 2 )
L
/
z
'
g D h
0 /
g
(
z
'
g
, 2 )]
e
L
/
D h
0 /
c
(
z c
, 2 )
z z c
'
p T
/(
p Tc
E c
),
z g
'
L
/
p T
/
E c
,
(X. -N. Wang , PRC70(2004)031901)
L
0 0
L d
0 0
g
( ,
b
,
r
n
),
The jet energy loss in a 1D expanding system:
0 1 / 0
E c
dE dL
1
d
0 0
L d
0 0 0
g
( ,
b
,
r
n
)
dE dL
1
d
0 (
E
/ 0 1 .
6 ) 1 .
2 /( 7 .
5
E
/ 0 )
Energy loss parameter (a parameterization form of theory calculations) Enke Wang , X. -N. Wang , PRL87(2001)142301)
r
6
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
LO NLO Annihilation Compton 2
3 one-loop J. F. Owens, Rev. Mod. Phys. 59, 465(1987); H. Baer, J. Ohnemus, and J. F. Owens, Phys. Rev. D. 42, 61(1990)
7
2)
Fragmentation
(bremsstrahlung) contributions
(accompanied by nearly collinear hadrons on the same side) Most accompanying hadrons are within a cone of half-angle
R cone
J. F. Owens, Rev. Mod. Phys. 59, 465(1987); H. Baer, J. Ohnemus, and J. F. Owens, Phys. Rev. D. 42, 61(1990)
8
Isolated photons in p+p at RHIC isolation cuts (IC):
R cone
0 .
5
rad
.,
E T
/
p
T
0 .
1
PRL 98 (2007) 012002 Because of IC selected at RHIC, most fragmentation contributions from parton jets are taken out. The left are mainly from annihilation and Compton processes, direct photon .
9
Focus on isolated photons now
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 !!!
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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High p_T direct photon dominates in central Au+Au at RHIC
Turbide, Gale, Jeon, Moore, Phys. Rev. C. 72 (2005) 014906
Per-trigger yield for photon-hadron production in p+p Per-trigger yield as a function of the p_T of the triggered photon:
h
dy
dp T h dy h
dy
dN dp
T dN dy
pp dp T
dy
pp dp T h dy h
NLO pQCD results describe the behavior of the data for photon-hadron produced in p+p at 200GeV Data from “Matthew Nguyen for PHENIX, talk at QM2008”
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Per-trigger yield for photon-hadron in central Au+Au NLO
D AA
(
z T
)
N
1
AA
h dN AA dz T
dp T
dy
dy h d
dp T
dy
p T
d
h AA
d
AA
/
dp T
dp T h dy
dy h d
/
dp T
dy
where z T
p T h
/
p T
.
I AA
(
z T
)
D AA
(
z T
)
D pp
(
z T
)
LO Qualitatively, Iaa in small z_T region is slightly more sensitive to epsilon_0 than Iaa in large z_T region.
Why?
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NLO N
h > 0 at z_T>1: surface emission
D h AA
/
c
( 1
e
L
/ )
D h medium
/
c
e
L
/
D h vacuum
/
c
0
z T
p T h p T
At large z_T: medium contributions vanish due to jet quenching, dominated by vacuum contributions.
z T
0 .
9
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.
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For small z_T: Volume emission
D h AA
/
c
( 1
e
L
/ )
D h medium
/
c
e
L
/
D h vacuum
/
c
At small z_T: both contribute
z T
0 .
3
z T
p T h p
T
15
Surface versus Volume emission The averaged distance
z T
0 .
3
Volume emission
z T
0 .
9
Surface emission Small zt probes the matter deeper than large zt, so more sensitive.
16
Data from “A. Hamed for STAR, talk at QM2008”
17
Single hadron Dihadron Photon-hadron NLO More sensitive probe?
18
Small-zt gamma-jets vs single jets
z T
0 .
3
z T
0 .
9
small z T Gamma-jet Single jet Gam-jets for small zt probes the matter deeper than single jets.
19
z T
0 .
3
Small-zt gamma-jets vs dijets
z T
0 .
9
z T z T
0 .
3 0 .
9
small z T Gamma-jet Dijet Because of punch-through jets for dihadrons,
20
it is not sure that small-zt gam-jets are more sensitive than dijets.
Comparisons between gamma-h and dihadron in pp/AuAu
1
N Trig dN
h dz T vs
1
h N Trig dN hh dz T D hh pp
(
z T
)
h D pp
(
z T
)
hh D AuAu
(
z T
)
h D AuAu
(
z T
)
e.g. Trig=8GeV, zt=0.5
hadr:8
jet:12 jet:12
assoc: 4
p+p:
Per trigger gamm:8
jet:8
assoc: 4
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Comparisons between gamma-h and dihadron in pp/AuAu
1
N Trig dN
h dz T vs
1
h N Trig dN hh dz T D hh pp
(
z T
)
h D pp
(
z T
)
hh D AuAu
(
z T
)
h D AuAu
(
z T
)
Data from “A. Hamed for STAR, talk at HP2008”
e.g. Trig=8GeV, zt=0.5
hadr:8
12 12
assoc: 4
Au+Au:
Per trigger gamm:8 Volume emission 8
6
assoc: 4
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!
23
Thank for your attention!
谢谢！ 24
Spatial transverse distribution of the initial parton production points that contribute to the single and dihadron along a given direction at RHIC Color strength: single/dihadron yield from the jets originating from the square Dominated by jets close and perpendicular to the surface Dominated by dijets close and tangential to the surface and the punch-through dijets single hadron dihadron Thickness of the outer corona 25% contribution
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NLO direct photon in central Au+Au at RHIC 1) No parton jet energy loss 2) Isospin effects Data from “PRL. 98 (2007) 012002” 3) Shadowing effects
f a
/
A
(
x
, 2 ,
r
)
S a
/
A
(
x
, 2 ,
r
)
Z A f a
/
p
(
x
, 2 ) 1
Z A f a
/
n
(
x
, 2 ) 26
“NLO I_AA ” > “LO I_AA” for large z_T
I D h AA
/
c AA
~ ( 1
e
D D h h AA
/
pp
/
c c
L
/ ( 1 )
e D h
medium
/
c L
/
e
L
/ )
D h medium
/
c
D h vacuum
/
c D h vacuum
/
c e
L
/
D h vacuum
/
c
e
L
/ ( 1
e
L
/ )
D h medium
/
c D h vacuum
/
c
For large z_T,
(
D h medium
/
c
)
LO NLO I AA
e
LO I AA
L
/ 0 ,
e
L
/ (
D h medium
/
c
)
NLO
0 ( 1
e
L
/ )
D h medium
/
c D h vacuum
/
c
27
Parton jet energy loss per unit length: (a parameterization form of theory calculations) E. Wang , X. -N. Wang , PRL87(2001)142301)
dE dL
1
d
(
E
/ 0 1 .
6 ) 1 .
2 /( 7 .
5
E
/ 0 ),
dN
0 .
5
N part d
(
s
,
N part
) 0
f
( 0
f
(
s
,
N part
)
s
,
N part
)
Energy loss parameter
0 0
Initial gluon density coefficient
f
(
s
,
N part
)
dN
0 .
5
N part d
(
s
,
N part
)
B. B. Back for PHOBOS, nucl-ex/0604017v1