Upload
laken
View
64
Download
0
Embed Size (px)
DESCRIPTION
Direct Photon-Hadron Correlations in Au+Au at 200GeV. Megan Connors For the PHENIX Collaboration Quark Matter 2009. Photon tagged jets as probes. Photons do not interact strongly R AA ≈ 1 implies no medium effect - PowerPoint PPT Presentation
Citation preview
1
Direct Photon-Hadron Correlations
in Au+Au at 200GeV
Megan ConnorsFor the PHENIX Collaboration
Quark Matter 2009
2 M. Connors
Photon tagged jets as probes Photons do not interact
strongly
RAA≈1 implies no medium effect
γ-h correlations should be more sensitive to modified fragmentation function and energy loss than h-h γ energy ≈ jet energy
3 M. Connors
Photon Sources
q
qg
q
q g
γ
Compton Annihilation
γ
At high pT promptphotons dominate!
π0 suppression
Hadron decays Direct photons
Compton scattering 2 parton annihilation
Fragmentation Photons Final state partons
Jet-thermal annihilation Thermal radiation Bremsstrahlung
π0 γγ
Medium Induced
4 M. Connors
γ-jet Correlations
q
qg
γ
?
5 M. Connors
Measurements with Photon Tagged Jets
Also can measure IAA, ratio of the direct photon-hadron yields
zp
phad ro n
je t
D zN
dN zdzq
evt
( )( )
1
γ energy ≈ jet energy
X.N. Wang, Z. Huang PRC55 (1997) 3047-3061
IAA = YAA/Ypp~DAA(z)/Dpp(z)
6 M. Connors
Statistical Method for Determining the Direct Photon Yield
0-h decayed via MC to get decay -h
YN
dNd
h
1
( )
pT [GeV]
R
For Singles: Nincl = Ndirect + Ndecay
Y Y Yinc lNN direct
NN deca y
d irect
in cl
decay
in cl
R NN
NN
incl
decay
d irec t
decay 1YR Y Y
Rd irect
incl decay
1
For Pairs:
π0 pT [GeV]
7 M. Connors
γ-h Correlation Inclusive
Decay
Direct γ-h
YR Y Y
Rd irect
in cl deca y
1
8 M. Connors
Away-side Yields Measurements have shown suppression of
awayside (PHENIX arXiv:0903.3399)
Run 7~4X statistics
9 M. Connors
Run 7 Measurements Suppression and modified fragmentation
function
10 M. Connors
How much suppression? Ratio to p+p yields Average from Run4: IAA=0.32±0.12±0.09
arXiv:0903.3399
11 M. Connors
Modified Fragmentation Function
zppT
Th
T
D zN
dN zdzq T
evt
T
T( )
( )
1
γ pT ≈ jet pT
IAA ~DAA(zT)/Dpp(zT)
12 M. Connors
Surface emission? NLO, Longitudinal expansion Modification at low zT and suppression at high zT Zhang et al arXiv0902.4000v1
High zT
Low zT
13 M. Connors
Effect of Fluctuations
Priv. comm.
LO, 3D hydro ASW Includes
probability function instead of an average energy loss
Result: Reduces the
geometric dependence
Flatter IAA vs zTT. R. and K. Eskola, Phys. Rev. C 75 (2007) 054910;T. R., Phys. Rev. C 78 (2008) 034904
14 M. Connors
Enhanced Low zT Multiplicity
ln
1z T
Analytic MLLA Radiative Energy
loss results in enhancement of soft particle multiplicity
Ratio of medium/vacuum curves is IAA
Borghini and Wiedemann arXiv:hep-ph/0506218
ln
1z T
15 M. Connors
The Comparison Exhibits the
biggest zT dependence
Expanded awayside integration region
Borghini and Wiedemann arXiv:hep-ph/0506218
16 M. Connors
Compare to 0-h Similar suppression in direct -h and 0-h!
See A. Adare’s Posterz
ppT
Th
Ttrig
17 M. Connors
Fragmentation Function Measurement of modified FF in Au+Au compared
to p+p
18 M. Connors
Slope comparisondNdz
N eT
bz T
Fit a universal curve for all jet energies
p+p slope of 6.89 ± 0.64 more consistent with quark fragmentation of b=8 than b=11 for gluons
Slope of Au+Au is 9.49 ±1.37
Au+Au slope is ~1.3σ higher than p+p
19 M. Connors
Near Side Story Approximately zero direct γ–h yield in Au+Au No enhancement compared to p+p direct γ–h
20 M. Connors
Conclusions Moving toward precision measurements of
Energy loss Similar suppression as seen in 0-h Au+Au zT distribution appears steeper
than p+p No enhanced nearside yield observed
Not yet the final word on direct γ-h
21 M. Connors
How we measure γ–h correlations
Trigger on a high pT (>5GeV/c) inclusive photon Measure between photon and all hadrons
in the event within a certain pT range Event mixing corrects for acceptance and
combinatorial pairs
Δφ
Drift Chamber
Per-
Trig
ger Y
ield
Underlying Event =Combinatorial Bknd +Elliptic Flow
PbSc
Electromagnetic Calorimeters
PbGl