PHENIX measurements of reaction plane dependence of high p T photons and pions in Au+Au collisions...
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Transcript of PHENIX measurements of reaction plane dependence of high p T photons and pions in Au+Au collisions...
PHENIX measurements of PHENIX measurements of reaction plane dependence of reaction plane dependence of high phigh pTT photons and pions in photons and pions in
Au+Au collisionsAu+Au collisions
Vladislav Pantuev, University at Stony Brook
for PHENIX collaboration
Outline:
Part 1. Direct photons
• Motivation
• Method
• Results
Part 2. High pT neutral pion suppression and reaction plane angular dependence
• RAA and Partial energy loss
• Reaction plane dependence
• Possible explanation
Conclusion2
Part 1. Direct photons. Motivation
Why in this case Why in this case we are looking for we are looking for any angular any angular dependence?dependence?
High-High-ppTT direct photons direct photons
produced in initial hard produced in initial hard parton-parton scatteringsparton-parton scatterings
Low Low ppTT thermal photons thermal photons
expected to reflect the expected to reflect the initial temperature of the initial temperature of the fireballfireball
Photons leave the Photons leave the subsequently produced subsequently produced medium unalteredmedium unaltered
Leading Particle
Direct
Hadrons
gq
frag.
3
There are theoretical predictions with a There are theoretical predictions with a sizable azimuthal parameter v2 :sizable azimuthal parameter v2 :
S.Turbide, C.Gale, R.J.Fries, PRL 96 032303 (2006)
R. Chatterjee et al., PRL 96, 202302 (2006)
Thermal photons are produced throughout the expansion history and reflect quark anisotropy
Jets lose more energy where the medium is thicker - more jet-photon conversions (v2<0), + photons from fragmentation of quenched jets (v2>0)
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How does PHENIX measure direct photons and v2?
Measure inclusive photon yield, Ninc
Measure hadron contribution components 0 and By Monte Carlo calculate and decay background in
inclusive sample, Nbg
Calculate direct photon excess over hadron decays, R Measure inclusive and hadron v2 by reaction plane
method Calculate direct photon v2 as
R * v2inc – v2
BG
R = N inc / NBG
v2dir =
R – 1
Use large statistics Run 4 Au+Au data set
See also poster 86 by Kentaro Miki 5
Step by step calculations:
PHENIX preliminary
PHENIX preliminary
PHENIX preliminary
PHENIX preliminary
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PHENIX direct photon v2 result
Within statistical and systematic errors v2 is consistent with
zero. v2=0 or cancellation of different contributions?
Systematic errors dominantly from R:
Enormous background of decay photons at low pT
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Part 2. Neutral pion suppression and azimuthal anisotropy
Suppression of high pt pions is in favor of energy loss of hard partons
On the other hand, this canonical view is in trouble to describe heavy quark suppression
Clearly, inclusive particle spectra are not sufficient to validate or exclude different models
Centrality dependence of RAA is an effective estimator of path length dependence for energy loss, but
It is more precise to vary path length keeping the same medium conditions: select different angles versus the reaction plane of the event
See PHENIX paper nucl-ex/0611007, submitted to PRC8
PHENIX Run 2 final 0 results.Level-2 trigger data – factor 3 more statistics
Nuclear modification factor:
Systematic error
Factor of ~5 0 suppression at high pT
Approximately constant with pT
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PHENIX, nucl-ex/0611007, submitted PRC
Suppression as spectrum shift: shift in momentum by fractional energy loss of primary parton
At high pT spectra are linear
and parallel in log-log scale
Power law shape, ~PT-n
More details in nucl-ex/0611007, submit PRC
Can calculate average fractional parton energy loss:
Original momentum of parton:
10
In agreement with model estimations by:
Calculate Sloss from RAA :
In average, parton loses 15-20% of its original energy in most central Au+Au events
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Pion absorption versus angle w.r.t. reaction Pion absorption versus angle w.r.t. reaction plane – plane – other way to control thickness of the other way to control thickness of the mediummedium
Centrality 40-50%At fixed centrality change parton path length by varying and keeping the same :
•Initial conditions
• Longitudinal and transverse expansion
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The results:
3 < pT < 5 GeV/c 5 < pT < 8 GeV/c
-RAA in plane and out of plane changes by factor ~2
- For peripheral bins no suppression in plane, while a factor ~2 out of plane
PHENIX Run2, nucl-ex/0611007, submitted PRC
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We vary path length by centrality and angle , both results should agree
Colors represent different centralities
RAA is universal function of L
Sloss is universal and linear with L
RAA~1 and no energy loss for L < 2 fm
Variable 1 : simply L, distance
from the center of interaction region to the edge
60-70%
10-20%
Flow contribution up to 8 GeV/c?
Cronin effect?
Something else?
See D. Winter poster 47, Run4 data, preliminary 14
Surprising, variables like L, L2, Lxy (see
details in nucl-ex/061107) do not work so well:
15
Why no absorption? Alternative explanation: Time matters!
Let jets fly in ANY direction:
Ncoll distribution in transverse plane, Glauber + Woods-Saxon
Stop jet after some time T.
T =2.3 fm/c to fit peripheral data
see my poster 32 and hep-ph/0506095
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The result:
Results of calculation
Describes inclusive RAA and dependence
v2=11% at high pT,
Simple explanation of lack of absorption in a layer < 2 fm,
some other features
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From V.P. hep-ph/0506095
Conclusions:Conclusions:
Within errors direct photon azimuthal asymmetry is consistent with zero
As in previous papers we observe a factor of ~5 0 suppression at high pT, approximately constant with pT
We see factor ~2 suppression for out of plane compared to in plane
RAA~1 or there is no jet absorption if the medium size is less than 2 fm
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Twice better reaction plane resolution in Twice better reaction plane resolution in upcoming Run 7 with new reaction plane upcoming Run 7 with new reaction plane
detectordetector
MC simulation
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backupbackup
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Green line is for Raa extracted with free expansion method.
Free streaming is automatically taken into account in the original assumptions
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22s
Can calculate elipticity parameter v2 as
jet surviving probability
in and out of plane
Data are for high pt pi0s, PHENIX,
blue cicles – 4.59 GeV/c,
green squares – 5-7 GeV/c, preliminary
No hydro/collective flow!
How to explain rising and falling down v_2 with momentum?
100%
0%
pt
core+hydro+exponent corona
Relative contribution
At low momentum hydro scenario produces most of particles and v2 increases with momentum.
At high pt, particles are produced from corona with smaller v2.
Corona contribution “dilutes” hydro v2 at mid pt to the value of geometry limit. Knowing corona contribution can correct for hydro 23v2
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Compton Annihilation
In p+p Hard photons:direct component
q + g +q q +q + g
Photons in A+A
Direct Photons Decay Photons
hard thermal hard+thermal
QGP Hadron gasdirect fragmentation
Preequilibriumphotons
jet--conv.
Medium induced bremsstr.
In A+A picture is much more complicated:
V2=0V2<0V2<0
V2>0V2>0V2>0