Event by Event Isolated Photon Identification in PHENIX EMCal

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Event by Event Isolated Photon Identification
in PHENIX - EMCal

• Gine MARTINE , SUBATECH
• (CNRS/IN2P3 EMN - Université de Nantes)
• Nantes, FRANCE

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Preface

• This is a short presentation about the PHENIX
  EMCal capabilities to identify high pT photons.
• PISA simulation results.
• I know QM2002 new results are more interesting.
• But, we are in Palaiseau and we have to make a
  full afternoon of French PHENIX presentations.
• An analysis note soon.
• Good reading after QM2002.

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Motivations Reality

• We want to measure direct photons.
• pT range 1 25 GeV/c
• We want to reject meson decay photons.
• we can always dream
• The kinematics of the electromagnetic meson decay
  is what it is.
• The electromagnetic calorimeter is a real
  detector.
• Acceptance, Thresholds, Reconstruction, PID, etc
  
• Our environment is not very  clean .
• Large Combinatorial Background, High Multiplicity
  Environment.

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Outlook

• Kinematics
•  Maximum Asymmetry  Parameter
• Algorithm Spectroscopic Isolation Cut Analysis
  (SIC)
• Isolated percentage ISOLATED/CANDIDATES
• Flat distribution
• Power-law distribuion
• p0 energy estimation.
• Energy Threshold.
• High Multiplicity Environment.
• Direct Photon Excess Extraction.
• Conclusions.

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Kinematics of the p0 decay
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Relative Opening Angle
Relative opening angle (rad)
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Asymmetry Parameter

• Looking for a companion photon within a 100
  acceptance disk Cone inside EMCal
• Invariant Mass Analysis Spectrometer better than
  Calorimeter (Spectroscopic).
• Asymmetry as a parameter amax
• Independent on p0 initial energy
• Asymmetry as probability
• Compromise Acceptance vs Rejection
• amax 0.6, 0.7, 0.8, 0.9 and 0.95

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The algorithm

• For each photon  i 
• Look if the disk (cone projection on EMCal) of
  radius Ri(amax(Ep)) around the center of the
  photon cluster, is inside EMCal
• if Yes ?  Photon Candidate 
• Looking for photon companion  j  for which the
  minvij100-160 MeV/c2.
• if No ?  Isolated Photon  (it could be a  fake
  direct  or a  real direct  photon).
• Studying the ratio
• Ratio (dNiso/dEg) / (dNcan/dEg)

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Mono energetic p0
amax 0.9, RatioNiso/Ncan0.1 amax 0.8,
RatioNiso/Ncan0.2
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Direct Photon Excess
p0
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Flat Distribution (E1 , E2)
Ratio Niso/Ncan
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PISA Simulations

• pT 0 - 12 GeV/c
• -0.5lt h lt0.5
• 0 lt j lt 2p
• Flat distribution
• Power Law 1/En,
• n7.02 (p0 _at_ 130A GeV)

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Flat p0 Simulation in EMCal
candidates
isolated
amax 0.6
amax 0.7
amax 0.9
amax 0.8
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Ratio for a Flat p0 Simulation
amax 0.6
amax 0.7
Ratio Niso/Ncan
amax 0.9
amax 0.8
Ratio Niso/Ncan
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Power Law Distribution
n7.02 AuAu _at_ 130A GeV
Ratio Niso/Ncan
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Power Law p0 Simulation
amax 0.6
amax 0.7
candidates
isolated
amax 0.9
amax 0.8
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Ratio for a Power Law
amax 0.6
amax 0.7
Ratio Niso/Ncan
amax 0.9
amax 0.8
Ratio Niso/Ncan
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Realistic Algorithm

• Initial p0 energy is unknown
• High Multiplicity environment
• Energy threshold of the detector

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p0 energy estimation
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With Without p0 energy estimation
FLAT
Ratio Niso/Ncan
Without
With
amax 0.7
amax 0.8
amax 0.9
amax 0.95
Ratio Niso/Ncan
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With Without p0 energy estimation
POWER LAW
Without
Ratio Niso/Ncan
With
amax 0.7
amax 0.8
amax 0.9
amax 0.95
Ratio Niso/Ncan
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High Multiplicity Environment

• Combinatorial Background Simulation
• Power law background
• 50 p0s per rapidity unit (peripheral)
• 300 p0s per rapidity unit (central)

Embedded (raw-rel mixing) with
The single p0 uniformly distributed, and
power-law weighted
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Low Occupancy (Peripheral)
amax 0.7
amax 0.8
Singles
Ratio Niso/Ncan
Embedded
amax 0.9
amax 0.95
Ratio Niso/Ncan
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High Occupancy (Central)
amax 0.7
amax 0.8
Singles
Ratio Niso/Ncan
Embedded
amax 0.9
amax 0.95
Ratio Niso/Ncan
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Threshold Energy
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Energy Threshold
amax 0.7
amax 0.8
Ratio Niso/Ncan
amax 0.9
amax 0.95
Ratio Niso/Ncan
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Realistic SIC Analysis

• Initial p0 energy is unknown
• High Multiplicity environment
• Energy threshold of the detector

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Realistic SIC p0 analysis (pp)
amax 0.7
amax 0.8
Ratio Niso/Ncan
amax 0.9
amax 0.95
Ratio Niso/Ncan
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Realistic SIC p0 analysis (periph)
amax 0.7
amax 0.8
Ratio Niso/Ncan
amax 0.9
amax 0.95
Ratio Niso/Ncan
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Realistic SIC p0 analysis (central)
amax 0.7
amax 0.8
Ratio Niso/Ncan
amax 0.9
amax 0.95
Ratio Niso/Ncan
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Realistic g SIC analysis (pp)
amax 0.7
amax 0.8
Ratio Niso/Ncan
amax 0.95
amax 0.9
Ratio Niso/Ncan
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Realistic g SIC analysis (periph)
amax 0.7
amax 0.8
Ratio Niso/Ncan
amax 0.95
amax 0.9
Ratio Niso/Ncan
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Realistic g SIC analysis (central)
amax 0.7
amax 0.8
Ratio Niso/Ncan
amax 0.95
amax 0.9
Ratio Niso/Ncan
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More about Photon Excess Extraction
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Photon Excess
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Conclusions

• High Photon Identification (SIC).
• Free parameter amax
• amax between 0.8-0.9
• Expected Ratio (fake direct) from p0 real data
  
• 0.4 - 0.7
• When can SIC be applied?
• Low occupancy
• pT gt 3 GeV/c for amax0.8
• pT gt 5 GeV/c for amax0.9
• High occupancy pT
• pT gt 5 GeV/c for amax0.8
• pT gt 7 GeV/c for amax0.9

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Quark Matter 2002
QM2002 Preliminary
Enjoy !
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Weather in Nantes