Angular resolution study of isolated gamma with GLD detector simulation

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Angular resolution study of isolated gamma with
GLD detector simulation

• 2007/Feb/5
• ACFA ILC Workshop
• M1 ICEPP, Tokyo
• Hitoshi HANO
• On behalf of the Acfa-Sim-J Group

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Contents

• Introduction
• Angular Resolution Study
• Position Resolution of ECAL cluster
• Direction of Reconstructed gamma
• Calorimeter Component Dependence
• Cell size Dependence
• Material Dependence
• Summary

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Motivation and PFA Analysis

• Measurement of the direction of non-pointing
  photon is important for GMSB (gauge mediated
  supersymmetry breaking) scenarios.

decay length
m

• To identify a non-pointing photon, we need to
  know angular resolution of the detector (EM
  Calorimeter).

We have studied angular resolution using
full-simulator (Jupiter)
ECAL
In this study, we have used single-gamma coming
from IP to evaluate angular resolution.
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GLD Detector Geometry in Jupiter

• GLD detector has large-radius and fine-segmented
  Calorimeter.

Calorimeter cell size and absorber material can
be changed.
Its important to optimize Cost
vs.
Physics Performance.
ECAL geometry in Jupiter
R m
Z m
Structure
W/Scinti./gap3/2/1(mm) x 33 layers cell size
1x1(cm2)
barrel endcap
2.1-2.3 0.4-2.3
0-2.8 2.8-3.0
ECAL
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Method of Gamma Reconstruction

• Clustering
• Find an energy-weighted central point of each
  layer
• Fit each point with least-square method
• Evaluate an angle between gamma-line and
  reconstructed gamma

Calorimeter
?
IP (generated point)
reconstructed gamma
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Angular Resolution Study
Position Resolution of Cluster
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Method (position resolution study of aaaaaaa
isolated gamma cluster)

• Generate single-gamma from IP with random
  direction
• Clustering (more details in next page)
• Search energy-weighted central point of cluster
• Evaluate ?, f of a central point
• Compare with MC truth

ECAL
central point
(?,f)
IP (generated point)
?
clustering
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Clustering Method

• Find the highest energy deposit cell
• Make a cone around the cell
• Define cells which are inside of the cone as one
  cluster (around all layers)
• Find energy-weighted central point

highest energy deposit cell
central point
clustering angle 10
IP (generated point)
?_at_10GeV
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Position Resolution of Cluster (cell 1 cm)
barrel
endcap
endcap
barrel
1 GeV 2 GeV 5 GeV 10 GeV
s mrad
s mrad
cos(?)
cos(?)
? resolution is better for larger cos(?)
f resolution is worse for larger cos(?)
ECAL
geometrical effect
Position resolution 0.1 cm
IP (generated point)
gamma_at_10GeV
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Energy Dependent Result of position resolution
1GeV
2GeV
s mrad
s mrad
5GeV
10GeV
1/vE
1/vE
? barrel
f barrel
mrad
mrad
? endcap
f endcap
mrad
mrad
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Angular Resolution Study
Direction of Reconstructed gamma
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Method (angular resolution study of
reconstructed gamma)

• Clustering
• Find an energy-weighted central point of each
  layer
• Fit each point with least-square method
• Evaluate an angle between gamma-line and
  reconstructed gamma

Calorimeter
?
IP (shot point)
reconstructed gamma
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Histogram and Angular Resolution
?
central point of cluster
IP
d
r
reconstructed gamma
angle rad r/d

• r histogram F(r)

fitting function
s 48.3 0.3 mrad
gamma_at_10GeV
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Energy Dependence (1,2,5,10,50GeV)
1GeV
2GeV
s mrad
Average over full acceptance
10GeV
5GeV
50GeV
1/vE
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Shoot from another point gamma_at_10GeV

• Shoot from IP

• Shoot from xy20cm, z0

reconstructed gamma
IP
ECAL
s 48.30.3mrad
s 48.60.3mrad
If gamma has been shot from another position,
we could not observe significant
difference.
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Calorimeter Component Dependence
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Structure (cell size dependence)
gamma E 10GeV
33 layers
How about cell size dependence?
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Cell size dependence
1 cm 48.3 0.3 mrad 0.5 cm 46.4
0.3 mrad
gamma _at_10GeV
lt5
We could not observe significant improvement from
1cm to 0.5cm
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Structure (energy dependence)
gamma E 110GeV
33 layers
How about energy dependence between 1cm and 0.5cm?
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Energy Dependence (1,2,5,10GeV)
1GeV
2GeV
5GeV
10GeV
No significant difference has been observed
between 1cm and 0.5cm around all of energy.
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Structure (Absorber dependence)
gamma E 10GeV
33 layers
How about absorber dependence?
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Absorber Dependence (Tungsten, Lead)
Tungsten3mm
Lead4.8mm
Same total radiation length
Lead3mm
Tungsten 3mm 48.3 0.3 mrad Lead 4.8mm
45.5 0.3 mrad
_at_1x1 cm
Angular resolution with Lead is better than
Tungsten
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Hit Distribution
reconstructed gamma
Angular resolution is better than Tungsten,
since shower length is longer in Lead
gamma MC
depth
gamma MC
reconstructed gamma
depth
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Summary

• Angular resolution of default-GLD Calorimeter
  (W1cm)
• The angular resolution is estimated to be
  125mrad/v(E/GeV)
• Dependence on cell size granularity and material
  dependence (W, Pb) has been studied
• No significant difference has been observed
  between 1cm and 0.5cm
• Lead is better than Tungsten for isolated gamma
• Energy resolution is same
• How about energy resolution for jet ?

Next speaker T.Yoshioka
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Backup
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Fitting method
Find a central point of each layer by energy
weighted mean
Fitting 2-dimentions (x-y)
y
y
x
Fitting new 2-dimentions (y-z)
weighted by energy deposit
z
y
Distancecm
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Hitting distribution and Average
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Hit Distribution
reconstructed gamma
gamma MC
gamma MC
reconstructed gamma
depth
depth
Angular resolution is better than Tungsten,
since Lead has geometrical deeper distribution.
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