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Realistic Particle Flow Algorithm for GLD. T.Yoshioka (ICEPP) , M-C.Chang(Tohoku), K.Fujii (KEK), T.Fujikawa (Tohoku), A.Miyamoto (KEK), S.Yamashita (ICEPP), on behalf of ACFA-SIM-J Group. Contents : 1. Introduction 2. Procedure of PFA - Small Clustering - Gamma Finding - PowerPoint PPT Presentation
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7/13/2005 The 8th ACFA Workshop@EXCO, Daegu, Korea
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T.Yoshioka (ICEPP), M-C.Chang(Tohoku), K.Fujii (KEK),T.Fujikawa (Tohoku), A.Miyamoto (KEK), S.Yamashita (ICEPP),
on behalf of ACFA-SIM-J Group
Realistic Particle Flow Algorithmfor GLD
Contents :1. Introduction2. Procedure of PFA
- Small Clustering- Gamma Finding- Track Matching
3. Results4. Summary
7/13/2005 The 8th ACFA Workshop@EXCO, Daegu, Korea
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Introduction- Most of the important physics processes studied in the future linear collider experiments have multi-jets in the final state.
→ Precise Jet reconstruction is essential.
- Since the momentum resolution of the charged particle is much better than the energy resolution of the calorimeter, we use
Trackers for charged particlesCalorimeters for neutral particles
for Jet reconstruction. → Particle Flow Algorithm (PFA)
- In this talk, we present a performance of the PFA using a full simulator of GLD named Jupiter.
7/13/2005 The 8th ACFA Workshop@EXCO, Daegu, Korea
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- End view
Thanks to Y.Yamaguchi (Tsukuba)
- Side view
Barrel Tower Front : 210cm Endcap Inner R : 40cm Endcap Tower Front Z : 270cm
Calorimeter Geometry in Jupiter
40 cm270 cm
210 cm 210 cm
- Consists of tower structure.
7/13/2005 The 8th ACFA Workshop@EXCO, Daegu, Korea
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Thanks to Y.Yamaguchi (Tsukuba)
- Tower
- # of Layers ECAL : 38 HCAL : 130
- Side view
Barrel Tower Front : 210cm Endcap Inner R : 40cm Endcap Tower Front Z : 270cm
Calorimeter Geometry in Jupiter
40 cm270 cm
210 cm
Full One Tower ECAL + HCAL
ECAL
HCAL
7/13/2005 The 8th ACFA Workshop@EXCO, Daegu, Korea
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Thanks to Y.Yamaguchi (Tsukuba)
- Cell
- Cell Size EM : 4cm x 4cm HD : 12cm x 12cmCan be changed easily.
- Tower
- # of Layers ECAL : 38 HCAL : 130
- Side view
Barrel Tower Front : 210cm Endcap Inner R : 40cm Endcap Tower Front Z : 270cm
Calorimeter Geometry in Jupiter
40 cm270 cm
210 cm
Full One Tower ECAL + HCAL
27 X0
6.1λ
ECAL
HCAL
7/13/2005 The 8th ACFA Workshop@EXCO, Daegu, Korea
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Energy Deposit in a Cell
ECAL HCAL
- Z → qq-bar(q = u,d,s)@91.187GeV.
7/13/2005 The 8th ACFA Workshop@EXCO, Daegu, Korea
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PFA Procedure
1.Small Clustering (collect fired cells with its neighbors) → Define thrust and broadening for each small cluster.2. Gamma Finding (Separate gamma/e to hadron) → Small Cluster based.3. Cluster-Track Matching (Separate charged to neutral) → Calorimeter Cell based.
Note: → Cheating method is used for charged hadrons in
the Endcap region. → Assuming the remaining clusters be neutral hadrons.
Flow
to make P
FO
bject
- Current Scheme of the PFA
7/13/2005 The 8th ACFA Workshop@EXCO, Daegu, Korea
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Small Clustering
(1) Find the “starting cell” among those “fired cell” in ECAL and HCAL which contains the highest energy deposition.(2) From the “starting cell”, find its “fired” neighbor cells to form a small cluster.
Starting Cell(Highest energy cell)
Neighbor Cells“Fired” = edep>50keV
If the cluster energyexceeds 50MeV(beforecalibration), the clusteringis stopped.
7/13/2005 The 8th ACFA Workshop@EXCO, Daegu, Korea
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Small Cluster Distributions
Number of hitsin a small cluster
Small ClusterEnergy
- Z → qq-bar(q = u,d,s)@91.187GeV.
7/13/2005 The 8th ACFA Workshop@EXCO, Daegu, Korea
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Variables for Small Cluster
i i
i ii
i i
i ii
X
EnXB
X
EnXT
||
||
||
||
- Energy-weighted Thrust & Broadening
Center of thesmall cluster
Thrust axis (n)Direction from the center to each hit (Xi)
- Thrust axis n is defined as to maximize the T.
Small Cluster
7/13/2005 The 8th ACFA Workshop@EXCO, Daegu, Korea
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Thrust and Broadening
Thrust Broadening
- Z → qq-bar(q = u,d,s)@91.187GeV.
7/13/2005 The 8th ACFA Workshop@EXCO, Daegu, Korea
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Gamma Finding Procedure
(1) Fit the longitudinal profile of the energy deposit of a small cluster as an electromagnetic cascade.(2) Make a cut on the distance from the nearest track.(3) Compare energy sum between HCAL/ECAL within a tube.
Details of the gamma finding algorithm/performance are describedby next speaker (T.Fujikawa)
So far, we achieved Efficiency : 60%, Purity : 99%.
7/13/2005 The 8th ACFA Workshop@EXCO, Daegu, Korea
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Track Matching Procedure- Basic Concept : Extrapolate the charged track and calculate a distance between a calorimeter hit cell and the extrapolated track. Connect the cell that in a certain tube radius (clustering).
Charged TrackCalorimeter input position
Hit Cellsdistance
ECAL
HCAL
- Tube radius for ECAL and HCAL can be changed separately.
- Calculate the distance for any track/calorimeter cell combination.
Extrapolated Track
Tube Radius
7/13/2005 The 8th ACFA Workshop@EXCO, Daegu, Korea
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Track Matching Procedure
(1) Sum up calorimeter cell energies within a tube for a track (Ecluster).(2) If Ecluster > Etrack x (0.4 x nsigma + 1), stop the clustering for the track. If not, perform (1) for each track. (We assume the calorimeter resolution of 40%.)(3) Widen the tube radius (only a Rstep) and perform (1) and (2) again.(4) Perform (1)-(3) until the tube radius reach the max radius (Rmax).
Parameters (nsigma, Rstep and Rmax) should be optimized.
- More detail of the procedure…
7/13/2005 The 8th ACFA Workshop@EXCO, Daegu, Korea
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Distance Distribution
ECAL HCAL
- Z → qq-bar(q = u,d,s)@91.187GeV.
7/13/2005 The 8th ACFA Workshop@EXCO, Daegu, Korea
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Efficiency/Purity- Efficiency/Purity of Track Matching is checked by cheating method.
Efficiency : 86.4% Purity : 82.2%
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Event Display
e+
e-
Just in order to get a feelingof current procedure…
7/13/2005 The 8th ACFA Workshop@EXCO, Daegu, Korea
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Event Display
Z → qq-bar
Red : pionYellow : gammaBlue : neutron
e+
e-
7/13/2005 The 8th ACFA Workshop@EXCO, Daegu, Korea
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Event Display
At first, charged hadrons in Endcap regionare removed by cheating method.
7/13/2005 The 8th ACFA Workshop@EXCO, Daegu, Korea
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Event Display
After Endcap cheating…
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Event Display
In the next, e/gamma like clustersare removed by “Gamma Finding”.
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Event Display
After e/gamma finding…
Note Efficiency : 60%Purity : 99%
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Event Display
Then, Then, calorimeter hits near the extrapolatedtrack are collected by “Track Matching”.
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Event Display
Remaining clusters are assumedto be neutral hadrons.
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Z Energy Resolution
Sum up Calorimeter Energy Particle Flow Algorithm
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Change Calorimeter Cell SizeEM : 4cm x 4cmHD : 12cm x 12cm
EM : 1cm x 1cmHD : 1cm x 1cm
- In the current method, the resolution is not improved so much by fine segmentation. → Another method should be considered in this case. (tracking and vertex finding in calorimeter, etc…)
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Can We Improve More?
pn
K
pi
KL
e/gamma: EC cheating: e/gamma finding: track matching: remaining hits
Particle ID of hit cell- Current e/gamma finding efficiency is ~60%. → Improve efficiency while keeping high purity.
- There are still ~10% charged hadrons after track matching. → Optimize parameters (Tube radius etc…)
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e/gamma Contamination
Track matching purity
Track matching purity w/o e/gamma
- If e/gamma contamination are removed (by cheating), the track matching purity improve from 82.2% to 92.2%.
→ Z energy resolution would also be improved.
7/13/2005 The 8th ACFA Workshop@EXCO, Daegu, Korea
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Track Matching Performance- Collected calorimeter energy minus track energy
- Lower tail indicates that current tube radius is narrow (not efficiently collected energy).
1. Optimize parameters.
2. Energy dependent tube radius?
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Summary and Future
- Realistic Particle Flow Algorithm (PFA) for GLD is developed and the performance is checked.
- Gamma Finding : Efficiency : 60%, Purity : 99%(Details will be presented by T.Fujikawa)
- Track Matching : Efficiency : 86.4%, Purity : 82.2%- Z energy resolution : 40%/sqrt(E)
- Goal : 30%/sqrt(E) of Z energy resolution.- Treat Endcap properly.- Improve gamma finding efficiency.- Optimize track matching parameters.
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