t.yoshioka (icepp) , m-c.chang(tohoku), k.fujii (kek),

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


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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.


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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.


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- Tower

- # of Layers ECAL : 38 HCAL : 130

- Side view



40 cm270 cm

210 cm

Full One Tower　 ECAL + HCAL

ECAL

HCAL


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- Cell

- Cell Size EM : 4cm x 4cm HD : 12cm x 12cmCan be changed easily.

- Tower

- # of Layers ECAL : 38 HCAL : 130

- Side view



40 cm270 cm

210 cm

Full One Tower　 ECAL + HCAL

27 X0

6.1λ

ECAL

HCAL


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Energy Deposit in a Cell

ECAL HCAL

- Z → qq-bar(q = u,d,s)@91.187GeV.


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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


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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.


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Small Cluster Distributions

Number of hitsin a small cluster

Small ClusterEnergy

- Z → qq-bar(q = u,d,s)@91.187GeV.


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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


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Thrust and Broadening

Thrust Broadening

- Z → qq-bar(q = u,d,s)@91.187GeV.


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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%.


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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


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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…


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Distance Distribution

ECAL HCAL

- Z → qq-bar(q = u,d,s)@91.187GeV.


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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…


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Event Display

Z → qq-bar

Red : pionYellow : gammaBlue : neutron

e+

e-


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Event Display

At first, charged hadrons in Endcap regionare removed by cheating method.


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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.


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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.

t.yoshioka (icepp) , m-c.chang(tohoku), k.fujii (kek),

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