gamma finding procedure for realistic pfa
DESCRIPTION
Gamma Finding procedure for Realistic PFA. T.Fujikawa(Tohoku Univ.), M-C. Chang(Tohoku Univ.), K.Fujii(KEK), A.Miyamoto(KEK), S.Yamashita(ICEPP), T.Yoshioka(ICEPP) On behalf of ACFA-SIM-J Group. Motivation. - PowerPoint PPT PresentationTRANSCRIPT
13 July 2005 ACFA8
Gamma Finding procedurefor Realistic PFA
T.Fujikawa(Tohoku Univ.), M-C. Chang(Tohoku Univ.), K.Fujii(KEK), A.Miyamoto(KEK), S.Yamashita(ICEPP), T.Yoshioka(ICEPP)
On behalf of ACFA-SIM-J Group
13 July 2005 ACFA8
Motivation
To get high energy resolution in multi jet event, we use the tracker information for charged particles and calorimeter hit information for neutral particles. (tracker resolution is much better than calorimeter’s.)
Particle Flow Algorithm (PFA) is studied to achieve an event reconstruction. We studied part of PFA, “gamma finding method” for GLD detector, using full simulator (Jupiter).
13 July 2005 ACFA8
1.Small Clustering (collect fired cells with its neighbors) → Define thrust and broadening for each small cluster.2. Gamma Finding (Separate gamma/e from 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
Clustering flow for GLD detector
13 July 2005 ACFA8
Detector configuration
40 cm270 cm
210 cm
Full One Tower EM + HD
27 X0
6.1λ
Y.Yamaguchi (Tsukuba Univ.)
In current Jupiter geometry, calorimeter has 4cmx4cm/12cmx12cm scintillator tile size in ECAL/HCAL as a default setting. We used this configuration in our study.
13 July 2005 ACFA8
Why good gamma finding is necessary?
Expected jet-event in the future ILC, it has about 20% gamma contribution.
Also, if we can separate gamma (and also electron) well, it make the charged hadron clustering easier.
good gamma/charged hadron separation is necessary!
(Z->qqbar @ Ecm = 91.2 GeV)
K
n pLK
13 July 2005 ACFA8
Flow of the gamma finding
As a first step of the clustering, we collect hit cells with its neighbors (with ~50MeV energy deposit upper limit). We call it “small cluster”. Our gamma finding method is performed based on the small clusters.
1. Find “large” small cluster within ECAL region (we call it “mother small cluster”).
2. Apply “Gamma-Fitter” chi-square /ndf cut. (cut 1)
3. Apply “the distance from the nearest track” cut for mother small cluster. (cut 2)
4. Collect small clusters within a tube.
The flow of Gamma Finding
13 July 2005 ACFA8
Gamma finding method
1. Gamma Fitter (chi-square cut of fit)Find large small cluster within ECAL region and make a small tube along its thrust axis.
Take an average of energy deposit for each 3-layers within a tube and fit the total energy deposit by Gamma distribution function.
The result of chi-square/ndf is used to separate gamma/electron from hadrons.
13 July 2005 ACFA8
Energy deposit in three layersare merged to reduce fluctuation.
Choose large small cluster (mother small cluster) within ECAL region and make a small tube (R = 5cm) along to its thrust axis.
Fit the longitudinal shower profile of the energy deposition within a tube as an electromagnetic cascade (gamma distribution function).
Gamma Fitter: algorithm
HCAL projection axis
take an average energy deposit for each 3-layers
mother small cluster
ECAL
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Gamma Fitter: single particle test
5.0,/ where
)(
)exp()(0
Functionon Distributi Gamma
0
1
bXxt
a
btbtbE
dt
dE a
The result of fitting for a single particle case (gamma at 3GeV)
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3 GeV
10 GeV5 GeV
1 GeV Yellow: gamma
Red : pion
We can separate gamma/electron from pion using chi2/ndf cut.
Comparison of chi2/ndf (single particle)
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Blue : efficiency
Red : purity
Gamma Fitter: efficiency and purity
(Z->qqbar @ Ecm = 91.2 GeV)
The “Gamma fitter” works good for z->qqbar event, too. But it doesn’t have high efficiency for electron/gamma finding. (maximum ~ 90%)
13 July 2005 ACFA8
Chi2/ndf (Z->qqbar @ Ecm = 91.2 GeV)
Yellow: e/gamma
Red : all particles
cut position
We set a cut position at 1.0 for below gamma finding.
(~70% efficiency and ~70% purity)
13 July 2005 ACFA8
2. The distance from the nearest track
Calculate the distance between mother small cluster and its nearest track. The distance is used to separate gamma from charged particles.
Gamma finding method
HCAL
ECAL
gamma
track
distance
mother small cluster
13 July 2005 ACFA8
Distance from the nearest track
Blue : electron
Red : all particles
Yellow: Gamma
(Z->qqbar @ Ecm = 91.2 GeV)
This plot shows the distribution of the distance from the nearest track for all small clusters within ECAL region. (energy-weighted)
13 July 2005 ACFA8
Distance distribution (Z->qqbar @ Ecm = 91.2 GeV)
Blue : electron
Red : all particles
Yellow: Gamma
After Chi2/ndf < 1.0 cut
cut position
We set a lower limit at 13cm. It kills the electron as well, but can reduce large amount of charged hadron contamination. We gain the benefit anyway.
13 July 2005 ACFA8
The result of Gamma finding
1. efficiency
Finally, we got
efficiency ~ 60%
using “gamma fitter cut” and “the distance cut”.
13 July 2005 ACFA8
The result of Gamma finding
2. purity
w/o n,KL contamination
Purity ~ 93%
Purity ~ 99%
contamination is almost caused by n/KL
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The result of energy sum
E/%3.41~ E/%5.34~
Realistic gamma finder Cheated gamma finder
cheated etc.) (neutrinoenergy missing%,2.82~ ,%4.86 :matchingtrack purity
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Other idea (not used now)
1. Energy deposit comparison between ECAL/HCAL regionAssume a tube region and compare the total energy deposit between ECAL/HCAL region within a tube.
ECAL
HCAL
E1
E2
separate events using E1/E2
13 July 2005 ACFA8
2. Energy waited Broadening/Thrust ratio of the clusterCalculate thrust and broadening for the cluster, then calculate these ratio. (EM shower has lower value compare to HD shower’s.)
Other idea (not used now)
ECAL
HCAL
In general, (B/T)EM > (B/T)HD
cluster
cluster
13 July 2005 ACFA8
3. Calculate energy deposition ratio within a tube in ECALSet the tube and “Maximum layer” according to cluster energy, then calculate the energy ratio between upper/lower region of Maximum layer within a tube (region 1 and 2).
Other idea (not used now)
All of them are not effective “after” gamma fitter cut…
ECAL
region 1
region 2
region 1
region 2
gamma hadron
Maximum layer (energy
dependent)
Tube radius is also energy dependent
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Summary
Good gamma finding (clustering) method is necessary for future LC experiment.
We got ~60% efficiency and ~99% purity using Gamma Fitter (chi2/ndf) + the nearest track distance requirement.
Current gamma finding method has high purity but which doesn’t have enough efficiency.
13 July 2005 ACFA8
Next step
Combine other gamma finding method (or study another method other than “gamma fitter”) to get high efficiency/purity.
Do the cut value optimization.
Study other method which use transverse shower profile.
Study the “relationship” with clustering method for charged hadron.
13 July 2005 ACFA8
The result of other gamma finding method with gamma fitter chi-square cut
Backup
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HCAL/ECAL e-dep comparison
After Chisquare/ndf < 1.0 cut
Yellow: e/gamma
Red : all particles
The plot shows the energy deposit comparison between HCAL/ECAL regions after applying the chi-square cut for Z->qqbar event.
13 July 2005 ACFA8
Broadening/Thrust
Yellow: e/gamma
Red : all particlesAfter Chisquare/ndf < 1.0 cut
Broadening/Thrust ratio for the cluster after applying the chi-square cut for Z->qqbar event.