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Top-quark reconstruction with Fast Simulation

M. Iwasaki University of Oregon


At the Sitges meting: tt 6jets & 4jets analysis
· Charged/Neutral cluster separation with Track-cluster matching · Reconstruction performance in Energy flow analysis · B-tag effect

After the meeting:
· In FastMC, set the cluster position resolution determined by FullMC · Study Cluster width with FullMC · Cluster merging


Energy flow analysis
Tracker Charged hadron, electron Neutral hadron, photon Calorimeter

Charged/Neutral cluster separation See Track-Cluster matching · · · · Cluster position resolution Granularity, shower width Magnetic Field Calorimeter Radius


Cluster position resolution So far, we use = 1cm/E for e, and 5cm/ E for hadrons in FastMC Electron,photon
220 200 120 180 160 140 120 100 80 60 40 20 20 0 0 0 0 40 80 100
DistE_b_egam Nent = 7368 Mean = 2.436 RMS = 2.043

Hadrons
140

DistE_b_pikp Nent = 6967 Mean = 2.872 RMS = 2.591

60

(Small)
2 4 6 8 10

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Distance between McPart and Cluster in FullMC / E

(cm)

(cm)


Cluster position resolution Electron,photon
DistE_b_egam Nent = 6809 Mean = 2.271

Hadrons
DistE_b_pikp Nent = 6311 Mean = 3.489 RMS = 2.055

220 200

80 70

RMS = 2.752

180 160 140 120 40 100 80 60 40 20 0 0 10 0 0 30 20 60 50

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(Large)

Distance between McPart and Cluster in FullMC / E

(cm)

(cm)


Hadrons have very long tail...
DistE_b_pikp Nent = 6967 Mean = 11.46

350

RMS = 14.18

300

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(cm)

e and Set 3cm/E (both in S and L) Hadrons Need another parameterization


Charged/Neutral Cluster separation
Extrapolate Charged tracks to the Cluster radius Then see the Cluster-Track matching distance for the nearest track

Cluster = Track
1000 60 800 50

photon

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(cm)

(cm)


Small
Track = Cluster
dL_t Nent = 3533 Mean = 1.198 RMS = 2.342

Photon
60

dL_g Nent = 4844 Mean = 8.806 RMS = 5.24

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Large
900 800 700 600

dL_t Nent = 3398 Mean = 1.503 RMS = 2.786

dL_g Nent = 4864 Mean = 11.45 RMS = 4.946

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25

20 500 400 300 200 5 100 0 2 4 6 8 10 12 14 16 18 20 0 0 15

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Small Large B= 6T, R = 75cm 3T, 2m Charged cluster rejection 86 % 85 % Neutral cluster efficiency Track-cluster separation .. B*R2 B=3T, R=2m corresponds to B = 6T, R = 1,4m At Sitges .. Charged cluster rejection 96 % 97 % 99 % 95 % 99 %

Neutral cluster efficiency 95 %
· 1cm/E position smearing · Using McPart momentum instead of Track momentum when extrapolate the track (Bug)


Cluster merging effect The fast simulator does not have Cluster width yet Near clusters might be merged and regard as one cluster


Transverse Cluster width at FullMC
200 180 160 140 120 100 80 6 60 4 40 20 0 0 2 0 0 12 10 8

Electron,photon

16 14

Hadrons

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4

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10

(cm)

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4

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(cm)

Distance between McPart and CAL Hit Small 1.3 ± 0.3 cm Large 1.3 ± 0.4 cm 3.2 ± 0.3 cm 3.5 ± 0.4 cm


Cluster merging effect Transverse cluster width Small 2â Moliere radius(EM) 1.5cm(W) e, cluster width 1.3cm Granularity: 20mrad ~1.5cm Large 2.5cm(Pb) 1.3 cm > 4.0cm

Merging probability (transverse only) 13mrad 20mrad 30mrad(JLC) Small 3.2% 6.3% 11.6% Large 6.6% 11.7%


tt 6jets reconstruction
Generator:: PANDORA-PYTHIA(6.1) Includes initial-state radiation + beam spread Ecm = 500GeV, mt = 175GeV Event selection: ·Require # of jets 6jets at ycut = 0.004 with Jade clustering .. then change the ycut and forced to have 6 jets ·W Mass cut m2jets ~ mW ± 12 GeV ·Energy fraction Xjet E3jet/Ebeam 0.95 < Xjet < 1.05 ·Regard top candidate.. m3jets ~ mt ± 10 GeV


tt 6jets reconstruction
W_mass Nent = 24045 Mean = 86.14 RMS = 22.49 Xjet_all Nent = 22140

2000 1800

Mean = 0.8843 RMS = 0.1884

500 1600 400 1400 1200 300 1000 800 200 600 400 200 0 30 40 50 60 70 80 90 100 110 120 0 0

100

0.2 0.4 0.6 0.8

1

1.2 1.4 1.6 1.8

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Mass

2jets

X

3jets

Reconstructed W mass resolution ~8.4 GeV


tt 6jets reconstruction
NJETS_all Nent = 2277 Mean = 5.841 RMS = 0.7139
ycut_6j Nent = 1603 Mean = 0.004322 RMS = 0.0008526

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# of Jets

Ycut which gives 6-jets


tt 6jets reconstruction Small
220 200 180 200 160 140 120 100 80 60 40 20 0 100 120 140 160 180 200 220 240 260 0 100 120 140 160 180 200 220 240 260 50 100 150
T_mass Nent = 3781 Mean = 201.5 RMS = 29.18

Large
250

T_mass Nent = 3996 Mean = 199.2 RMS = 29.29

Mass

3jets

Mass

3jets


tt 6jets reconstruction (with b-tag) Small
90 80 70 60 50 40 40 30 20 10 0 100 0 100 60 80
T_massb Nent = 1125 Mean = 197.8 RMS = 26.67

Large
100

T_massb Nent = 1148 Mean = 196.6 RMS = 26.34

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Mass

3jets

Mass

3jets


Merging size Small # Top candidates Signal Mass (GeV) Angle (mrad) Large # Top candidates Signal Mass (GeV) Angle (mrad)

No-merge 13 mrad 20 mrad 30 mrad 906 924 914 840 572 598 588 542 10.4 ±0.3 10.2 ±0.4 10.1 ±0.3 10.3 ±0.3 57 ± 2 61 ± 3 65 ± 3 69 ± 3 1006 678 9.8 ±0.5 57 ± 3 961 841 663 537 10.0 ±0.3 10.8 ±0.4 59 ± 3 67 ± 3 Small ... need more radius??


Summary
Using Fast Simulator, we study tt 6jets reconstruction · Using FullMC, study the cluster position resolution Need some parameterization for hadrons · Neutral/Charged cluster separation Need to see longitudinal segmentation and calorimeter radius effect · Various FastMC parameter should be determined by FullMC Need more study using FullMC · Need to optimize the top-quark selection cut