AA->HH StudyAA->4b analysis & (preliminary) Summary

Shin-ichi Kawada(AdSM, Hiroshima University)

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Outline• Introduction• Previous results• Today’s topic– AA->4b BG analysis– analysis of BG suppression (AA->WW, ZZ, 4b)

• Summary & Next plan

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Introduction• Photon Linear Collider (PLC) has been

proposed as one of the options of ILC.• It is expected that we can observe the Higgs

self-coupling in PLC.• Feasibility study of Higgs pair creation in PLC is

needed.

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About PLC

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Electrons

Backward Compton scattering

ILC : e+ e- collision PLC : gamma-gamma collision

gamma-gamma collision

Reaction in gamma-gamma collision

• Signal : AA->HH->4b• Many backgrounds– AA->WW, ZZ, 4b, etc…

• Analysis of background reduction is necessary.– We assumed that Higgs mass equals to 120GeV in

this study.

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4b = b b-bar b b-bar

Previous result (1)• Main backgrounds– AA->WW (~11.6pb, 1.5*107 events/year)– AA->ZZ (~9.42fb, 1.2*104 events/year)

• Analysis with Neural Network– We can observe Higgs pair creation if we can

develop good b-tagging method and jet clustering.

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BG usual cheatAA->WW 2.69 5.85AA->ZZ 1.61 5.85

Previous result (2)• Other background --- AA->4b– cross-section = 46.6fb (with luminosity & (2-jet

invariant mass) < 15 GeV were cut)– ~ 6*104 events/year– need the detector simulation & analysis

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γ b

b-bar

optimistic eventγ

γ

b

bb-bar

b-bar

pessimistic event

: color stringγ b

b-bar

Topic (1) : AA->4b BG analysis

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at the 21st General Meeting4b(opt) : 1.81σ4b(pes) : 1.47σ

not bad, but not enough

need more effective cuts/NN analysis

• use other useful other parameterscosθ of jet (cosθ of 2-jet)event shape (thrust, sphericity, Y-value, etc...)

• jet pairingjet pair of least χH

2 -> χH2 , cosθ of 2-jet

jet pair of least χA2 -> χA

2 , cosθ of 2-jet

Analysis procedure (1)• MC samples– remained events after W filter & Z filter

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realclustering

signal 4b(opt) 4b(pes)

generate 50000 1000000 1000000

pre-selection 29958 241318 287776

W filter 7713 1083 1936

Z filter 6042 624 1240

cheatclustering

signal(cheat)

4b(opt) 4b(pes)

generate 50000 1000000 1000000

pre-selection 29152 241318 287776

W filter(cheat)

24115 4535 7422

Z filter(cheat)

22987 3077 5743

input these events to NN

Analysis procedure (2)• 17 Input parameters to NN– no relation to χ2 (11 parameters)• visible energy, # of tracks, ycut value of jet clustering,

thrust, sphericity, Y-value, cosθ of jet (4), max|cosθ of jet|

– jet pairing of least χH2 (3 parameters)

• χH2 , cosθ of 2-jet (2)

– jet pairing of least χA2 (3 parameters)

• χA2 , cosθ of 2-jet (2)

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Result

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real clustering signal 4b(opt)remained events 4025 16

significance(evaluated signal & 4b BG only)

1.92σ

real clustering signal 4b(pes)remained events 3128 24 1.43σ

cheat clustering signal(cheat)

4b(opt)

remained events 22173 165.59σ

cheat clustering signal(cheat)

4b(pes)

remained events 21587 175.49σ

Goodsuppression!!

Discussion• Significance (signal v.s. single BG) with cheat

jet clustering is good!– signal (cheat) v.s. WW (cheat) : 5.85σ– signal (cheat) v.s. ZZ (cheat) : 5.85σ– signal (cheat) v.s. 4b (optimistic) : 5.59σ– signal (cheat) v.s. 4b (pessimistic) : 5.49σ

• try to apply the NN analyses to all events!

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Topic (2) : Analysis of BG suppression

• Analysis procedure1. pre-selection2. W filter (1st NN selection)3. 4b filter (2nd NN selection)4. Z filter (3rd NN selection)

• Cross-section : WW > 4b > ZZ

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pre-selection• Lorentz factor β2j > 0.05• |cosθ of 2-jet| < 0.99• nbj >= 3– # of b-flavor jets with nsig=3.0 & noffv=1 analysis

• nbtj >= 2– # of b-flavor jets with nsig=3.0 & noffv=2 analysis

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to suppress huge WW BG

Input parameters to NN• 1st NN selection --- 9 parameters– χH

2 , χZ2 , # of b-flavor jet, etc...

• 2nd NN selection --- 17 parameters– same as page10

• 3rd NN selection --- 10 parameters– χH

2 , χW2 , χZ

2 , etc...

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Details are shown in page24.

Cut Summaryreal clustering & 4b (optimistic)

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HH WW ZZ 4b(opt)expected events(# of MC events)

80(50000)

73100000(75000000)

59350(1000000)

293600(1000000)

pre-selection 47.93(29958)

81655(83777)

5167(87057)

70851(241318)

W filter 12.34(7713)

8.772(9)

193.4(3259)

318.0(1083)

4b (opt) filter 7.262(4539)

1.949(2)

73.89(1245)

7.340(25)

Z filter 4.823(3018)

0.9747(1)

9.377(158)

3.817(13)

significance= 4.823√4.823+0.9747+9.377+3.817

=1.11𝜎PRELIMINARY

Cut Summaryreal clustering & 4b (pessimistic)

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HH WW ZZ 4b(pes)expected events(# of MC events)

80(50000)

73100000(75000000)

59350(1000000)

293600(1000000)

pre-selection 47.93(29958)

81655(83777)

5167(87057)

84491(287776)

W filter 12.34(7713)

8.772(9)

193.4(3259)

568.4(1936)

4b (pes) filter 8.238(5149)

0(0)

84.40(1422)

13.21(45)

Z filter 4.994(3121)

0(0)

7.359(124)

5.872(20)

significance= 4.994√4.994+0+7.359+5.872

=1.17𝜎PRELIMINARY

Cut Summarycheat clustering & 4b (optimistic)

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HH (cheat) WW (cheat) ZZ (cheat) 4b(opt)expected events(# of MC events)

80(50000)

73100000(75000000)

59350(1000000)

293600(1000000)

pre-selection 46.64(29152)

55836(57287)

4172(70292)

70851(241318)

W (cheat) filter 38.58(24115)

4.873(5)

98.94(1667)

1331(4535)

4b (opt) filter 35.56(22223)

3.899(4)

41.78(704)

3.817(13)

Z (cheat) filter 33.26(20787)

1.949(2)

5.045(85)

3.817(13)

significance= 33.26√33.26+1.949+5.045+3.817

=5.01𝜎PRELIMINARY

Cut Summarycheat clustering & 4b (pessimistic)

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HH (cheat) WW (cheat) ZZ (cheat) 4b(pes)expected events(# of MC events)

80(50000)

73100000(75000000)

59350(1000000)

293600(1000000)

pre-selection 46.64(29152)

55836(57287)

4172(70292)

84491(287776)

W (cheat) filter 38.58(24115)

4.873(5)

98.94(1667)

2179(7422)

4b (pes) filter 34.50(21562)

2.924(3)

27.66(466)

2.642(9)

Z (cheat) filter 33.06(20662)

2.924(3)

5.935(100)

2.642(9)

significance= 33.06√33.06+2.924+5.935+2.642

=4.95𝜎PRELIMINARY

(Preliminary) Summary• We can observe the Higgs self-coupling with

~5σ if we use cheat jet clustering.• It is possible to measure the Higgs self-

coupling in PLC if we can develop good jet clustering algorithm.

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Next Plan• Check the statistical fluctuation• Check/Evaluate the NN systematic error– Now : (training file) = (test file)

• Write a paper

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Backup slides

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sphericity, Y-value

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normalized momentum tensor Mab

𝑀 𝑎𝑏=∑𝑖𝑝𝑖𝑎𝑝𝑖𝑏/∑

𝑖𝑝𝑖2

pi : momentum of particle i

3*3 matrix

eigenvalue𝑄1 ,𝑄2 ,𝑄3(𝑄¿¿1≤𝑄2≤𝑄3)¿

sphericity=32 (𝑄1+𝑄2 )

Y −value=√32 (𝑄2−𝑄1 )

Input parameters to NN (details)

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1st --- 9 parametersχH

2 , χZ2 , visible energy, # of tracks, ycut value of jet clustering,

longitudinal momentum, transverse momentum,# of b-flavor jets with nsig = 3.5 & noffv = 1 analysis,# of b-flavor jets with nsig = 3.5 & noffv = 2 analysis

2nd --- 17 parameters

3rd --- 10 parameters

same as page10

χH2 , χW

2 , χZ2 , energy of 2-jet (2), visible energy,

# of tracks, longitudinal momentum# of b-flavor jets with nsig = 3.5 & noffv = 1 analysis,# of b-flavor jets with nsig = 3.5 & noffv = 2 analysis