Higgs self-coupling projections at ILC

Junping Tian (U. Tokyo)

— on behalf of ILD

Higgs Coupling 2018, Nov. 26-30 @ Tokyo

ILC Supporters

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Sumino, et al, 1503.02819Kanemura, et al, 1508.03245

Motivation to measure the Higgs self-couplings

V (�H) =1

2m2

H�2H + ⇥v�3H +1

4⇥�4H

๏ direct probe of the Higgs potential—> decisive test of the Standard Model

๏ the structure of vacuum is crucial for Baryogenesis models: strongly 1st order phase transition, δλHHH > 20%

EWSB models with classical scale invariance, possibly only self-couplings are deviated: δλHHH ~ 70%

Grojean, et al., hep-ph/0407019 Senaha, et al., hep-ph/0411354

talk by E.Senaha

Higgs self-coupling measurement @ ILC

Center of Mass Energy / GeV400 600 800 1000 1200 1400

Cro

ss S

ectio

n / f

b

0

0.1

0.2

0.3

0.4

0.5

0.6 ZHH→ - + e+e

HH (WW-fusion)νν → - + e+eHH (Combined)νν → - + e+e

) = (-0.8,+0.3)+,e-M(H) = 125 GeV P(e

H

HH

ν

ν−e+

e−

Z

H

ZH

He+

e−

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• √s~500 GeV: e+e- —> ZHH

• √s~1 TeV: e+e- —> νeνeHH

J. Tian, LC-REP-2013-003M. Kurata, LC-REP-2014-025C.Duerig, DESY-Thesis-2016-027

full simulation studies @ ILC

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• dominant channels covered

(for e+e- ->ννHH@1TeV: HH->bbbb/bbWW* are covered)

full simulation studies @ ILC

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• generator: Whizard 1.95, Physsim (realistic beamsstrahlung, ISR, pile-up)

• parton shower & hadronization: Pythia 6

• detector model: ILD (as realistic as possible material budget, blind areas)

• simulation & reconstruction: Geant 4, iLCSoft (realistic algorithms for tracking, particle flow, flavor tagging, jet-clustering, etc)

• event selection: full SM background, realistic cuts, careful categorization, kinematic fitting, multivariate method

full simulation studies @ ILC

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• results (example individual channels)

• results (combined)

Δσ/σ ΔλHHH /λHHH

ZHH @ 500 GeV 4 ab-1 (*) 17% 27%

ννHH @ 1 TeV 4 ab-1 (**) 15% 10%

sZ

Ldt

eff.59%55%19%29%15%

major bkg.: tt, ZZ, ZZZ, ZZH

P(e+, e-) = *: equally shared by (-0.8,+0.3) and (+0.8,-0.3); **: (-0.8,+0.2)

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H

Hν

ν−e+

e−

+

H

Hν

ν−e+

e−

+H

Hν

ν−e+

e−

H

HH

ν

ν−e+

e−

Signal diagram

Z

H

ZH

e+

e−

Z

H

ZH

e+

e−+

+

Z

H

ZH

e+

e−

Z

H

ZH

He+

e−

Signal diagram

� = S�2 + I�+B

(signal diagram)(interference)

(background diagram)

from di-Higgs cross section to λHHH

interference: constructive in ZHH, destructive in ννHH

TeSM

BSM @ 500GeVBSM @ 1TeV

SMλ / λ0.5 1 1.5 2

[%]

λ / λδ

10

210

ZHH @ 500 GeV→-+e+e

HH @ 1 TeVνν→-+e+e

Higgs self-coupling: when λHHH ≠ λSM?

• λΗΗΗ can be enhanced significantly in BSM

• complementarity between ZHH & ννHH (& LHC): interference nature

• if λΗΗΗ / λSM = 2, λΗΗΗ be measured to ~13% using ZHH at 500 GeV e+e-

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Higgs self-coupling: impact of ECM

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[GeV]s500 1000 1500 2000 2500 3000

[%]

λ / λδ

1

10

210HH (100% Eff., no Bkg.)νν→-+e+e

HH (full simulation)νν→-+e+e

ZHH ννHH

[GeV]s500 1000 1500 2000 2500 3000

[%]

λ / λδ

10

210

ZHH (100% Eff., no Bkg.)→-+e+e

ZHH (full simulation)→-+e+e

optimal √s~500-600 GeV preferred √s >=1 TeV

large room for improving full simulation results in future

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λhhh: can we really determine it mode independently?

in a general model by SMEFT

σΗΗΧ depends on many other couplings

SM

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+ 4 SM parameters: g, g’, v, λ10 operators (h,W,Z,γ): cH, cT, c6, cWW, cWB, cBB, c3W, cHL, c’HL, cHE

+ 5 operators modifying h couplings to b, c, τ, μ, g+ 2 parameters for h->invisible and exotic+ 2 operators for contact interactions with quarks

SM Effective Field Theory: full formalism (23 pars.)(“Warsaw” basis)

arXiv:1708.09079; arXiv:1708.08912

12

(statistical error)(systematic error)

λhhh: can we really determine it mode independently? yes!

��hhh

�SM= �c6

Barklow, et al arXiv:1708.09079

all parameters determined simultaneously: EWPOs + TGCs + Higgs @ HL-LHC & ILC

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summary

๏ triple Higgs self-coupling can be determined model independently at e+e-

๏ projections at ILC in SM: 27% by ZHH@500GeV; 10% by ννHH@1TeV; based on full simulation, large room for improvement in future

๏ two channels are very complementary in BSM: ZHH can play a special role in particular when λhhh is largely enhanced

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backup

Higgs couplings in EFT

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Higgs self-coupling: impact of ECM

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[GeV]s500 1000 1500 2000 2500 3000

cros

s se

ctio

n [fb

]-4

-2

0

2

4 HH)νν→-+e+(e0σSσ

Bσ

Iσ

M(H) = 125 GeV) = (-0.8,+0.2)+,e-P(e

[GeV]s500 1000 1500 2000 2500 3000

cros

s se

ctio

n [fb

]

0

0.05

0.1

0.15

0.2

0.25

0.3ZHH)→-+e+(e0σ

Sσ

Bσ

Iσ

M(H) = 125 GeV) = (-0.8,+0.3)+,e-P(e

� = S�2 + I�+B

ZHH ννHH

Higgs self-coupling: impact of ECM

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[GeV]s500 1000 1500 2000 2500 3000

sens

itivi

ty fa

ctor

0

2

4

6

8ZHH→-+e+eHHνν→-+e+e

��

�= F · ��

�F =

�

2S�2 + I�sensitivity factor

[GeV]s500 1000 1500 2000 2500 3000

sens

itivi

ty fa

ctor

(rel

ativ

e)

0

0.5

1

1.5

2

2.5

3ZHH→-+e+eHHνν→-+e+e

|F| |F| (relative to 1 TeV)

hhVV, hVV and λhhh in e+e- —> Zhh

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Z⇤

h

e�

e+

h

h

Z

Z⇤

e�

e+

h

h

Z

Z⇤

e�

e+

h

h

Z

Z⇤

e�

e+

h

h

Z

M(HH) [GeV]200 250 300 350 400 450 500

/dM

(HH

) [fb

]σd

0

0.5

1

1.5-310×

AllS-termQ-termB-termSQ-termSB-termQB-term

[%]HHVVκδ-110 1 10 210

[%]

HH

Hκδ

0

50

100

150

(S) (Q) (B) (B)

δκhhVV < 5% would be needed —> challenging by shape

Higgs self-coupling: indirect determination

McCullough, arXiv:1312.3322

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• if only δh is deviated —> δh ~ 28%

• if both δz and δh deviated —> δh ~ 90%

• δσ could receive contributions from many other sources—> δh ~ 500% at 250GeV only; Gu, Liu, et al, arXiv:1711.03978

• what if we also include other NLO effects as well?

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M(H1) / GeV50 100 150 200

M(H

2) /

GeV

50

100

150

200vvHH no cheat

vvZH no cheat

vvbbbb no cheat

M(H1) / GeV50 100 150 200

M(H

2) /

GeV

50

100

150

200vvHH cheated

vvZH cheated

vvbbbb cheated

real jet-clustering

ννHH mode: (BG: ZZH and ZZZ)

perfect jet-clustering

scatter plot of two Higgs masses

✦ the mis-clustering of particles degrades significantly the separation between signal and BG.

✦ it is studied that using perfect color-singlet-jet-clustering can improve δλ/λ by 40%!

impact of jet-clustering algorithm