Post on 31-Mar-2020
Higgs self-coupling projections at ILC
Junping Tian (U. Tokyo)
— on behalf of ILD
Higgs Coupling 2018, Nov. 26-30 @ Tokyo
ILC Supporters
!2
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
10
λhhh: can we really determine it mode independently?
in a general model by SMEFT
σΗΗΧ depends on many other couplings
SM
11
+ 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
!14
backup
Higgs couplings in EFT
15
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
18
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?
!20
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