Measuring the ratio of 𝐻𝑊𝑊 and 𝐻𝑍𝑍 couplings
through 𝑊 + 𝑊 − 𝐻 production

Gang LiNational Taiwan University

In collaboration with Cheng-Wei Chiang and Xiao-Gang He
arXiv: 1805.01689, JHEP 1808 (2018) 126

Workshop "Beyond the SM"
Oct. 2, 2018

Higgs measurements
SM(-like) Higgs bosonIn 𝜅-framework
or

LHCHXSWG, 1307.1347

JHEP 1608 (2016) 045

care more about
𝜅𝑊 , 𝜅𝑍

𝑆𝑀
𝑆𝑀𝑔𝐻𝑊𝑊 = 𝜅𝑊 𝑔𝐻𝑊𝑊, 𝑔𝐻𝑍𝑍 = 𝜅𝑍 𝑔𝐻𝑍𝑍

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Ratio of HWW and HZZ couplings

JHEP 1608 (2016) 045

The allowed regions by experimental measurements are two-fold3

Ratio of HWW and HZZ couplings
At the tree-level in the SM
Exp:(1)

PDG 2018(2)

Exp: negative region can not be excluded byconsidered signal strength measurements(1) and (2) are not necessarily correlated
For example, in the Georgi-Machacek model,

H. Georgi and M. Machacek,
Nucl. Phys. B262, 463 (1985)

𝜌 = 1 (custodial symmetry),
𝜆𝑊𝑍 =1,-1/24

Ratio of HWW and HZZ couplings
SM + complex triplet + real triplet & custodial symmetry
H. Georgi and M. Machacek, Nucl.
Phys. B262, 463 (1985).

𝜌 = 1, 𝜆𝑊𝑍 =1,-1/2
A realistic model:

J.-Y. Cen, J.-H. Chen, X.-G. He, J.-Y. Su, 1803.05254

SM + complex triplet + real triplet & 𝜌 = 1

𝜆𝑊𝑍 is generally arbitrary
In GM model, tan𝛾 = −√25tree-loop interference

through differential distribution of h-> 4l(1) assumption of the top quark Yukawa coupling(2) more loop diagrams to keep gauge invariance(3) kappa-framework is inconsistent for differential distributions
C. Mariotti, G. Passarino, 1612.00269
6tree-tree interference
𝐻𝑊𝑊 and 𝐻𝑍𝑍 couplings can interfere at the tree-level𝑎𝑎ത → 𝑊 + 𝑊 − 𝐻, 𝑎 = 𝑞, 𝑒 −taking 𝑚𝐻 =125 GeV as an example

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tree-tree interference
At the LHC: SM pp -> W+ W- H can not be discovered (below 2𝜎)

8tree-tree interference
At future electron-positron colliders:√Interference in the SM (𝜆𝑊𝑍 = 1) is negative9

Collider analysis

Conventional approachdo kw=kw_min, kw_max, step_kw
do kz=kz_min, kz_max, step_kz(1) generate p p > W+ W- H, W+ > l+ vl, W- > j j, H > x y(2) impose cuts to suppress backgrounds(3) obtain the significance(4) obtain the sensitivity to the ratio
end doend doShow plot of sensitivity

10Collider analysis
Signal cross section after cuts:

we only need three benchmark scenarios:

cut efficiencies are
independet of the branching ratios

11Collider analysis
Discovery significanceG. Cowan, K. Cranmer, E. Gross, O. Vitells, Eur.Phys.J.
C71 (2011) 1554

Discrimination between 𝜆𝑊𝑍 ≠ 1 and 𝜆𝑊𝑍 = 1ratio test

under the SM hypothesis

𝜆𝑊𝑍 = 𝜆0 is rejected at the 𝑍-sigma level with

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Collider analysis

Higgs decay channel:(1) H -> b b~

𝝀𝑾𝒁 < 𝟎. 𝟒𝟏

𝜿𝑾 > 𝟎. 𝟔

𝜿𝑾 > 𝟎. 𝟗 (other exps.),negative 𝝀𝑾𝒁 exclued

13Collider analysis

Higgs decay channel:(2) H -> W+ W-

scheme A: couplings of H to SM fermions are the same as the SM Higgs boson
scheme B: H does not couple to the SM fermions at the tree-levelmotivated by GM model

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Collider analysis

Higgs decay channel:(2) H -> W+ W-

scheme A

𝜆𝑊𝑍 < 0.46

𝜅𝑊 > 0.9

𝜿𝑾 > 𝟏 (other exps.),negative 𝝀𝑾𝒁 exclued15Collider analysis

Higgs decay channel:(2) H -> W+ W-scheme B

motivated by GM model

16Collider analysis
Improvement of precision measurement, which assumes that 𝜆𝑊𝑍 is close to 1

arXiv: 1307.7135(WWH@500)(HL-LHC)(H -> b b~)(H -> W+ W-)
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Summary• Through W+W−H production, one can measure the ratio 𝜆𝑊𝑍 of HWW andHZZ couplings• The discovery prospect and discrimination ability are studied• Combined with measurements of HWW or HZZ coupling at HL-LHC,
precision of 𝜆𝑊𝑍 can be 6.3%

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Higgs measurements

All 𝜅s are assumed to be positive
ATLAS-CONF-2018-031

HIG-17-031-pas
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Higgs measurements

𝜅𝑡 is involved in the determination of 𝜅𝑊 or 𝜅𝑍

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Collider analysis

Higgs decay channel:(1) H -> b b~

21Collider analysis

Higgs decay channel:(2) H -> W+ W-22