Probing the interaction of the Higgs boson and the top-quark to explore the origin of the masses of elementary particles.

S.Cabrera Urbán on behalf of the ATLAS Collaboration

Instituto de Física Corpuscular (IFIC) - CSIC/UV

Probing the interaction of the Higgs boson and the top-quark

to explore the origin of the

masses of elementary particles.

• Circular accelerator: 26.7 km.

• pp collisions , also heavy-ion collisions: Pb+Pb,p+Pb,Xe+Xe

• Superconducting magnets. Target beam energy: 7TeV.

• 8 Interaction regions: 4 particle physics experiments: ATLAS, CMS, ALICE and LHCB.

• Run-1:

• 2011 (E_beam=3.5 TeV ) -2012 ( E_beam=4 TeV )

• 50 ns bunch spacing. L_int = 30 fb-1

• LS1: to consolidate magnet interconnections.

• Run-2: 2015-2018

• E_beam = 6.5 TeV

• 25 ns bunch spacing. L_int = 160 fb-1

• LS2: 2019-2020

• Run-3 prospects:

• Target E_beam = 7 TeV

• 2022: commissioning year with 10-20 fb^-1

• 2023/2024: production year with 80 fb^-1 per year. Luminosity levelled at <μ>≈55, 80%

The Large Hadron Collider LHC: RUN-2 and TOWARDS RUN-3

THE FULL RUN-2 DATASET & THE ATLAS EXPERIMENT.

• ATLAS detector:

• Muon spectrometer.

• Calorimeters: electromagnétic and hadronic.

• Inner detector: main tracking system.

• Magnetic system: 2T

• Trigger system:

• 2 levels: hardware and software based.

• Excellent detector performance.

• Data taking efficiency = 94%

• Data quality fraction = 95.6%

• Precision object performance.

• Energy scale for central jets ~1% for p_T ~ 250- 2000 GeV

ATLAS Experiment © 2008 CERN

ATLAS-CONF-2019-021.

L_int=139 fb-1, 1.7% uncertainty

Eur. Phys. J. C 81 (2021) 689

The Top-Higgs Yukawa coupling.

• Why should we measure the Top-Quark-Higgs-boson Yukawa Coupling (y_t) ?

• In the SM the Higgs field couples to fermions through a Yukawa interaction and the coupling strength is proportional to the mass of the fermion.

• y_t is the strongest coupling of the Standard Model, almost unity.

• Fermionic decay modes provide direct measurement of the Yukawa couplings at LHC.

• y_t is the only Higgs coupling that can not be measured from direct Higgs decay.

• ☞ We need to measure associated production of Higgs bosons and Top quarks.

• The running of the Higgs-boson-self coupling constant (y) is sensitive to y_t

• Implications in the EW vacuum stability.

Bezrukov and Shaposhnikov,

J.Exp.Theor.Phys. 120 (2015) 3, 335-343;

Top-Higgs Yukawa Coupling from associated production ttH and tH

• Both ttH and tH are challenging processes to explore at the LHC:

• Small cross sections: ≈ 500 fb (ttH, NLO) and 74 fb (tH,5FS) arXiv:1610.07922

• Large variety of final states: combine top pair (single top) and Higgs boson decay signatures.

• The tHq process is sensitive to the magnitude and also to the sign of the Top-Higgs Yukawa coupling y_t ( destructive interference in the SM between Higgs radiation from Top quarks or W bosons )

• Their observations allow probing the CP properties of the y_t coupling.

CMS-PAS-HIG-19-008

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ttH production: STATUS.

• Both ATLAS and CMS experiments reported two independent observations of the ttH production.

• ATLAS: 80 fb-1, √s= 13 TeV Phys. Lett. B 784 (2018) 173

• CMS: 5.1, 19.7, and 35.9 fb−1, √s= 7, 8, and 13 TeV, Phys. Rev. Lett. 120 (2018) 231801

• Higgs boson decays defines 3 family of signatures.

ATLAS Lint

(fb

) CMS Lint

(fb

) b+2!(H→!!)

061802

ATLAS-CONF-2020-026 139 Phys. Rev. Lett. 125 (2020) 061801

CMS-PAS-HIG-19-015 137

Multi b (H→bb)

ATLAS-CONF-2020-058 139 CMS-PAS-HIG-18-030

CMS-PAS-HIG-17-026 41.5 35.9

b+leptons

(H→WW*,ZZ*,"") 4 leptons à

ATLAS-CONF-2019-045 Eur. Phys. J. C 80 (2020) 957

80 139

Eur. Phys. J. C 81 (2021) 378

CMS-PAS-HIG-21-006 137

https://twiki.cern.ch/twiki/bin/view/AtlasPublic/HiggsPublicResults

https://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResultsHIG

ttH: Multi b (H→bb). L

= 139 fb

arXiv:2111.06712

• Signal modelled with Powheg Box

• H. B. Hartanto et al.

• Phys. Rev. D 91 (2015) 094003

• 3 signal regions:

• Dilepton and single-lepton resolved and single-lepton boosted

• Dominant background: tt+≥1b

• Modelled with Powheg Box Res

• T. Ježo et al.

• Eur. Phys. J. C 78 (2018) 502

• MVA techniques:

• DNN to find boosted Higgs boson candidate (Keras/TensorFlow)

• Reconstruction BDTs (TMVA )

• Classifications BDTs (TMVA )

ttH: : Multi b (H→bb). L

= 139 fb

• Systematic uncertainties are dominant: modelling of the dominant background tt+≥1b.

• Results compatible with Standard Model within uncertainties.

ATLAS (leptonic, 139 fb

)

arXiv:2111.06712

CMS ( dilepton, single-lepton, fully hadronic) 35.9 fb

( 2016 ) + 41.5 fb

( 2017 )

CMS-PAS-HIG-18-030 Signal strength 0.35 +0.36/-0.34 1.15 +0.32/-0.29

Significance 1.0! (2.7! expected) 3.9! ( 3.5! expected)

STXS FRAMEWORK D. de Florian et al. arXiv:1610.07922

arXiv:2111.06712

ttH: b+2!(H→!!): L

= 139 fb

• Two signal regions:

• targeting lep/had Top quark decays.

• ML techniques: BDT XGBOOST arXiv:1603.02754

• BDT for top quark reconstruction.

• BDT for background rejection discrimination.

• BDT to separate CP-even and CP-odd hypothesis.

• Data driven approach for background estimations.

• !!.+jets / tt+!!

• Simultaneous fit to the m!! spectra.

• EFT definition: Higgs characterization model

• F.Demartin et al, Eur. Phys. J.C 74, 3065 (2014)

• "=90(180)º ( pure CP-odd coupling ) excluded at 3.9# ( 2.5 )#

• CMS: "=90 excluded at 3.2# Phys. Rev. Lett. 125 (2020) 061801

PRL 125 (2020) 061802

ttH: H→!! L

= 139 fb

ATLAS (H→!! , 139 fb

)

ATLAS-CONF-2020-026

CMS (H→!! , 137 fb

)

Phys. Rev. Lett. 125 (2020) 061801

Signal strength

Significance

PRL 125 (2020) 061802 ATLAS-CONF-2020-026

ttH Multileptons: b+leptons (H→WW*,ZZ*,!!) L

= 80 fb

Six final states, defined by the number and flavor of charged-lepton candidates:

ATLAS (80 fb^-1)

ATLAS-CONF-2019-045

CMS (137 fb^-1)

Eur. Phys. J. C 81 (2021) 378

Signal strength 0.58 +0.36/-0.33 0.92 ± 0.19 (stat) +0.17/-0.13 (syst) Significance 1.8" (3.1" expected) 4.7" ( 5.2" expected)

CMS-PAS-HIG-21-006

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tH production: MOTIVATION & STATUS.

• tHq production sensitive to a non-conserving CP Higgs boson coupling to the Top quark.

• F. Demartin et al. Eur.Phys.J.C 75 (2015) 6, 267

• SM: y_t = 1, !_SM(tH) ≈ 74 fb

• Inverted coupling: y_t = -1, !(tH) ≈ 10 ∗!_SM(tH)

• ”tH: Great probe of new physics”

• CMS: only direct search for tH ( 36 fb⁻¹)

• For a standard model–like value of g_HVV: the data favor positive values of y_t by 1.5!

• $_%&'(^)* < 12. Phys. Rev. D 99 (2019) 092005

• CMS: ttH+tH multilepton analysis ( 137 fb⁻¹)

• +_,-./⁰¹ = 3. 5_67.8^97.: Eur. Phys. J. C 81 (2021) 378

• Observed (expected) significance of 1.4 (0.3)!

• ;₎= =₎⁄=₎^>?: -0.9<;_t<-0.7 or 0.7< ;_t <1.1 @95%CL

• Ongoing ATLAS dedicated analysis with full Run-2 dataset:

• Aiming for an upper limit on tH combined cross section and individual analyses, for : y_t = y_t,SM and : y_t = -y_t,SM

CONCLUSIONS AND IFIC PARTICIPATION.

• ATLAS and CMS experiments are deeply exploring the the Top-Higgs-Yukawa coupling y_{t .} through an exhaustive study of the associated production of Higgs bosons with Top quarks.

• The ttH production is measured in a large variety of signatures and final states.

• The most sensitive measurement of ttH production rate to date by CMS with full Run-2 dataset with a significance of 4.7! ( 5.2! expected) with multilepton signatutes (b + multileptons, H→WW*,ZZ*,"" ) Eur. Phys. J. C 81 (2021) 378

• Closely followed by the ATLAS measurement in the Hà## channel with a significance of 4.7! (5.0! expected). ATLAS-CONF-2020-026

• Strong involvement in the IFIC: M. Moreno-Llácer, is leading the analysis group in ATLAS dedicated to explore associated productions of Higgs bosons and top quarks, besides particular involvement in:

• ttH(ML) (80 fb-1) ATLAS-CONF-2019-045

• ttH(##)-CP (Phys. Rev. Lett. 125 (2020) 061802)

• Ongoing in ttH(bb) CP with full Run-2 dataset.

• The tH production remains unobserved.

• Upper limits to σ(tH) from CMS with 36,137 fb⁻¹

• Strong involvement in the IFIC in multilepton analyses with full Run-2 datasets.

• C. Escobar-Ibañez ( Analysis Contact ), P. Martínez-Agulló, J. Guerrero-Rojas, F.

Cardillo and S. Cabrera.

BACKUP

ttH Multileptons: 4 lep: e/! (H→ZZ*). L

= 139 fb

• Two signal regions: 115 GeV < m_4" < 130 GeV

• ttH-Lep-enriched (dileptonic and semileptonic W decays from top pair quark decays )

• ttH-Had-enriched ( fully hadronic top pair decays )

• ML techniques:

• A feed-forward multilayer perceptron MLP ( full event variables )

• Two recurrent RNN for leptons and jets.

• MLP, jet RNN and lepton RNN are combine into an MLP NN discriminant.

• ttH:

• (#∗ℬ)/(#∗ℬ)_SM = 1.7 +1.7/-1.2(stat) ±0.2(exp.)±0.2(th.)

• Constraints on the tensor coupling structure of the Higgs boson in the EFT approach:

• C_uH: [-18,30] ([-14,26]) 95% CL observed (expected)

Eur. Phys. J. C 80 (2020) 957

Event display of a tt̄H(bb̄) candidate event in the single lepton boosted

channel.