Higgs Boson Decays to Light Scalars at ATLAS University of - PowerPoint PPT Presentation

Higgs Boson Decays to Light Scalars at ATLAS University of Birmingham, 22 nd April 2020 Elliot Reynolds Jet a h 125 ℓ + Z ℓ − This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme under grant agreement no 714893 (ExclusiveHiggs)

Ways to Extend the Higgs Sector

Standard Model Higgs Sector Higgs Doublet field introduces gauge invariant mass terms to the Standard Model (SM), facilitates electroweak (EW) symmetry breaking (EWSB), and preserves the unitarity of W L W L → W L W L � � 0 1 φ = √ 2 v + h ( x ) � φ 1 ( x ) + i φ 2 ( x ) � 1 → m W = 1 φ = 2 g W v √ 2 φ 3 ( x ) + i φ 4 ( x ) � m Z = 1 g 2 W + g ′ 2 2 v Elliot Reynolds Higgs Decays To Light Scalars 1 / 34

Observed Higgs Boson arXiv:1307.1347 Elliot Reynolds Higgs Decays To Light Scalars 2 / 34

Observed Higgs Boson Single neutral Higgs boson ( h 125 ) with a mass of 125 GeV discovered in 2012 by ATLAS and CMS arXiv:1307.1347 ATLAS-CONF-2018-031 Elliot Reynolds Higgs Decays To Light Scalars 2 / 34

Extended Higgs Sectors The SM is not the only possible Higgs sector, just the simplest Elliot Reynolds Higgs Decays To Light Scalars 3 / 34

Extended Higgs Sectors The SM is not the only possible Higgs sector, just the simplest More motivations: Supersymmetry, CP-violation, dark matter... Elliot Reynolds Higgs Decays To Light Scalars 3 / 34

Extended Higgs Sectors The SM is not the only possible Higgs sector, just the simplest More motivations: Supersymmetry, CP-violation, dark matter... EW precision measurements impose: Z cos 2 θ W ) = 1 . 00039 ± 0 . 00019 ρ ≡ m 2 W / ( m 2 Naturally achieved by configuration of scalar singlets and doublets Elliot Reynolds Higgs Decays To Light Scalars 3 / 34

Extended Higgs Sectors The SM is not the only possible Higgs sector, just the simplest More motivations: Supersymmetry, CP-violation, dark matter... EW precision measurements impose: Z cos 2 θ W ) = 1 . 00039 ± 0 . 00019 ρ ≡ m 2 W / ( m 2 Naturally achieved by configuration of scalar singlets and doublets Simplest extensions to the SM Higgs sector: Higgs doublet with one or more additional scalar singlets Two Higgs doublet model (2HDM) 2HDM with an additional singlet (2HDM+S) Elliot Reynolds Higgs Decays To Light Scalars 3 / 34

Extended Higgs Sectors The SM is not the only possible Higgs sector, just the simplest More motivations: Supersymmetry, CP-violation, dark matter... EW precision measurements impose: Z cos 2 θ W ) = 1 . 00039 ± 0 . 00019 ρ ≡ m 2 W / ( m 2 Naturally achieved by configuration of scalar singlets and doublets Simplest extensions to the SM Higgs sector: Higgs doublet with one or more additional scalar singlets Two Higgs doublet model (2HDM) 2HDM with an additional singlet (2HDM+S) More complex scalar sectors (including involving triplets) are possible, leading to exotic signatures such as doubly charged Higgs bosons Elliot Reynolds Higgs Decays To Light Scalars 3 / 34

Two Higgs Doublet Model The 2HDM has a pair of scalar doublet fields Elliot Reynolds Higgs Decays To Light Scalars 4 / 34

Two Higgs Doublet Model The 2HDM has a pair of scalar doublet fields Physical Higgs bosons: h and H (CP-even), a (CP-odd), and H ± Elliot Reynolds Higgs Decays To Light Scalars 4 / 34

Two Higgs Doublet Model The 2HDM has a pair of scalar doublet fields Physical Higgs bosons: h and H (CP-even), a (CP-odd), and H ± tan β = v 2 / v 1 Elliot Reynolds Higgs Decays To Light Scalars 4 / 34

Two Higgs Doublet Model The 2HDM has a pair of scalar doublet fields Physical Higgs bosons: h and H (CP-even), a (CP-odd), and H ± tan β = v 2 / v 1 To avoid tree-level flavour changing neutral currents, all fermions of a given charge and quantum numbers couple to one doublet ( arXiv:1207.1083 ) 2HDM Type First Doublet Second Doublet Type-I All fermions Type-II (Supersymmetry) Up-type fermions Down-type fermions Type-III Quarks Leptons Type-IV Up-type quarks Down-type quarks Down-type leptons Up-type leptons Elliot Reynolds Higgs Decays To Light Scalars 4 / 34

Two Higgs Doublet Model with an Additional Singlet The 2HDM+S extends the 2HDM by one singlet field This extends the scalar sector of the 2HDM by one neutral CP-even boson and one neutral CP-odd boson The Type-II 2HDM+S is featured in Supersymmetric models, where it solves a naturalness problem in the Higgs mass scale The 2HDM+S is less constrained that the 2HDM tan Β� 0.5, TYPE II tan Β� 5, TYPE II 1 1 bb bb cc cc ss ss ΤΤ ΤΤ ΜΜ ΜΜ gg gg 0.1 0.1 Br � a � SM � Br � a � SM � arXiv:1312.4992 0.01 0.01 0.001 0.001 uu uu dd dd ΓΓ ΓΓ 10 � 4 10 � 4 1 2 5 10 20 50 1 2 5 10 20 50 m a � GeV � m a � GeV � Elliot Reynolds Higgs Decays To Light Scalars 5 / 34

Heavy or Light? The new scalars can be heavy... Many active search channels: H → ττ ( arXiv:2002.12223 ) H → µµ ( arXiv:1901.08144 ) H → WW ( arXiv:1710.01123 ) H → γγ ( arXiv:1707.04147 ) bH → bbb ( arXiv:1907.02749 ) H ± → tb ( arXiv:1808.03599 ) H ± → τν ( arXiv:1807.07915 ) H ± → ZW ( arXiv:1806.01532 ) H ±± → W ± W ± ( arXiv:1808.01899 ) They could be too heavy to be produced at the LHC Elliot Reynolds Higgs Decays To Light Scalars 6 / 34

Heavy or Light? The new scalars can be heavy... Or they can be light Many active search channels: Previous experiments would not H → ττ ( arXiv:2002.12223 ) have discovered them if their H → µµ ( arXiv:1901.08144 ) only large coupling is to h 125 H → WW ( arXiv:1710.01123 ) H → γγ ( arXiv:1707.04147 ) h 125 → aa and h 125 → Za bH → bbb ( arXiv:1907.02749 ) possible H ± → tb ( arXiv:1808.03599 ) H ± → τν ( arXiv:1807.07915 ) Subject of what follows H ± → ZW ( arXiv:1806.01532 ) (specifically: m < 4 GeV) H ±± → W ± W ± Small natural width of h 125 ( arXiv:1808.01899 ) means even small couplings to new light resonances would lead They could be too heavy to be to large BRs produced at the LHC Elliot Reynolds Higgs Decays To Light Scalars 6 / 34

Heavy or Light? Γ h 125 ≈ 4 . 07 MeV Γ h 125 / m h 125 ≈ 3 . 3 × 10 − 5 H → bb , ττ suppressed by y b , τ < O (10 − 2 ) H → γγ , gg , Z γ suppressed by loop factors Small natural width of h 125 means even small couplings to H → WW ∗ , ZZ ∗ , t ¯ t suppressed by new light resonances would lead phase space to large BRs Elliot Reynolds Higgs Decays To Light Scalars 6 / 34

Current ATLAS Search Programme (Selection of Searches)

ATLAS Detector LHC: 13 TeV pp collisions Run 2: L int = 139 fb − 1 to date Hadrons Photons Electrons+Muons Neutrinos arXiv:1011.6665 Elliot Reynolds Higgs Decays To Light Scalars 7 / 34

ATLAS 2HDM+S H → aa Summary Plots HDBS-2018-46 Type-II Type-IV Type-III 8 10 8 aa) 7 aa) 10 aa) 10 10 7 → 6 10 → 10 7 → B(H 6 10 B(H B(H 10 5 6 5 10 10 × × 4 × H SM 10 SM SM H 5 tan β = 0 . 5 σ 10 4 H 10 σ σ σ σ 3 σ 95% CL on 10 95% CL on 95% CL on 10 3 4 10 10 2 2 10 3 10 10 10 1 2 1 10 ATLAS Preliminary − − 10 1 1 10 10 Run 1 : s = 8 TeV, 20.3 fb -1 − − 2 2 10 10 -1 1 Run 2 : s = 13 TeV, 36.1 fb − − 3 3 10 10 − 1 − 10 2HDM+S Type-IV, tan β = 5 − 4 4 10 10 − − 5 − 5 10 2 10 10 expected ± 1 σ − 6 − 6 − 10 10 3 observed 10 1 10 60 1 10 60 1 10 60 m [GeV] Run 1 H → aa → µ µ τ τ m [GeV] m [GeV] a a a arXiv: 1505.01609 Run 1 H aa → → γ γ γ γ arXiv: 1509.05051 Run 2 H → aa → µ µ µ µ arXiv: 1802.03388 Run 2 H → aa → γ γ jj 10 8 aa) 10 7 8 aa) 10 arXiv: 1803.11145 aa) 7 → 10 6 Run 2 H aa bbbb 10 → → → → 7 10 B(H 6 arXiv: 1806.07355 10 B(H 5 B(H 10 6 Run 2 H → aa → bb µ µ 5 10 × 10 × 4 SM 10 × arXiv: 1807.00539 H SM tan β = 5 σ 4 H H SM σ 10 σ 5 σ 3 σ 10 95% CL on 10 σ 95% CL on 3 95% CL on 10 4 2 10 10 2 10 3 10 10 10 1 2 1 10 − 1 − 1 10 10 10 − − 2 10 2 10 1 − − 3 3 10 10 − 1 − 4 − 10 10 10 4 − 5 − − 10 5 10 2 10 − 6 10 − 6 10 − 3 1 10 60 10 1 10 60 1 10 60 m [GeV] m [GeV] m [GeV] a a a Elliot Reynolds Higgs Decays To Light Scalars 8 / 34

H → aa → ℓℓℓℓ - Overview arXiv:1802.03388 Z d H S Z d L int = 36 . 1 fb − 1 Dual-interpretation analysis: Pseudoscalar a from 2HDM+S † , 4 µ only Vector Z D from Hidden Abelian Higgs Model ‡ Dual-range analysis: Low mass: 1 GeV < m a < 15 GeV, 4 µ only High mass: 15 GeV < m a < 60 GeV, 4 µ + 2 µ 2 e + 4 e Select quadruplet with min: ∆ m = | m 12 − m 34 | Observable: � m � = ( m 12 + m 34 ) / 2 Dominant background EW, with additional fake lepton background † arXiv:1002.1956 ‡ arXiv:1412.0018 Elliot Reynolds Higgs Decays To Light Scalars 9 / 34