Mark Neubauer
University of Illinois
(on behalf of the ATLAS Collaboration)
International Conference on High Energy Physics (ICHEP) Valencia, Spain July 5, 2014
High Mass Higgs Boson
Searches at ATLAS
University of Illinois
• A new era in particle physics. The discovery of a particle consistent with the SM Higgs boson with mass ~125 GeV
opens up a new window to search for beyond-the-SM physics
• SM Higgs or something else? There is a lot of room for non-SM interpretations of this Higgs particle. Examples include SUSY, composite Higgs, Higgs portal to dark matter
How can we exploit the Higgs sector to look for new physics?
• Festina Lente... We search for
① non-SM properties (couplings, JPC, decays) of the Higgs boson
② additional Higgs bosons
Introduction
University of Illinois
• A new era in particle physics. The discovery of a particle consistent with the SM Higgs boson with mass ~125 GeV
opens up a new window to search for beyond-the-SM physics
• SM Higgs or something else? There is a lot of room for non-SM interpretations of this Higgs particle. Examples include SUSY, composite Higgs, Higgs portal to dark matter
How can we exploit the Higgs sector to look for new physics?
• Festina Lente... We search for
① non-SM properties (couplings, JPC, decays) of the Higgs boson
② additional Higgs bosons
Introduction
à ATLAS searches for heavier neutral particles with Higgs-like properties is the focus of this talk
University of Illinois
• 2HDM: Adding a second electroweak doublet to the Higgs sector is one of the simplest extensions to the SM
§ 5 Higgs bosons
Two Higgs Doublet Models (2HDMs)
• The Higgs sector of 2HDMs are described by:
§ 4 Higgs masses
§ tan β (ratio of vacuum expectation values)
§ Mixing parameter α (mixing between two neutral CP-even states h, H)
• The minimal supersymmetric SM (MSSM) is of this type
• 2HDMs have rich phenomenology and are compatible with a SM-like Higgs boson with mass ~125 GeV
CP-even neutral Higgses CP-odd neutral Higgs Charged Higgses
University of Illinois
2HDM Higgs to Weak Bosons
ATLAS-CONF-2013-27
• Search for a heavier neutral CP-even
partner (H) to the 125 GeV “light” Higgs (h)
§ Use HàWW(*)àevµv decay channel
§ Split into 0-jet (ggF) and 2-jet (VBF) channels
§ Use neural network to separate signal from background
ggF
VBF
0 jet 2 jet
University of Illinois
2HDM Higgs to Weak Bosons: Results
ATLAS-CONF-2013-27
à No evidence for a
signal found in the mass range of [135, 300] GeV à Limits set in cos(α) vs.
mH plane for Type I & II using 13 fb-1 @ 8 TeV
0 jet 2 jet
University of Illinois
2HDM Higgs to Weak Bosons: Results
ATLAS-CONF-2013-27
à No evidence for a
signal found in the mass range of [135, 300] GeV à Limits set in cos(α) vs.
mH plane for Type I & II using 13 fb-1 @ 8 TeV
Type I: One Higgs doublet couples to vector bosons, the other to fermions
Type II: “MSSM-like” model, where one doublet couples to up-type quarks, the other to down-type quarks
Type I Type II
0 jet 2 jet
tanβ=20 tanβ=20
University of Illinois
• Interesting signature: decay of a heavier Higgs into lighter ones
• Search for BSM Higgs decay chain including a heavy Higgs (H), intermediate charged Higgs (H±) and light Higgs (h)
§ The light neutral Higgs (h) is assumed to have the same mass as the Higgs boson observed @ 125 GeV
2HDM Multi-Higgs Cascade
• Final state:
§ Require one hadronically decaying W boson and one leptonically decaying W boson
• Main background is
• Boosted decision trees (BDTs) are used to separate signal from the background
Phys Rev D 89, 032002 (2014)
125 GeV SM-like Higgs decaying to b bbar
W
+W
−bb
tt
H
h H±
W ± W ∓
g g
b
b
University of Illinois
2HDM Multi-Higgs Cascade: Results
Phys Rev D 89, 032002 (2014)
Loss of sensitivity due to poor separation from ttbar background
• No significant signal observed in the BDT distributions
• Derive 95% CL upper limits on x-section / σtheory(SM-like)
Sensitive to a heavy
Higgs produced via gluon fusion at the SM rate
H
H h
University of Illinois
• Search for higher mass CP-even Higgs in the mass ranges
§ [260, 1000] GeV for the SM lineshape
§ [300, 1000] GeV for the narrow width lineshape (NWA)
v Narrow width predicted by some BSM models
• Includes , with where
• Treat 125 GeV Higgs as background
• Transverse mass mT used to
discriminate signal and background in 0,1,2 jet final states
Heavy Scalar Boson decaying to WW
ATLAS-CONF-2013-067
0 jet
1 jet
WW → ℓ ντν τ → ℓ νν
ℓ ≡ e, µ
University of Illinois
• No signal observed for SM or NWA lineshape hypotheses
Heavy Scalar Boson decaying to WW
ATLAS-CONF-2013-067
• For the SM width, Higgs masses in the range [260, 642] GeV are excluded at 95% CL
SM Lineshape NWA
University of Illinois
• 4.6 @ 7 TeV + 20.7 fb-1 @ 8 TeV
• 200 ≤ MH ≤ 1000 GeV
• Final states: 4e, 4µ, 2e2µ, 2µ2e
• VBF-like,VH-like, ggF-like categories
§ VBF: 2 high pT jets w/large rapidity gap and mjj
§ VH: additional e/µ
§ ggF: all other
Heavy Scalar Boson decaying to ZZ
ATLAS-CONF-2013-013
ggF VBF
§ Low BR, clean signature, high S/B
§ Fully-reconstructed m4l mass
§ ZZ background from MC, reducible ll+jets and ttbar backgrounds using data-driven methods
§ Statistically limited at high mass
University of Illinois
• Extension of the techniques developed for the discovery of h(125)→γγ to search for additional narrow resonances
decaying into γγ in an extended mass range
§ Predicted by several extensions of SM: e.g. 2HDMs
§ Mγγ spectrum fitted with analytical descriptions of signal and background distributions [h(125) contribution is included in background]
§ No significant excess found
Heavy Scalar Boson decaying to γγ
ATLAS-CONF-2014-31
BG-only fit
95% CL upper limit on x-section×BR(Xàγγ) vs. M(X)
University of Illinois
• SM di-Higgs production (~10 fb) not observable in Run1
• Observable (~pb) in SM extensions: 2HDMs, composite models
§ E.g. heavy Higgs Hàhh, anomalous Higgs self coupling λhhh
§ Low rate à counting experiment
§ BG shape (normalization) from Mbbγγ (Mγγ sidebands) in < 2 b-tag CR
§ Small excess (2.4 σ) seen in the non-resonant search
Di-Higgs Production in bbγγ channel
arXiV:1406.5053
95% CL upper limit on σ×BR for a narrow resonance decaying to hhàbbγγ
University of Illinois
• Search for invisible decay of a Higgs boson (H) produced in association with a Z boson decaying into two leptons
§ Allowed in SM extensions (SUSY, extra dimensions, Higgs portal DM,…)
§ Dominant backgrounds are ZZàllvv and WZàlllv
v Estimated using simulation and validated in control regions
Invisibly decaying Higgs
PRL 112, 201802 (2014)
University of Illinois
• LHC Run 1 ends with a great success – discovery of a Higgs boson and measurements of its properties (consistent with those predicted by the SM thus far)
• Searches for additional Higgs bosons at higher masses are
well-motivated by BSM models, DM observations, and the spirit of exploration
à No evidence for additional Higgs-like particles have been found, but more Run 1 results from ATLAS are still to come!
• With higher luminosity and collision energy in LHC Run 2 and an upgraded ATLAS detector, more sensitive searches for heavy Higgs bosons are on the horizon.
• We are entering an exciting new realm of Higgs sector exploration!
Summary and Outlook
University of Illinois
Extras
University of Illinois
• ATLAS Collaboration. “Search for the Higgs boson in the H→WW→ℓνjj decay channel at √s=7 TeV with the ATLAS detector”, Phys. Lett. B 718 (2012) 391-410
• ATLAS Collaboration. “Search for a Standard Model Higgs boson in the mass range 200–600 GeV in the
H→ZZ→ℓ+ℓqq decay channel with the ATLAS detector”, Phys. Lett. B 717 (2012) 70-88
• ATLAS Collaboration. “Search for a Standard Model
Higgs boson in the H→ZZ→ℓ+ℓ−νν decay channel using 4.7 fb−1 of √s=7 TeV data with the ATLAS detector”,
Phys. Lett. B 717 (2012) 29-48
Other Heavy Higgs search results
University of Illinois
2HDM Higgs to Weak Bosons: Results
ATLAS-CONF-2013-27 Type I
tanβ=1 tanβ=3
tanβ=6 tanβ=20 tanβ=50
University of Illinois
2HDM Higgs to Weak Bosons: Results
ATLAS-CONF-2013-27 Type II
tanβ=1 tanβ=3
tanβ=6 tanβ=20
University of Illinois
• Identify leptonic W decay
• Reconstruct light Higgs h0 from two b-jets
• Construct H± candidate from h0 and W candidates that gives the largest m(H±)
• Construct H0 from bbWW system
2HDM Multi-Higgs Cascade: Reconstruction
Phys Rev D 89, 032002 (2014)