Dark Matter searches with theATLAS Detector
Lomonosov 2021

Study of VH non-hadronic category

Zirui Wang
on behalf of the ATLAS collaboration
24 August. 2021

Introduction

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• Empirical evidence of DM from astrophysical observations at different scales• Most of the matter content of the universe is transparent• Appealing scenario: DM is a Weakly Interacting Massive Particle

arXiv:1810.09420• Assuming DM-SM weak interaction enables different searches:• direct detection, nuclear recoils from DM-nuclei scattering• indirect detection, products from DM annihilation• colliders, DM production in high-energy collisions• DM production at colliders• No direct trace in the detector, but could createa pT imbalance (MET) ⇒ associated productionof dark matter and SM particles

Outline

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• Overview of Dark Matter models• Recent Dark Matter searches *• Jet + MET• H(bb) + MET• H(γγ) + MET• Z(ll) + MET• tW/tj + MET• Combinations of Dark Matter searches• s-channel mediator• 2HDM + a• Higgs portal*Caveat: Only a small selection of full Run 2 analyses presented today3Overview of dark matter models

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For DM searches, theoretical benchmarks are necessary to sharpen the regions ofinterest• To optimize searches and characterize a possible discovery• Define a theoretical framework for comparison with non-collider results

Simplified s-channel mediator model
Small set of free parameters. Interesting
interplays between Mono-X searches andresonance searches.

Higgs portal models
Search for enhancement ofinvisibly decays which increase
BR(H→inv) (~0.1% in SM).

2HDM+aTwo-Higgs doublet extensions with a pseudoscalar a. Gauge-invariant. Richer kinematics +phenomenology

SUSY
Simplified R-parity
conserving model

2HDM+Z’
Two-Higgs doublet extensions
with a vector Z’

Outline• Overview of Dark Matter models• Recent Dark Matter searches• Jet + MET• H(bb) + MET• H(γγ) + MET• Z(ll) + MET• tW/tj + MET• Combinations of Dark Matter searches• s-channel mediator• 2HDM + a• Higgs portal

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Jet + MET• Selection: MET> 200 GeV, ΔΦ(jet, MET) cut
to reduce the multijet contribution.
• Dedicated control regions (CRs) to estimate
V+jets, ttbar and single-top processes.
• Results: simultaneous fit to the 𝑝𝑇 recoil(hard component of MET) distributions inSR and CRs.
• Uncertainties reduced to a few percent
level in each bin for SM predictions.

Lomonosov2021 - Zirui Wang

6Phys. Rev. D 103 (2021) 112006

Simplified axial-vector model

Simplified pseudo-scalar modelMono-H(bb)• Associated production of Dark Matter and aHiggs boson ⇒Larger production rate than ISRbased production mode.
• Both resolved and merged topologies withdifferent H→bb reconstructions employed.
• Results: simultaneous fit to the Higgs
mass distributions in SR and CRs.

2HDM+Z’, mZ’ vs mA scan

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ATLAS-CONF-2021-006

2HDM+a, ma vs mA scan

Mono-H(γγ)• Comparing to mono-H(bb), triggered using
the photon pair, allowing for much lower
and better resolved MET in the event.
• S+B fits performed in analysis categories
simultaneously.

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arXiv:2104.13240
2HDM+Z’, mZ’ vs mA scan

2HDM+a, sin θ scan

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Mono-Z(ll)•••Select events with a leptonically-decaying Z against
significant MET.
Results: simultaneous fit in SR and CRs.
Observed BR(H→inv) < 0.18 @ 95% C.L.

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ATLAS-CONF-2021-029
Simplified axial-vector model

2HDM+a, ma vs mA scan9

tW/tj + MET• Search for dark matter in the context of 2HDM+aLomonosov2021 - Zirui Wang

10arXiv:2011.09308

2HDM+a, ma vs mH± scanOutline• Overview of Dark Matter models• Recent Dark Matter searches• Jet + MET• H(bb) + MET• H(γγ) + MET• Z(ll) + MET• tW/tj + MET• Combinations of Dark Matter searches• s-channel mediators• 2HDM + a• Higgs portal

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S-channel – spin 1 mediators• Searches use simplified models with a spin-1
particle as the mediator• Vector and axial vector mediator• Resonance searches and MonoX searches withsensitivities varied as a function of differentcoupling values of the model.

Simplified vector model

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MonoX searches

12Resonance searches

Simplified axial-vector model• Analyses dominating the sensitivity are:
• MET signatures: Mono-jet and mono-photon• Non-MET signatures: High-mass di(b)-jet resonances, TLA di-jet, Dijet+ISR(boosted and resolved), Dilepton resonances
ATL-PHYS-PUB-2021-006

Compare to direct detection

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Results translated into spin-dependent and spin-independentDM-nucleon elastic scattering cross-section limits ⇒compared to direct searches

Axial-vector mediator leads
to a SD interaction

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ATL-PHYS-PUB-2021-006

Vector mediator leads to aSI interaction• ATLAS results are particularly competitive for low DM masses.
• Translation is model-dependent. LHC limits hold exclusively for considered models.

s-channel – spin 0 mediators

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ATL-PHYS-PUB-2021-006• Searches with scalar (φ) and pseudoscalar (a) as the mediator• Dark Matter production via (pseudo)scalar mediator inassociation with HF• Mediator decays into two dark matter particles Χ, with MET
signature.
• Dominated by t/tt/bb+MET analyses, mono-Jet, and tt resonances.
• The strongest limits are placed by tt+MET 2L final state.

Simplified pseudo-scalar model

Simplified scalar modelCombination of 2HDM+aLomonosov2021 - Zirui Wang

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• Most sensitive searches updated to full Run 2 luminosity• Statistical combination of MET+h(bb) and MET+Z(ll) analyses, which improves the sensitivity.
• Significant complementarity from different channels.
ATLAS-CONF-2021-036
ma vs mA scanmA vs tanβ scanCombination of 2HDM+aLomonosov2021 - Zirui Wang

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• Most sensitive searches updated to full Run 2 luminosity• Statistical combination of MET+h(bb) and MET+Z(ll) analyses, which improves the sensitivity.
• Significant complementarity from different channels.
ATLAS-CONF-2021-036
Sinθ scanmχ scan

Higgs→invisible combination• Combining direct measurements toprobe with higher sensitivity ⇒Statistically combining VBF+MET,
tt+MET (tt2L + tt0L), and Run1
combination results• Observed BR(H→inv) < 0.11 @ 95% C.L.
(~0.1% in SM).
• Assuming DM particles are either scalaror Majorana fermions ⇒ Translate
results into a DM-nucleon elastic
scattering cross-section limit.
• Significant complementarity between
LHC and direct detection experiments• A preliminary combination ⇒ Moreresults such as Z(ll)+MET, VBF+γ+MET tobe added to the final Run 2
combination.

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ATLAS-CONF-2020-052

17Summary

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• A large number of searches for DM candidates has been performed by ATLAS.
Selected full Run 2 searches and combination analyses presented.

• Interpretation in view of many different DM models.
• Complementarity from different signatures reached.
• Complementarity with non-collider searches observed.

• There are still many more ATLAS full Run 2 results to be expected. Stay tunedfor updates!

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Thanks

BackupDirect detection experiments

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ATLAS Run 2 dataset• Solenoid Magnet: 2T• Toroid Magnets: 0.5-1TLarge dataset collected by ATLAS in Run 2 (20152018) with 139 𝑓𝑏 −1 integrated luminosity
ATLAS public results

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• Inner detector (|η|<2.5):
Precise tracking and vertexing, e/πseparation.
• EM calorimeter (|η|<3.2):e/γ trigger, identification andmeasurement.
• Hadronic calorimeter (|η|<4.9):
Trigger and measurement of jetsand E 𝑚𝑖𝑠𝑠.
𝑇• Muon Spectrometer (|η|<2.7):
Muon trigger and tracking.

tt+MET 2L SR distributions

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bb+MET SR distributions

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Mono-H(γγ) selection/ compare to mono-H(bb)Lomonosov2021 - Zirui Wang

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