Dark Matter and SUSY at ATLAS IMPRS Young Scientist Workshop Friday, - - PowerPoint PPT Presentation

Dark Matter and SUSY at ATLAS

Nicolas Köhler

Max Planck Institute for Physics 
 (Werner-Heisenberg-Institut) Friday, 7th September 2018

IMPRS Young Scientist Workshop

/ 13 Ringberg Workshop 2018 Nicolas Köhler 2

How does SUSY explain Dark Matter?

• Neutral and weakly interacting particle
• Stable particle - Assume R-parity conservation - obtain stable LSP

/ 13 Ringberg Workshop 2018 Nicolas Köhler 2

How does SUSY explain Dark Matter?

• Neutral and weakly interacting particle
• Stable particle - Assume R-parity conservation - obtain stable LSP
• Possibly neutralino

˜ χ0

1

/ 13 Ringberg Workshop 2018 Nicolas Köhler 2

How does SUSY explain Dark Matter?

• Neutral and weakly interacting particle
• Stable particle - Assume R-parity conservation - obtain stable LSP
• Possibly neutralino

˜ χ0

1

˜ G

˜ G G

Gravity

• r gravitino

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What is the lightest supersymmetric particle?

• Depending on SUSY breaking mechanism
• Most popular candidates:

mSUGRA
 (minimal SuperGravity) GMSB
 (Gauge mediated SUSY Breaking)

• B. Schneider, SUSY18, Barcelona
• U. Uwer, Lecture Notes

/ 13 Ringberg Workshop 2018 Nicolas Köhler 3

What is the lightest supersymmetric particle?

• Depending on SUSY breaking mechanism
• Most popular candidates:

mSUGRA
 (minimal SuperGravity) GMSB
 (Gauge mediated SUSY Breaking) Lightest neutralino

• B. Schneider, SUSY18, Barcelona
• U. Uwer, Lecture Notes

/ 13 Ringberg Workshop 2018 Nicolas Köhler 3

What is the lightest supersymmetric particle?

• Depending on SUSY breaking mechanism
• Most popular candidates:

mSUGRA
 (minimal SuperGravity) GMSB
 (Gauge mediated SUSY Breaking) Lightest neutralino Gravitino

• B. Schneider, SUSY18, Barcelona
• U. Uwer, Lecture Notes

/ 13 Ringberg Workshop 2018 Nicolas Köhler 3

What is the lightest supersymmetric particle?

• Depending on SUSY breaking mechanism
• Most popular candidates:

mSUGRA
 (minimal SuperGravity) GMSB
 (Gauge mediated SUSY Breaking) Lightest neutralino Gravitino

• B. Schneider, SUSY18, Barcelona
• U. Uwer, Lecture Notes

Always search for missing transverse energy Emiss

T

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Neutralino from gaugino decays

• Search for 3 leptons
• No b-tagged jets
• Transverse mass of and > 110 GeV

arxiv:1803.02762

m`+`− ∼ mZ ` Emiss

T

• Dominating SM processes: 


Diboson

• No excess above SM pred.

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Neutralino from gaugino decays

• Search for 3 leptons
• No b-tagged jets
• Transverse mass of and > 110 GeV

arxiv:1803.02762

m`+`− ∼ mZ ` Emiss

T

• Dominating SM processes: 


Diboson

• No excess above SM pred.

Excluded

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• TeV-stop favoured to solve hierarchy problem
• Consider decay into top quark and neutralino

˜ t ˜ t p p ˜ χ0

1

t ˜ χ0

1

t

Nicolas Köhler

Neutralino from stop decays

Ringberg Workshop 2018

/ 13 Ringberg Workshop 2018 5

• TeV-stop favoured to solve hierarchy problem
• Consider decay into top quark and neutralino
• Consider fully-hadronic top quark decays

˜ t ˜ t t W ˜ χ⌥

1

W p p ˜ χ0

1

b q q b ˜ χ0

1

q q

Nicolas Köhler

Neutralino from stop decays

Ringberg Workshop 2018

/ 13 Ringberg Workshop 2018 5

• TeV-stop favoured to solve hierarchy problem
• Consider decay into top quark and neutralino
• Consider fully-hadronic top quark decays
• No leptons, multiple jets, large

˜ t ˜ t t W ˜ χ⌥

1

W p p ˜ χ0

1

b q q b ˜ χ0

1

q q

Nicolas Köhler

Neutralino from stop decays

Emiss

T

Ringberg Workshop 2018

/ 13 Ringberg Workshop 2018 5

• TeV-stop favoured to solve hierarchy problem
• Consider decay into top quark and neutralino
• Consider fully-hadronic top quark decays
• No leptons, multiple jets, large

˜ t ˜ t t W ˜ χ⌥

1

W p p ˜ χ0

1

b q q b ˜ χ0

1

q q

https://www.quantumdiaries.org/

• Decay products of top strongly collimated
• Jet clustering with large radius parameter

allows to collect the top in single object

• Discriminate against SM processes not

containing top quarks

• Dominating SM processes left: and 


+jets

For m˜

t1 m˜ χ0

1

t¯ t

Z(→ νν)

Nicolas Köhler

Neutralino from stop decays

Emiss

T

Ringberg Workshop 2018

/ 13 Ringberg Workshop 2018 5

• TeV-stop favoured to solve hierarchy problem
• Consider decay into top quark and neutralino
• Consider fully-hadronic top quark decays
• No leptons, multiple jets, large

˜ t ˜ t t W ˜ χ⌥

1

W p p ˜ χ0

1

b q q b ˜ χ0

1

q q

https://www.quantumdiaries.org/

• Decay products of top strongly collimated
• Jet clustering with large radius parameter

allows to collect the top in single object

• Discriminate against SM processes not

containing top quarks

• Dominating SM processes left: and 


+jets

For m˜

t1 m˜ χ0

1

t¯ t

Z(→ νν) No excess above SM expectation found


• > Calculate exclusion limits:

Nicolas Köhler

arxiv:1709.04183

Neutralino from stop decays

Emiss

T

Ringberg Workshop 2018

Excluded

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https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CombinedSummaryPlots/SUSY/

• No top squark found in all decay

scenarios

˜ t ˜ t ˜ χ±

1

˜ χ⌥

1

p p b ˜ χ0

1

W b ˜ χ0

1

W

˜ t ˜ t p p b f f ˜ χ0

1

b f f ˜ χ0

1

˜ t ˜ t p p ˜ χ0

1

t ˜ χ0

1

t

Neutralino from stop decays

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• Consider production of ˜

u1, ˜ d1, ˜ c1, ˜ s1

arxiv:1712.02332

• Veto leptons
• At least two jets with 


> 50 GeV

• Large missing

transverse energy

• Requirements on scalar

sum of transverse momenta

Neutralino from light squark decays

pT

Excluded

/ 13 Ringberg Workshop 2018 Nicolas Köhler 7

• Consider production of ˜

u1, ˜ d1, ˜ c1, ˜ s1

arxiv:1712.02332

• Veto leptons
• At least two jets with 


> 50 GeV

• Large missing

transverse energy

• Requirements on scalar

sum of transverse momenta

• Dominating SM

backgrounds: W+jets,

Neutralino from light squark decays

t¯ t pT

Excluded

/ 13 Ringberg Workshop 2018 Nicolas Köhler 8

• Veto leptons
• At least four high-energetic jets
• Large
• Discriminating

variable: 
 


• Dominating SM

backgrounds: 
 W+jets,

• No excess above SM

expectation found

Neutralino from gluino decays

Emiss

T

t¯ t P

jets

pT+ Emiss

T

/ 13 Ringberg Workshop 2018 Nicolas Köhler 8

arxiv:1712.02332

• Veto leptons
• At least four high-energetic jets
• Large
• Discriminating

variable: 
 


• Dominating SM

backgrounds: 
 W+jets,

• No excess above SM

expectation found

Neutralino from gluino decays

Emiss

T

t¯ t P

jets

pT+ Emiss

T

Excluded

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Gravitino as the LSP

m ˜

G ⌧ 1 GeV

arxiv:1802.03158

• Require at least two photons with >75 GeV
• Large
• Large
• Dominating SM

backgrounds: 
 production
 +jets production
 Multijet production

• No excess above SM

expectation found

γγ γ ET Emiss

T

Excluded

P

jets

pT + P

γ

pT

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Did we miss anything?

• What if the NLSP does not decay instantaneously?
• Secondary displaced vertex of interest appears in the event

arxiv:1112.0180

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Long-lived neutralino

arxiv:1409.5542

• Exploit finely segmented LAr

EM calorimeters

• Look at difference in 


z-coordinate between primary vertex and closest approach

• f photon to beam line

Emiss

T

• If neutralino has non-zero lifetime, 


two displaced photons are present

• Require pair of photons and

∆zγ

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Long-lived neutralino

arxiv:1409.5542

• Exploit finely segmented LAr

EM calorimeters

• Look at difference in 


z-coordinate between primary vertex and closest approach

• f photon to beam line

Emiss

T

• If neutralino has non-zero lifetime, 


two displaced photons are present

• Require pair of photons and

∆zγ

/ 13 Ringberg Workshop 2018 Nicolas Köhler 12

Long-lived neutralino

arxiv:1409.5542

• Photons reach EM calorimeter

with slight time delay

• Measure time of arrival
• Fit in bins of
• SM background: One photon is

misidentified electron/jet

• No excess above SM

expectation

tγ tγ ∆zγ

/ 13 Ringberg Workshop 2018 Nicolas Köhler 12

Long-lived neutralino

arxiv:1409.5542

• Photons reach EM calorimeter

with slight time delay

• Measure time of arrival
• Fit in bins of
• SM background: One photon is

misidentified electron/jet

• No excess above SM

expectation

tγ tγ ∆zγ

Excluded

/ 13 Ringberg Workshop 2018 Nicolas Köhler 13

Summary

• Supersymmetry is one of the most favoured theoretical

frameworks for beyond-SM physics

• Inherently contains Dark Matter candidate(s): , , …
• ATLAS has a broad SUSY physics program
• No hint for SUSY or Dark Matter found so far
• Lots of SUSY models already excluded
• Focus on systematically scanning through SUSY models in
• rder to not miss any realisation of SUSY

˜ χ0

1

˜ G