Dark Matter searches with the ATLAS detector

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XI CPAN DAYS (Centro Nacional de Física de Partículas, Astropartículas y Nuclear),

oviedo, | october 21-23 2019

Danijela bogavac (Ifae - barcelona) on behalf of the atlas collaboration

Red Temática de Física del LHC

21.10.2019

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introduction

• Standard Model (SM) is a very successful theory and has been found to be in agreement with experimental

measurements, but it can only explain 5% of the energy density in the Universe

• Dark Matter (DM) constitutes the dominant component of the total matter in the Universe

• Weakly interacting massive particles (WIMPs) are the most compelling candidates for DM and can be produced in collisions at the Large Hadron Collider (LHC)

XI CPAN DAYS Dark Matter searches with the ATLAS detector - Danijela Bogavac (IFAE-Barcelona) - 2 -

Known particles

LHC PRODUC

TION

Production of DM particles

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introduction

• Standard Model (SM) is a very successful theory and has been found to be in agreement with experimental

measurements, but it can only explain 5% of the energy density in the Universe

• Dark Matter (DM) constitutes the dominant component of the total matter in the Universe

• Weakly interacting massive particles (WIMPs) are the most compelling candidates for DM but can’t be observed directly at the LHC. A SM particle is needed to recoil against DM candidates

detection

SM particle:

quark, photon, Z, W, Higgs…

E_T^miss

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signal models

PIC/17.09.2019 Searches for strongly interacting SUSY particles - Danijela Bogavac (IFAE-Barcelona)

• ATLAS has a broad program of searches for Dark Matter candidates

Run II searches focus on simplified models with an additional mediator

Resonances Higgs as mediator

“Direct” searches

using ISR or associated production

Mediator searches

bump hunt for mediator decays to fermions

Higgs to invisible

0.1% branching ratio in the SM

Look for deviation from SM backgrounds

Look for mass peak above background

continuum

Look for enhancement of Higgs boson decays to

invisible

X + E

Tmiss

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signal models

Mediator searches

Higgs to invisible

continuum

invisible

X + E

Tmiss

Resonances Higgs as mediator

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300 400 500 600 700 800 900 1000 1100 1200

Events / GeV

−1

10 1 10 102

103

104

105

106

107

Data 2015+2016 Standard Model

) + jets ν ν Z(→

) + jets lν W(→

ll) + jets Z(→

+ single top t

t Diboson multijets + ncb

) = (500, 495) GeV )0

χ∼ ,

~b m(

)= (400, 1000) GeV , Mmed

(mDM

=6400 GeV ADD, n=4, MD

ATLAS

= 13 TeV, 36.1 fb-1

s

Signal Region

>250 GeV

miss

(j1)>250 GeV, ET

pT

[GeV]

miss

ET

300 400 500 600 700 800 900 1000 1100 1200

Data / SM

0.8 1

1.2 Stat. + Syst. Uncertainties

jet + E Tmiss

Signal model

• Dark Matter produced in association with jet(s) Strategy:

• selecting events with an energetic jet (pT > 250 GeV), up to three additional jets (pT > 30 GeV) and ETmiss (> 250 GeV)

• Z/W+jets and top-related backgrounds constrained using Monte Carlo simulation normalized to data in the control regions defined with leptons

• Z/W+jets Monte Carlo predictions reweighed to account for higher order corrections

Signal region

Most sensitive X+ETmiss channel

JHEP 01 (2018) 126

• Reached high precision in the background prediction uncertainty: 2% at low ETmiss and 7% in the TeV regime

2%

7%

2% 7%

q g

q¯

g_q

Z_A

χ

χ¯ g_χ

Good agreement with the SM prediction

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300 400 500 600 700 800 900 1000 1100 1200

Events / GeV

−1

10 1 10 102

103

104

105

106

107

) + jets lν W(→

ll) + jets Z(→

+ single top t

t Diboson multijets + ncb

) = (500, 495) GeV )0

χ∼ ,

~b m(

)= (400, 1000) GeV , Mmed

(mDM

ATLAS

= 13 TeV, 36.1 fb-1

s

Signal Region

>250 GeV

miss

(j1)>250 GeV, ET

pT

[GeV]

miss

ET

300 400 500 600 700 800 900 1000 1100 1200

Data / SM

0.8 1

jet + E Tmiss

Signal model

• Dark Matter produced in association with jet(s) Strategy:

• selecting events with an energetic jet (pT > 250 GeV), up to three additional jets (pT > 30 GeV) and ETmiss (> 250 GeV)

• Z/W+jets and top-related backgrounds constrained using Monte Carlo simulation normalized to data in the control regions defined with leptons

• Z/W+jets Monte Carlo predictions reweighed to account for higher order corrections

Signal region

Most sensitive X+ETmiss channel

JHEP 01 (2018) 126

• Reached high precision in the background prediction uncertainty: 2% at low ETmiss and 7% in the TeV regime

2%

7%

2% 7%

q g

q¯

g_q

Z_A

χ

χ¯ g_χ

Good agreement with the SM prediction

300 400 500 600 700 800 900 1000 1100 1200

Events / GeV

−1

10 1 10 102

103

104

105

106

107

) + jets lν

W(→

ll) + jets Z(→

+ single top t

t

Diboson multijets + ncb

) = (500, 495) GeV )0

χ∼ , b~ m(

)= (400, 1000) GeV , Mmed

(mDM

ATLAS

= 13 TeV, 36.1 fb-1

s

Signal Region

>250 GeV

miss

(j1)>250 GeV, ET

pT

[GeV]

miss

ET

300 400 500 600 700 800 900 1000 1100 1200

Data / SM

0.8 1

Signal region

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[GeV]

t1

m~

300 400 500 600

[GeV] 10 χ∼m

250 300 350 400 450 500 550 600

650 -1

=13 TeV, 36.1 fb s

1 0

χ∼ c

1→

~t production, t1

~ t1

~

All limits at 95% CL

ATLAS

=13 TeV, 3.2 fb-1

s ATLAS

theory) σSUSY

±1 Observed limit (

exp) 1 σ Expected limit (±

σexp

±2 Expected limit

+ mc

0

χ1

< m∼ t1

m~

+ mW

+ mb

0

χ1

> m∼ t1

m~

[GeV]

ZV

m

0 1000 2000

[GeV] χm

0 500

1000 Expected limit ^±²^σ^exp

exp) 1 σ Expected limit (±

PDF, scale)

theory

1 σ Observed limit (±

Relic Density (MadDM)

ATLAS

= 13 TeV, 36.1 fb-1

s

Vector Mediator Dirac Fermion DM

= 1.0 = 0.25, gχ

gq

95% CL limits

χ

= 2 m

ZV

m

Many models produce this signature

95% CL limits on vector mediator model

Observed (expected) limit: 1.55 TeV (1.85 TeV) for very light DM

candidates

jet + E Tmiss JHEP 01 (2018) 126

Compressed

supersummetric model

Significantly higher sensitivity at very low stop–neutralino mass difference

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[GeV]

mmed

200 400 600 800 1000 1200 [GeV]χm

0 50 100 150 200 250 300 350 400 450 500

χ

=2m mmed

ATLAS

=13 TeV, 36.1 fb-1

s

Vector mediator Dirac DM

l=0

=1, g gχ

=0.25, gq

Observed 95% CL σtheo

1 Observed ±

Expected 95% CL 1σ Expected ± Relic density

160 180 200 220 240 260 280 300 320 340 360

Events / 75 GeV

1 10 102

103

104

105 ^dataZ(→νν)γ

)γ lν W(→

Fake Photons + jets γ

ll)γ Z(→

=10/700 GeV /mmed

mχ

ATLAS

=13 TeV, 36.1 fb-1

s

Signal Region

[GeV]

miss

ET

160 180 200 220 240 260 280 300 320 340 360

Data/Bkg 0.5

1 1.5

• Dark Matter produced in association with a photon

photon + E Tmiss

Strategy:

• selecting events with a photon, large ETmiss and 0/1 jet

• three signal regions with ETmiss ranges between 150 GeV, 225 GeV, 300 GeV and above

• dominant backgrounds (Z+ɣ, W+ɣ, ɣ+jets) estimated in the dedicated control regions defined with leptons (Z+ɣ, W+ɣ) or at low ETmiss (ɣ+jets)

• fake background estimated via data driven methods

Eur. Phys J C 77 (2017) 393

Signal Region

Good agreement with the SM prediction

Observed (expected) limit: 1.2 TeV (1.07 TeV) for very light DM

candidates

95% CL limits on vector mediator model

Signal model

χ

χ¯ med

q¯

q

photonγ

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[GeV]

mmed

0 100 200 300 400 500 600 700 800 900 [GeV]χm

0 50 100 150 200 250 300 350 400

χ

= 2m mmed

Perturbative limit

σ)

±1 Expected limit ( Observed limit Relic density = 13 TeV, 36.1 fb-1

s

= 1.0 = 0.25, gχ

Axial-vector, Dirac, gq

µ ee+µ

ATLAS Expected limit (^±¹^σ⁾ Observed limit Relic density

[GeV]

miss

ET

−2

10

−1

10 1 10 102

103

104

Events / 10 GeV

[GeV]

miss

ET

0.6 0.8 1 1.2 1.4

Events / bkg

100 200 300 1000

Data ZZ WZ

Z+jets

Non-resonant-ll Others

Stat. + Syst.

inv)=0.3 ZH(ll+inv) with B(H→

=500, 100 GeV)x0.27 , mχ

DM(mmed

ATLAS

=13 TeV, 36.1 fb-1

s

ee

Z(ll) + E Tmiss

• Dark Matter produced in association with a Z boson decaying leptonically Signal model Strategy:

• targeting events with a pair of high-pT leptons (ee or µµ) and large ETmiss

• 76 GeV < mll < 106 GeV ➜ consistent with a Z boson

• ETmiss in ee and µµ channels used as a discriminating variable

• ZZ background estimated from Monte Carlo simulation, while WZ is normalized to data in the 3L control region

Good agreement with the SM prediction Signal region ee

95% CL limits on axial-vector mediator model

PLB 776 (2017) 318

med

q

¯

q Z Z ¯

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400 600 800 1000 1200 1400 200

300 400 500 600

700 _ATLAS

√s = 13 TeV, 36.1fb⁻¹

Mono-W/Z(qq): Vector, Dirac gSM = 0.25,gDM = 1.0

3

10− 2

10− 1

10−

1 10 102

103

104

105

Events / GeV

DataZ+jets W+jets

+ single top quark t

tDiboson Multijet

Background Uncertainty Pre-fit Background

= 100%)

inv H →

inv (B H →

Vector Mediator Model = 1 GeV = 600 GeV, mχ

mZ’

ATLAS

= 13 TeV , 36.1 fb-1

s

SR: merged topology 0 leptons, 0 b-tags, LP

400 600 800 1000 1200 1400

[GeV]

miss

ET

0.5 1 1.5

Data/SM

JHEP 10 (2018) 180

W/Z (hadronic) + E

Tmiss

Strategy:

• selecting events with ETmiss > 150 GeV and a hadronically decaying W/Z candidate

• considering both resolved and merged topologies

• Dark Matter produced in association with a W/Z boson decaying hadronically

• ETmiss for different b-tag multiplicities used as a discriminating variable

• Constraining Z and W backgrounds using lepton control regions

Signal Region Merged topology 0L and 0 b-tagged jets

Good agreement with the SM prediction 95% CL limits on

vector mediator model

Signal model q

q

χ

χ W! Z

Z^′

W/Z

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Axion-like particles

• Models with non-WIMPs DM candidates

• Axion - [the Nambu-Goldstone boson (NGB) from breaking of a color anomalous global

chiral U(1) symmetry which is spontaneously broken in the vacuum] strongly motivated since it solves also strong CP problem

• Axion-like particles (ALPs): good DM candidates

further NGBs from breaking of other global symmetries have couplings ~ 1/fALPs, but mALPs and fALPs are not related

• At the LHC, ALPs can be produced in association with:

Gluon W boson Z boson Photon

jet + E

Tmiss

W/Z (hadronic) + E

Tmiss

photon + E

Tmiss

NEW

•

The searches with the Full Run II dataset are currently in progress!

arXiv:1701.05379

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signal models

“Direct” searches

Mediator searches

Higgs to invisible

continuum

invisible

X + E

Tmiss

Resonances Higgs as mediator

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[TeV]

mq*

2 3 4 5 6 7 8

BR [pb]×A×σ

−4

10

−3

10

−2

10

−1

10

1 ^TheoryObserved 95% CL

Expected 95% CL 1 σ

± 2 σ

±

ATLAS Preliminary = 13 TeV, 139 fb-1

s

dijets

Strategy:

• selecting events with at least two jets (the leading jet pT >

420 GeV, the subleading jet pT > 150 GeV) with a rapidity difference between the two leading jets of |Ỏ𝝶^jj| < 0.6

• Sliding-window bump hunt in the invariant mass spectrum Signal model

Data is found to be in agreement with a

background only hypothesis with

p-value of 0.8

Excited quarks with masses below 6.7 TeV are excludes at 95% CL

p5 = 0 in nominal fit

ATLAS-CONF-2019-007

XI CPAN DAYS Dark Matter searches with the ATLAS detector - Danijela Bogavac (IFAE-Barcelona) -14 -

• Searches for Dark Matter candidates in dijet events

2 4 6 8

[TeV]

Reconstructed mjj

−1

10 1 10 102

103

104

105

106

107

108

Events

|y*| < 0.6

Fit Range: 1.1 - 8.1 TeV -value = 0.8

p

× 0.1

*, σ q

2 3 4 5 6 7 8

[TeV]

mjj

−2 0 2

Significance

ATLAS Preliminary

=13 TeV, 139 fb-1

s

Data

Background fit

BumpHunter interval = 4.0 TeV

*

*, mq

q

= 5.0 TeV

*

*, mq

q

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signal models

Mediator searches

Higgs to invisible

continuum

invisible

X + E

Tmiss

Resonances Higgs as mediator

Putting it all tog

ether!

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0 0.5 1 1.5 2 2.5 3 3.5 [TeV]

Z'V

m 0.2

0.4 0.6 0.8 1 1.2 1.4 1.6

[TeV] χm ATLAS

χ = 1 = 0, g = 0.25, gl

gq

Vector mediator, Dirac DM

Dijet

PRD 96, 052004 (2017) = 13 TeV, 37.0 fb-1

s Dijet

PRL 121 (2018) 0818016 = 13 TeV, 29.3 fb-1

s Dijet TLA

Preliminary ATLAS-CONF-2016-070 = 13 TeV, 15.5 fb-1

s Dijet + ISR

resonance tt

EPJC 78 (2018) 565

= 13 TeV, 36.1 fb-1

s

resonance t

t Dibjet

PRD 98 (2018) 032016

= 13 TeV, 36.1 fb-1

s

Dibjet

miss+X ET

Eur. Phys. J. C 77 (2017) 393 = 13 TeV, 36.1 fb-1

γ s

miss+ ET

JHEP 1801 (2018) 126 = 13 TeV, 36.1 fb-1

s +jet

miss

ET

PLB 776 (2017) 318

= 13 TeV, 36.1 fb-1

s +Z(ll)

miss

ET

JHEP 10 (2018) 180

= 13 TeV, 36.1 fb-1

s +V(had)

miss

ET

Z'V

χ = m

× m 2

= 0.12 h2

Ωc

Thermal Relic

SUMMARY of exclusion limits

• Vector mediators

• Similar results for axial-vector mediators

JHEP 05 (2019) 142

• Model dependent, comparisons different for different coupling values!

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signal models

“Direct” searches

Mediator searches

Higgs to invisible

continuum

invisible

X + E

Tmiss

Resonances Higgs as mediator

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Gluon-gluon fusion Associated VH production Vector Boson Fusion (VBF)

Production modes

• Many beyond Standard Model theories predict Higgs boson decays to invisible final states with the DM candidates as the final state particles

higgs to Invisible

W(qq)/Z(qq,ll) + ETmiss

Jet + ETmiss VBF + ETmiss

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Gluon-gluon fusion Associated VH production Vector Boson Fusion (VBF)

Production modes

• Many beyond Standard Model theories predict Higgs boson decays to invisible final states with the DM candidates as the final state particles

VBF + E

Tmiss

W(qq)/Z(qq,ll) + ETmiss

Jet + ETmiss

Strategy:

• selecting events with two jets with a rapidity difference |Ỏ𝝶^jj| > 4.8 and ETmiss > 180 GeV

• W/Z+jets backgrounds estimated in the dedicated control regions defined with a lepton(s)

• Maximum likelihood fit using three bins of mdijet starting at 1 TeV

• Good agreement with the SM prediction

VBF + ETmiss

Phys. Lett. B 793 (2019) 499

0 5 10 15 20 25

1 10 102

103

Events

ATLAS

fb-1

TeV, 36 13

1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1

1.5

Ratios

-ν

e e⁺ν e^-ν e⁺ν µ^-ν µ⁺ν ee µµ SR

Fake enriched W CR Z CR

Superimposed Data

inv=1 B B + S,

syst, B ±

prefit W & Z, postfit fakes

Stacked bkg.

W (strong) Z (strong) W (EW) Z (EW) e fakes

t t

multijet

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Run 2 V(had)H

Run 2 Z(lep)H

Run 2 VBF

Run 2 Combined

Run 1 Combined

Run 1+2 Combined

0 0.2 0.4 0.6 0.8 1

U pper limit on B

H→ inv ATLAS

= 8 TeV, 20.3 fb-1

s

= 13 TeV, 36.1 fb-1

s

Observed limit 1σ Expected limit ±

2σ Expected limit ± s = 7 TeV, 4.7 fb^-1

higgs to Invisible: combination Phys. Rev. Lett. 122, 231801 (2019)

VBF + ETmiss

Run I + Run II (2015-2016)

Observed (expected) limit @ 95% CL H(inv) BR < 0.26 (0.17)

Run II

Observed (expected) limit @ 95% CL H(inv) BR < 0.38 (0.21)

V(had) + ETmiss

Z(ll) + ETmiss

Three

channels

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Events / bin

1 10 102

103

104

105

106

107 ^Data

Z+jets + single top t

t W+jets Diboson SM Vh

Background Uncertainty Pre-fit Background mono-h Z’-2HDM

= 600 GeV = 1400 GeV, mA

mZ’

= 3.75 fb

Signal

σ

Preliminary ATLAS

= 13 TeV , 79.8 fb-1

s

SR : 0 lepton 2 b-tags

0

[GeV]

miss

ET

200 300 400 500 600 700 800

Data/SM ^0.8

1 1.2

0

q

¯

q Z⁰ h

A

¯ b

¯b

2 Higgs doublet model + Z’

Strategy:

• selecting events with ETmiss > 150 GeV and Higgs boson decay products

• two topologies: resolved (pair of separated jets) and

boosted (single large-radius jet), depending on the Higgs boson momentum

• Discriminating variables: ETmiss and dijet/large-R jet mass

• Z/W+jets and top-related backgrounds estimated in the control regions defined with 1/2 leptons

Signal model

ATLAS-CONF-2018-039

Combined Signal Region

• Associated production of Dark Matter and a Higgs boson (H → bb)

Good agreement with the SM prediction

95% CL limits on axial-vector mediator model

XI CPAN DAYS Dark Matter searches with the ATLAS detector - Danijela Bogavac (IFAE-Barcelona) - 21 - 1000 1500 2000 2500 3000

500 600 700 800 900 1000

ATLAS Preliminary

√s = 13 TeV, 79.8 fb⁻¹

h(bb) + E_T^miss: Z’+2HDM simplified model

tanβ = 1, g_Z = 0.8, mχ = 100 GeV, m_H = m_H^± = 300 GeV

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100 150 200 250 300 350 400

[GeV]

ma

200 400 600 800 1000 1200 1400 1600 1800 2000

[GeV] Am

ATLAS

, 36.1 fb-1

= 13 TeV s

Limits at 95% CL Observed Expected

2HDM+a, Dirac DM

χ = 1 = 10 GeV, g mχ

β = 1 = 0.35, tan sinθ

H± H = m

A = m m

= 600 GeV mA

+ mh

= ma

mA

= ma

mA

> 20%

/ma

Γ

+Z(ll)

miss

ET

PLB 776 (2017) 318

+Z(ll)

miss

ET

) b

miss+h(b ET

PRL 119 (2017) 181804

) b

miss+h(b ET

γ) +h(γ

miss

ET

PRD 96 (2017) 112004

γ) +h(γ

miss

ET

) q

miss+Z(q ET

JHEP 10 (2018) 180

) q

miss+Z(q ET

=7,8 TeV;4.7,20.3 fb-1

h(inv) s

JHEP 11 (2015) 206,

=7,8 TeV;4.7,20.3 fb-1

h(inv) s

SUMMARY of exclusion/observed limits

PUTTING IT ALL TOGETHER

Exclusion sensitivity dominated by ETmiss+h(bb) and ETmiss+Z(ll) H to invisible used to set limits on very low values of ma

JHEP 05 (2019) 142

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conclusion

•

The nature of the Dark Matter remains one of the main questions in particle physics

•

ATLAS has a broad program of searches for Dark Matter candidates

•

Run II searches mainly focus on simplified models

•

Higgs boson at centre of the Standard Model and its extensions

•

Many searches with the Full Run II dataset are currently in progress

•

Run 3 will double the dataset (

~

350 fb

^-1

to be delivered)

•

Full HL-LHC program will extend significantly the reach (one order of magnitude more data!)

thank you for your attention!

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backup

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W → eν

W → μν

Z → ll Top

25

jet + E Tmiss

Control regions

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W → eν

W → μν

Z → ll Top

26

jet + E Tmiss

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photon + E Tmiss

Signal region definition

Systematic uncertainties

Observed event yields

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photon + E Tmiss

Control regions

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Z(ll) + E Tmiss

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W/Z (hadronic) + E

Tmiss

Systematic uncertainties

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SUMMARY of exclusion limits

Axial-vector mediators

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2I CPAN DAYS Dark Matter searches with the ATLAS detector - Danijela Bogavac (IFAE-Barcelona) - 32 -

VBF + E

Tmiss

Systematic uncertainties Distribution of event yields in the signal

region for m

j j

(left) and E

Tmiss

(right)

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2 Higgs doublet model + Z’

Control regions Signal region

definition Systematic uncertainties