Spyros Argyropoulos

Probing the dark sector with b-quarks with the ATLAS detector

Spyros Argyropoulos on behalf of the ATLAS collaboration

1

2

Most of the matter in the galaxies must be dark

Zwicky, 1933Rubin et al, 1962

3

Half a century later: much more data but still no hint at the nature of the dark sector

Can the recently discovered Higgs boson tell us something about the dark sector?

4

Standard Model

Dark SectorHiggs Dark scalar

Higgs

Higgs sector connected with dark sector in many theories

Two possibilities to be discussed today:

1. Extended Higgs sector portal • DM interacts only via extended Higgs sector • DM produced in association with Higgs • DM particles are invisible → ETmiss

2. Hidden valley • Dark sector containing light long-lived particles • Higgs as communicator with dark sector • Long lifetime → displaced decays

➡ Mono-Higgs to b-quarks ➡ Displaced decays to b-quarks

5

• DM produced with SM-like Higgs = ETmiss + b-jets ➡one of the most sensitive channels

JHEP 05 (2019) 142

Missing Energy

candidateHiggs

Mono-Higgs to b-quarks

ATLAS-CONF-2021-006

Models used

6

• Based on extensions of usual 2 Higgs doublet model - 5 Higgs bosons: (h, H, A, H±)

• Two benchmark models

2HDM + Z’ 2HDM + a (pseudo-scalar)

gluon-fusion b-associated production

➡ mZ’ can be in multi-TeV range ➡ benchmark for highly boosted

regime ➡ largely excluded by di-jet search

and B-physics

➡ Common benchmark for collider & direct/indirect searches ➡ Large array of signatures lending → combinations ➡ Two production modes: ggF (low tanβ) and bbA (high tanβ) ➡ First result probing region with ≥3 b-jets

<latexit sha1_base64="g+5c1MBENfMGXatEC0FvWeOq3xQ=">AAAB9XicdVBNS8NAEN34WetX1aOXxSJ4KkmNbb0VvXisYD+giWWz3bZLN5uwO1FK6P/w4kERr/4Xb/4bN20FFX0w8Hhvhpl5QSy4Btv+sJaWV1bX1nMb+c2t7Z3dwt5+S0eJoqxJIxGpTkA0E1yyJnAQrBMrRsJAsHYwvsz89h1TmkfyBiYx80MylHzAKQEj3Xqah9gDIr2AAekVinbpvFYpuxVsl2y76pSdjJSr7qmLHaNkKKIFGr3Cu9ePaBIyCVQQrbuOHYOfEgWcCjbNe4lmMaFjMmRdQyUJmfbT2dVTfGyUPh5EypQEPFO/T6Qk1HoSBqYzJDDSv71M/MvrJjCo+SmXcQJM0vmiQSIwRDiLAPe5YhTExBBCFTe3YjoiilAwQeVNCF+f4v9Jq1xyzkr2tVusXyziyKFDdIROkIOqqI6uUAM1EUUKPaAn9GzdW4/Wi/U6b12yFjMH6Aest0+0MZKo</latexit>

⇠ tan�

JHEP 06 (2014) 078 Phys.Dark Univ. 27 (2020) 100351

60 80 100 120 140 160 180 200 220 240 260 280 [GeV]bbm

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eV DataSM VhDibosonW+(bb,bc,cc,bl)W+(cl,l)tt

Single topZ+(bb,bc,cc,bl)Z+(cl,l)tth+ttVBackground Uncertainty

20)×Mono-h Z'-2HDM () = (1400,1000) GeV

A,m

Z'(m

= 1.89 fbsignalσ

ATLAS Preliminary -1 = 13 TeV, 139 fbs

Resolved: 0-lepton-tag Signal Regionb2

[200, 350) GeV∈ missTE

60 80 100 120 140 160 180 200 220 240 260 280 [GeV]bbm

0.8

1

1.2

Dat

a/SM

Analysis

7

ETmiss < 500 GeV use R=0.4 calorimeter jets

use R=1.0 calorimeter jets

+ variable-R track-jets for

b-tagging

Resolved Merged

•Look for an excess of events in the mass spectrum around mH=125 GeV

•Main backgrounds from top and Z + heavy flavour •constrained by 1/2-lepton control regions

•Simultaneous fit in several regions •{0,1,2 leptons} x {4 or 5 ETmiss bins} x {2 or ≥3 b-jets}

ETmiss > 500 GeV

ATLAS-CONF-2021-006

500 1000 1500 2000 2500 3000 [GeV]Z'm

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1000

[GeV

]A

m

Expected Limitexpσ1 ±

expσ2 ±

arXiv:1707.01302-1 139 fb→ -136.1 fb

h -

mZ'

= m

A

Kin.

limit

: m

ATLAS Preliminary-1 = 13 TeV, 139 fbs

, All limits at 95% CLmissT

h(bb) + EZ'-2HDM

= 100 GeVχ

= 0.8, mZ

= 1, gβtan = 300 GeV±H = mHm

New developments

8

•Object reconstruction ‣ variable-radius track-jets ‣ particle-flow jets + DNN-based b-tagger ‣ energy corrections for leptonic b-decays

•Analysis optimisation ‣more ETmiss bins in merged region ‣ new cuts that reduce background

contamination (jet vetoes, mtop, pT(bb)) ‣ inclusion of ≥3 b-jets

ATLAS-CONF-2018-039 ATLAS-CONF-2021-006

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

200400600800

1000120014001600180020002200

[GeV

]A

m/m > 20%Γ

Observed LimitExpected Limit

expσ1 ±

expσ2 ±arXiv:1903.01400

h + ma = m

Am

ATLAS Preliminary-1 = 13 TeV, 139 fbs

missT

h(bb) + EAll limits at 95% CL2HDM+a

= 1βggF production, tan = 10 GeVχ

= 0.35, mθsin±H = mH = mA = 1, m

χg

100 150 200 250 300 350 400 [GeV]am

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[GeV

]A

m

Observed LimitExpected Limit

expσ1 ±

expσ2 ±

h + ma = m

Am

ATLAS Preliminary-1 = 13 TeV, 139 fbs

missT

h(bb) + EAll limits at 95% CL2HDM+a

= 10βbbA production, tan = 10 GeVχ

= 0.35, mθsin±H = mH = mA = 1, m

χg

Interpretation

9

2HDM+a limits

• No excess observed • Can exclude

• 2HDM+a: mA ≲ 1.6 TeV, ma ≲ 500 GeV • Z’ 2HDM: mZ’ ≲ 3 TeV, mA ≲ 1 TeV

• New region with ≥ 3 b-jets allows to exclude b-associated production for the first time • Also derive limit on visible cross-section

gluon fusion , tanβ=1 b-associated production, tanβ=10

ATLAS-CONF-2021-006 ATLAS-CONF-2021-006

Displaced Higgs decays to b-quarks

Motivation

11

• Higgs decays to long-lived neutral scalars

• Mixing of scalars allows them to decay to SM particles

• Long-lived neutral scalars • proper decay length cτ : 10-6 - 107 m • favoured mass: 10 ≲ ms ≲ 60 GeV • mostly decaying to b-quarks for ms≳ 10 GeV

<latexit sha1_base64="FygsB1SnnJ+vIk0NLU4zoTm4oBw=">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</latexit>

L � �h

vs†s

︸displaced decay

DV

DV

Rept.Prog.Phys. 82 (2019) 11, 116201

State of the art

12

Searches with dedicated triggers • calorimeter: 0.1 ≲ cτ ≲ 10 m • muon system: cτ ≲ 100 m

Search in VH associated production • no displaced techniques: 50 μm ≲ cτ ≲ 2 mm

(updated results in talk by L. Morvaj)

Sensitivity gap in range cτ = 2-80 mm • decays inside inner detector ⇒ very hard to trigger

What we need • way to trigger: use leptons in ZH associated production • reconstruct displaced objects

JHEP 10 (2018) 031

Reconstruction of displaced objects

13

ATL-PHYS-PUB-2017-014

2. Large-radius tracking - loosen track-to-vertex association cuts and rerun

tracking algorithm using left-over hits ➡ 2-5 times higher efficiency than standard tracking

zPU vertex Primary vertex

1. Select events with displaced jet candidates - low charged hadron fraction - few tracks matched to primary vertex ➡ reduce events to be processed by costly algorithms

3. Displaced vertex reconstruction - run vertexing on large-radius tracks ➡ number of displaced vertices associated

to jets is the main analysis discriminant

Displaced vertex

Analysis

14

• Signal - SM Higgs forced to decay to scalars which further

decay to b-quarks - ma, τa : free parameters

• Event selection - lepton from Z used for triggering - require at least two jets - match displaced vertices to 4 leading b-jets - signal region: ≥ 2 displaced vertices - control region: < 2 displaced vertices to measure DV probability p(pTjet, b-tag score)

• Background estimation - number of background events in SR estimated from CR based on binomial probability - validated in γ + jet region

DV

DV

Results

15

Number of displaced vertices in signal region

Limits on branching ratio to long-lived scalars

• No events detected in signal region • Limits on BR(h→ss) cover range of 2-500 mm ✓ Most stringent limits to-date for ma < 40 GeV

ATLAS-CONF-2021-005

ATLAS-CONF-2021-005

16

Several ongoing searches/measurements probing the relation of the Higgs sector with the dark sector with complementary sensitivity.

Upcoming combinations expected to further increase the parameter space we can probe.

Maybe the Higgs boson will help us understand some of the properties of the dark Universe.

Baryogenesis

Dark

Matter

Dark Energy

Still a long but exciting road ahead…

Higgs to displaced b-quarks

ATLAS inner detector dimensions

19

Pileup dependence - large-radius tracking

20

ATL-PHYS-PUB-2017-014

✓ impact parameter resolution ~constant • reconstruction efficiency drops at high pile-up (under investigation)

Selection of displaced objects

21

• CHF peaks at ~0.6 for data, and close to 0 for signal • max αvertex used as discriminant: has a peak at 0 for signal, with a broad

distribution for jets in data • Filter:

• leading or sub-leading jets have: CHF < 0.045 or max αvertex < 0.05

• Displaced vertex reconstruction efficiency: 40-60% in for 5 < Lxy < 80 mm

Rejection of fake displaced vertices

22

Reject vertices whose (x,y,z) position coincides with known detector elementsGets rid of most SM backgrounds e.g. Ks → π+ π-

Tracker acceptance

Reduce bg due to random crossing of tracks in the vicinity of metastable hadron decay

DV probability

23

- Parametrised as a function of jet pT and b-tagging score

- Extracted from control region - High pT jets have higher track density ⇒

increased probability for DV - b-jets have hadrons that decay away from

primary vertex

- Uncertainty on DV probability is obtained from pseudoexperiments varying p(pT,DL1) within statistical uncertainties

ATLAS-CONF-2021-005

Background estimation

24

- Use probability map pDV(pT,DL1) - Binomial probability for having n displaced vertices in 4 leading jets:

- e.g. for exactly 1 DV: <latexit sha1_base64="P0wiBp3UIUQZ46X+pHnJka2GbAw=">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</latexit>

P (1 DV) =4X

i=1

pjet iDV (pT,i, DL1i)

Y

j 6=i

h1� pjet j

DV (pT,j , DL1j)i

<latexit sha1_base64="dLdy8Hg/aysMIgOQvp8jK4Ymino=">AAACH3icbVDJSgNBEO1xN25Rj14agxAPhpngdhFEPXgcwUQhM4SeTk1s0rPYXSOGIX/ixV/x4kER8Za/sbMc4vKg4dV7VVTXC1IpNNp235qanpmdm19YLCwtr6yuFdc36jrJFIcaT2SibgOmQYoYaihQwm2qgEWBhJugcz7wbx5AaZHE19hNwY9YOxah4AyN1CweumWvDfe06iE8Yu7Ri3pv98TZc8vOpGJqe7JuFkt2xR6C/iXOmJTIGG6z+OW1Ep5FECOXTOuGY6fo50yh4BJ6BS/TkDLeYW1oGBqzCLSfD+/r0R2jtGiYKPNipEN1ciJnkdbdKDCdEcM7/dsbiP95jQzDYz8XcZohxHy0KMwkxYQOwqItoYCj7BrCuBLmr5TfMcU4mkgLJgTn98l/Sb1acQ4q9tV+6fRsHMcC2SLbpEwcckROySVxSY1w8kReyBt5t56tV+vD+hy1TlnjmU3yA1b/G7o3oE8=</latexit>

P (� 2 DV) = 1� P (1 DV)� P (0 DV)

- Use above formula to estimate background events in signal region

Validation of background estimate

25

- Use γ + jet selection which has high statistics - At least 1γ with pT(γ) > 160 GeV or at least 2γ

with pT(γ) > 60 GeV & no offline leptons

- Estimate pDV(pT, DL1) in events with less than 2 DV and estimate background in region with nDV ≥ 2

- Data: 23 ± 5 events - MC: 19.9 ± 0.4 events

ATLAS-CONF-2021-005

ATLAS-CONF-2021-005

Uncertainties

26

Major systematics (~independent of ma/cτa) from: - Tracking (differences in LRT efficiency between data/MC - quantified using Ks → π+ π- decays) - Theory (VH cross-section/acceptance from scale/PDF/αs variation and parton shower) - LLP filter (filter uses uncalibrated jets - raise jet pT cut from 20 to 25 GeV and estimate change in filter

efficiency)

ATLAS-CONF-2021-005

Comparison with measurements

27

excluded from SM meas.

<latexit sha1_base64="yAUpEGB/oKlhlFxuMu7uGecpo6w=">AAACGXicbZBNS8NAEIY39bt+VT16CRbBU0lE0YsgetCLUNFqoWnLZLuxa3eTsDsRS8jf8OJf8eJBEY968t+4/UC09YWFh3dmmJ3XjwXX6DhfVm5icmp6ZnYuP7+wuLRcWFm90lGiKKvQSESq6oNmgoesghwFq8aKgfQFu/Y7x7369R1TmkfhJXZjVpdwE/KAU0BjNQuO14E4huZtY/vACxTQ1DsBKY2R/VAj9ZDdY3pxlmVZs1B0Sk5f9ji4QyiSocrNwofXimgiWYhUgNY114mxnoJCTgXL8l6iWQy0AzesZjAEyXQ97V+W2ZvGadlBpMwL0e67vydSkFp3pW86JWBbj9Z65n+1WoLBfj3lYZwgC+lgUZAIGyO7F5Pd4opRFF0DQBU3f7VpG0w+aMLMmxDc0ZPH4Wq75O6WnPOd4uHRMI5Zsk42yBZxyR45JKekTCqEkgfyRF7Iq/VoPVtv1vugNWcNZ9bIH1mf3wUvoZU=</latexit>

2j =

�j

�SMj

- Constraints on Higgs to undetected/invisible decays can be extracted from Higgs measurements using the coupling-modifiers framework

<latexit sha1_base64="KQea9j3H2P2SSoJj22EGEMS75Ns=">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</latexit>

2H(, Bi, Bu) =

PjBSM

j2j

1�Bi �Bu

- Extracting Bu requires additional assumptions, e.g. κZ,κW ≤ 1

- Depending on assumptions - Bu < 12% [1909.02845] - Bu < 19% [ATLAS-CONF-2020-027] - Binvisible+undedected ≲ 30% with latest data

ATLAS-CONF-2021-005

Comparison with CMS

28

- CMS uses different strategy [2012.01581]

- Dijet events - targeting ggF Higgs production which has 500x larger cross-section than VH

- Displaced jet trigger using HT

- No limit for decays to b-quarks for masses below 40 GeV!

Mono-Higgs to b-quarks

mH distributions (2 b-tag region)

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eV DataSM VhDibosonW+(bb,bc,cc,bl)W+(cl,l)tt

Single topZ+(bb,bc,cc,bl)Z+(cl,l)tth+ttVBackground Uncertainty

100)×Mono-h Z'-2HDM () = (1400,1000) GeV

A,m

Z'(m

= 1.89 fbsignalσ

ATLAS Preliminary -1 = 13 TeV, 139 fbs

Resolved: 0-lepton-tag Signal Regionb2

[150, 200) GeV∈ missTE

60 80 100 120 140 160 180 200 220 240 260 280 [GeV]bbm

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Single topZ+(bb,bc,cc,bl)Z+(cl,l)tth+ttVBackground Uncertainty

20)×Mono-h Z'-2HDM () = (1400,1000) GeV

A,m

Z'(m

= 1.89 fbsignalσ

ATLAS Preliminary -1 = 13 TeV, 139 fbs

Resolved: 0-lepton-tag Signal Regionb2

[200, 350) GeV∈ missTE

60 80 100 120 140 160 180 200 220 240 260 280 [GeV]bbm

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Single topZ+(bb,bc,cc,bl)Z+(cl,l)tth+ttVBackground Uncertainty

5)×Mono-h Z'-2HDM () = (1400,1000) GeV

A,m

Z'(m

= 1.89 fbsignalσ

ATLAS Preliminary -1 = 13 TeV, 139 fbs

Resolved: 0-lepton-tag Signal Regionb2

[350, 500) GeV∈ missTE

60 80 100 120 140 160 180 200 220 240 260 280 [GeV]bbm

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ATLAS-CONF-2021-006

mH distributions (3+ b-tag region)

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Single topZ+(bb,bc,cc,bl)Z+(cl,l)tth+ttVBackground Uncertainty

10)×Mono-h 2HDM+a () = (1000,150) GeVa,m

A(m

= 62.7 fbsignal

σ = 10, βtan

ATLAS Preliminary -1 = 13 TeV, 139 fbs

Resolved: 0-lepton-tag Signal Regionb3 ≥

[150, 200) GeV∈ missTE

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Single topZ+(bb,bc,cc,bl)Z+(cl,l)tth+ttVBackground Uncertainty

10)×Mono-h 2HDM+a () = (1000,150) GeVa,m

A(m

= 62.7 fbsignal

σ = 10, βtan

ATLAS Preliminary -1 = 13 TeV, 139 fbs

Resolved: 0-lepton-tag Signal Regionb3 ≥

[200, 350) GeV∈ missTE

60 80 100 120 140 160 180 200 220 240 260 280 [GeV]bbm

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SM VhDibosonW+(bb,bc,cc,bl)W+(cl,l)tt

Single topZ+(bb,bc,cc,bl)Z+(cl,l)tth+ttVBackground UncertaintyMono-h 2HDM+a

) = (1000,150) GeVa,mA

(m = 62.7 fb

signalσ = 10, βtan

ATLAS Preliminary -1 = 13 TeV, 139 fbs

Resolved: 0-lepton-tag Signal Regionb3 ≥

[350, 500) GeV∈ missTE

60 80 100 120 140 160 180 200 220 240 260 280 [GeV]bbm

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ATLAS-CONF-2021-006

ETmiss distributions

32

2 b-jets ≥ 3 b-jets

ATLAS-CONF-2021-006

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Single topZ+(bb,bc,cc,bl)Z+(cl,l)tth+ttVBackground Uncertainty

100)×Mono-h Z'-2HDM () = (1400,1000) GeV

A,m

Z'(m

= 1.89 fbsignalσ

ATLAS Preliminary -1 = 13 TeV, 139 fbs

Resolved: 0-lepton-tag Signal Regionb2

[150, 200) GeV∈ missTE

60 80 100 120 140 160 180 200 220 240 260 280 [GeV]bbm

0.81

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Limit on visible cross-section

33

- Merge bins in range mH=90-150 GeV in a single bin

- Insert 1 dummy signal event corresponding to a cross-section of 1 fb in each signal region

- Signal strengths are decorrelated in all signal regions

- Extract limit corresponding to

ATLAS-CONF-2021-006

Limit on visible cross-section

34

[150,200) GeV

∈missT

E [200,350) GeV

∈missT

E [350,500) GeV

∈missT

E [500,750) GeV

∈missT

E > 750 GeV

missTE

[150,200) GeV

∈missT

E [200,350) GeV

∈missT

E [350,500) GeV

∈missT

E > 500 GeV

missTE

1−10

1

10

[fb]

vis,

h+D

Mσ

upp

er li

mit

on

sCL

Observed LimitExpected Limit

expσ1 ±

expσ2 ±

ATLAS Preliminary-1 = 13 TeV, 139 fbs

, All limits at 95% CLmissT

h(bb) + E

-tagb2 -tagb3 ≥

ATLAS-CONF-2021-006

Uncertainties

35

- Statistically limited for high masses - At low masses main systematics arising from

- theory (Z+hf, ttbar cross-section) - Jet reconstruction

ATLAS-CONF-2021-006

Limit on 2HDM + Z’

36

- NB in previous iteration mH=mH±=300 GeV was used

- In the current iteration we use mH=mH±=mA

- This limits the possible A decays increasing the cross-section ⇒ higher exclusion

500 1000 1500 2000 2500 3000 3500 [GeV]Z'm

400

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[GeV

]A

m

Observed LimitExpected Limit

expσ1 ±

expσ2 ±

h -

mZ'

= m

A

Kin.

limit :

m

ATLAS Preliminary-1 = 13 TeV, 139 fbs

, All limits at 95% CLmissT

h(bb) + EZ'-2HDM

= 100 GeVχ

= 0.8, mZ

= 1, gβtan±H = mH = mAm

ATLAS-CONF-2021-006

Comparison with CMS

37

- Major difference: CMS generally uses mT(bb+ETmiss) instead of m(bb)

- ATLAS also has a search for V’ resonances (e.g. Z’→Z(vv)H(bb)) in the context of HVT models but no interpretation so far in the context of DM

JHEP 11 (2018) 172

Event selection - Mono-Higgs

38

Also used in previous iteration - Extended τ veto: remove events with Δφ(jet, ETmiss) < π/8 & track-multiplicity in jet is between 1-4 - reduce top + W+jets

- ETmiss significance - reduce events with fake ETmiss (multi-jet)

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S =|Emiss

T |p�2L(1� ⇢2LT )

New cuts - Top mass proxy variables used to reduce

top background

- Vetoing events with high jet multiplicity reduced top background further

- Cut on Higgs candidate pT reduces all bg

2HDM+Z’ constraints from other searches

39

plot by by Uli Haisch

2HDM+a ggF sensitivity at high mA

40

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gaah =1

Mhv

⇥(M2

h + 2M2A � 2M2

a � 2�3v2) sin2 ✓ � 2(�P1 cos

2 � + �P2 sin2 �)v2 cos2 ✓

⇤

=(M2

h + 2M2A � 2M2

a ) sin2 ✓ � 6v2

Mhv

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gAah =1

MAv

⇥M2

h+M2

H�M2

a� 2�3v

2 + 2(�P1 cos2 � + �P2 sin

2 �)v2⇤sin ✓ cos ✓

=(M2

A�M2

a+M2

h) sin ✓ cos ✓

MAv⇒ always positive

⇒ flips sign at mA = 1200 GeV (sinθ=0.35)

- The cross-section at high mA is completely dominated by the a→ah process, whose cross-section increases with mA ⇒ improved exclusion at high mA

thanks to Uli Haisch for providing the plot!