Search for 3rd generation superpartners with the ATLAS experiment - - PowerPoint PPT Presentation

SLIDE 1

DPF2017 July 31 (Fermilab)

Search for 3rd generation superpartners with the ATLAS experiment

Keisuke Yoshihara (University of Pennsylvania)

SLIDE 2

DPF2017, July31 2017, Keisuke Yoshihara (University of Pennsylvania)

Introduction

Λ: UV cut-off ~ Planck scale

h h h h λf s (scalar partner) λs

−m2

Z

2 = |µ2| + m2

Hu

˜ H

˜ tL

˜ bL ˜ tR

˜ g

stop mass (1-loop order) sparticle mass arXiv:1110.6926

• 1. Higgs mass divergence 


at Planck scale due to 
 radiative corrections 
 (Hierarchy problem)

• > t and b are a key 


(large Yukawa coupling)

• 2. Naturalness (Natural

SUSY) suggests the presence of light 3rd gen. squarks together with the higgsino LSP(s). The SM of particle physics is incomplete. Supersymmetry can be a new theory solving various problems remained in the SM.

~

2

~

SLIDE 3

DPF2017, July31 2017, Keisuke Yoshihara (University of Pennsylvania)

3 LHC was constructed to perform various searches (Higgs boson and BSM physics) at TeV energy scale.

Large Hadron Collider (LHC)

SLIDE 4

DPF2017, July31 2017, Keisuke Yoshihara (University of Pennsylvania)

4

Challenging environment at LHC

0.1 1 10 10

• 7

10

• 6

10

• 5

10

• 4

10

• 3

10

• 2

10

• 1

10 10

1

10

2

10

3

10

4

10

5

10

6

10

7

10

8

10

9

10

• 7

10

• 6

10

• 5

10

• 4

10

• 3

10

• 2

10

• 1

10 10

1

10

2

10

3

10

4

10

5

10

6

10

7

10

8

10

9

σ σ σ σZZ σ σ σ σWW σ σ σ σWH σ σ σ σVBF MH=125 GeV

HE LHC

WJS2012

σ σ σ σjet(ET

jet > 100 GeV)

σ σ σ σjet(ET

jet > √

√ √ √s/20) σ σ σ σggH

LHC Tevatron

events / sec for L = 10

33 cm

• 2s
• 1

σ σ σ σb σ σ σ σtot

proton - (anti)proton cross sections

σ σ σ σW σ σ σ σZ σ σ σ σt

σ σ σ σ ( ( ( (nb) ) ) ) √ √ √ √s (TeV)

{

mt ~1 TeV

MSTW 2008 NLO PDFs

• As the luminosity increases, number
• f interactions per crossing (pile-up
• r μ) and detector occupancy

increases.

• The cross section for the SUSY

is very small.

• Collecting important physics

events in this difficult environment is a key at the LHC.

20 pile-up 2 pile-up

~

SLIDE 5

DPF2017, July31 2017, Keisuke Yoshihara (University of Pennsylvania)

Not reviewed,

Basic Event topologies of SUSY!

˜ t , ˜ b

• The stop/sbottom is pair-produced (in RPC scenario) from the gg

process if the mass is light (mt,b < 1 TeV). As the SUSY mass goes high, the qq contribution gets larger (PDF is very steep).

• The stop/sbottom decays into intermediate states (χ20, χ1±) if exists,
• therwise the stop/sbottom decays directly into the LSP (χ10).

~ ~

~ ~

SUSY production and decay

g/q g/q q q g/q ~ ~ ~ ~

SUSY decay and production at LHC

~

5

SLIDE 6

DPF2017, July31 2017, Keisuke Yoshihara (University of Pennsylvania)

• Various pMSSM (or simplified) models are built to cover the various

physics models (GUT, Naturalness, etc…) and the LSP scenarios.

• The event selection is optimized for the various final states, 


e.g. t -> tχ10, bχ1±, b -> bχ10, tχ1± …

• Both RPC and RPV stop/sbottom searches are performed in ATLAS.

This talk focuses on RPC scenario.

1, ˜

χ±

1 , ˜

χ0

2, 1, ˜

χ0

1, 1, ˜

χ±

1 , ˜

χ0

2, ˜

χ0

3

˜ t1, ˜ t1,

1, ˜

χ0

1, 1, ˜

χ0

1, 1, ˜

χ0

1, ˜

χ±

1 , ˜

χ0

2,

˜ t1,˜ b1, ˜ t1, (˜ b1)

a) pure bino LSPP b) wino NLSP P c) higgsino LSP P d) bino/higgsino mix

sparticle masses

~ ~ ~ ~

6

Search strategy

SLIDE 7 1, ˜

χ±

1 , ˜

χ0

2, 1, ˜

χ0

1,

˜ t1,˜ b1,

b) Wino NLSP

Sparticle masses

˜ t ˜ t ˜ χ±

1

˜ χ⌥

1

p p b ˜ χ0

1

W b ˜ χ0

1

W

b + χ1±

˜ t1 ˜ t1 ˜ χ0

2

˜ χ0

2

p p t ˜ χ0

1

h t ˜ χ0

1

Z

t + χ20

a) Pure Bino LSP

1, ˜

χ0

1,

˜ t1, Sparticle masses

t + χ10

˜ t1 → bff 0 ˜ χ0

1

˜ t1 → bW ˜ χ0

1

˜ t

1

→ t ˜ χ

1

∆ m > ∆ m > m˜

t1

∆ m > mW + mb ∆ m > ∆ m > m˜

t

m > mW +

∆m = m˜

t1 − m˜ χ0 1

0 100 200 300 100 200 0 100

˜ t1 → c˜ χ0

1

∆ m > m

t

m˜

t1 < m˜ χ0 1

] m˜

t1 [GeV]

] m˜

χ0 1 [GeV]

Decay is governed by Δm(t1,χ10). b+χ1± signature:
 high pT b-jets, jets, and large MET Wino NLSP (m(χ1±)~ 2m(χ10)) (pMSSM) model: GUT (cMSSM/mSUGRA) Pure bino LSP (simplified) model: New technique: 
 BDT and shape-fit

DPF2017, July31 2017, Keisuke Yoshihara (University of Pennsylvania)

~ ~

~ ~ ~

~

7

Bino LSP models

~ ~

SLIDE 8

c) Higgsino LSP

˜ t1,

1, ˜

χ0

1, ˜

χ±

1 , ˜

χ0

2,

Sparticle masses

Higgsino LSP (simplified) model: Naturalness

d) Bino/Higgsino mix

1, ˜

χ±

1 , ˜

χ0

2, ˜

χ0

3 1, ˜

χ0

1,

˜ t1, (˜ b1)

Sparticle masses

Signature:
 Soft-objects and large MET Two benchmark models: a) Δm(χ10,χ1±) = 5 GeV b) variable Δm(χ10,χ1±) = 0-30 GeV

[GeV]

T

lepton p 5 10 15 20 25 30

Data / SM

0.5 1 1.5

Events / 1 GeV 100 200 300 400 500

Data Total SM 2L t t 1L t t W+jets Single top +V t t Diboson ATLAS Preliminary

• 1

= 13 TeV, 36.1 fb s Preselection (soft lepton)

DPF2017, July31 2017, Keisuke Yoshihara (University of Pennsylvania)

• Admixture LSP (bino/higgsino) satisfying M1 ~ -|µ|
• Typical Δm(χ10,χ1±) ~ 20-50 GeV
• Interpretation only (no event selection optimized)

Well-tempered (pMSSM) model: DM relic density (Ωh2 ~ 1.12) ~ ~ ~ ~

8

Higgsino LSP models

~ ~ ATLAS-CONF-2017-037

SLIDE 9

DPF2017, July31 2017, Keisuke Yoshihara (University of Pennsylvania)

9

Top quark reconstruction

• In the decay of heavy stop, the top quark is highly
• boosted. As a consequence jets from the top decay

tends to form a large radius jet.

t q q b Boosted top

R=1.0

t b q q Resolved top

[GeV]

reclustered top

m 100 150 200 250 300 350

Data / SM

0.5 1 1.5

Events / 10 GeV

2

10

3

10

4

10

Data Total SM 2L t t 1L t t Single top W+jets Others ATLAS Preliminary

• 1

= 13 TeV, 36.1 fb s )

miss T

Preselection (high E

Events / 20 GeV

• The analysis benefits from reconstructing hadronically

decaying top quark (“hadronic top reconstruction”).

ATLAS-CONF-2017-037

SLIDE 10

DPF2017, July31 2017, Keisuke Yoshihara (University of Pennsylvania)

10

Background estimate

• Use control region (invert one or two SR selections)
• Simulation uncertainties (PS+hadronization, hard-

scattering, PDF, …) need to be assessed and propagated when extrapolating the norm to the SR.

• Minor backgrounds are normalized to the SM prediction.

[GeV]

(ll) T

p 100 200 300 400 500 600

Data / SM

0.5 1 1.5

Events / 40 GeV 5 10 15 20 25 30

Data Total SM +V t t Diboson Single top Others ATLAS Preliminary

• 1

= 13 TeV, 36.1 fb s tN_med ttZ CR

Variable A Variable B CR SR

ttZ(ll) CR

pT of Z(ll) [GeV] ATLAS-CONF-2017-037

SLIDE 11

DPF2017, July31 2017, Keisuke Yoshihara (University of Pennsylvania)

11

Results: Validation region

0.077 0.154 0.231 0.308 0.385 0.462 0.538 0.615 0.692 0.769 0.846 0.923 1

Events

1 10

2

10

3

10

Data Total SM 2L t t 1L t t W+jets +V t t Single top Diboson

Signal regions

ATLAS Preliminary

• 1

= 13 TeV, 36.1 fb s

bffN TVR bffN WVR bWN TVR tN_med T1LVR tN_med T2LVR tN_med WVR tN_high T1LVR tN_high T2LVR tN_high WVR bffN bWN tN_med tN_high

tot

σ ) /

exp

• n
• bs

(n 2 − 2

Blinded SR

• VRs are monitored while blinding SRs.

Validation Regions

ATLAS-CONF-2017-037

SLIDE 12

DPF2017, July31 2017, Keisuke Yoshihara (University of Pennsylvania)

12

Results: Signal region

0.077 0.154 0.231 0.308 0.385 0.462 0.538 0.615 0.692 0.769 0.846 0.923 1

Events

1 10

2

10

3

10

Data Total SM 2L t t 1L t t W+jets +V t t Single top Diboson

Signal regions

ATLAS Preliminary

• 1

= 13 TeV, 36.1 fb s

bffN TVR bffN WVR bWN TVR tN_med T1LVR tN_med T2LVR tN_med WVR tN_high T1LVR tN_high T2LVR tN_high WVR bffN bWN tN_med tN_high

tot

σ ) /

exp

• n
• bs

(n 2 − 2

• No significant excess is observed.

Validation Regions

ATLAS-CONF-2017-037

Signal Region

SLIDE 13

13

Results: Pure Bino LSP

[GeV]

1

t ~

m

200 300 400 500 600 700 800 900 1000

[GeV]

1

χ ∼

m

100 200 300 400 500 600 700

1

χ ∼ W b →

1

t ~ /

1

χ ∼ t →

1

t ~

1

χ ∼ b f f' →

1

t ~ /

1

χ ∼ W b →

1

t ~ /

1

χ ∼ t →

1

t ~

1

χ ∼ b f f' →

1

t ~ /

1

χ ∼ W b →

1

t ~ /

1

χ ∼ t →

1

t ~

1

χ ∼ c →

1

t ~

• 1

=8 TeV, 20 fb s

t

) < m

1

χ ∼ ,

1

t ~ m( ∆

W

+ m

b

) < m

1

χ ∼ ,

1

t ~ m( ∆ ) < 0

1

χ ∼ ,

1

t ~ m( ∆

1

χ ∼ t →

1

t ~ /

1

χ ∼ W b →

1

t ~ /

1

χ ∼ c →

1

t ~ /

1

χ ∼ b f f' →

1

t ~ production,

1

t ~

1

t ~

Status: May 2017

ATLAS Preliminary

1

χ ∼ W b

1

χ ∼ c

1

χ ∼ b f f'

Observed limits Expected limits All limits at 95% CL

=13 TeV s [CONF-2017-020]

• 1

0L 36.1 fb [CONF-2017-037]

• 1

1L 36.1 fb [CONF-2017-034]

• 1

2L 36.1 fb [1604.07773]

• 1

Monojet 3.2 fb Run 1 [1506.08616]

Since there’s no significant data excess, exclusion limits are set on t1 and χ10 masses.

a) Pure Bino LSP

1, ˜

χ0

1,

˜ t1,

Sparticle masses

ATLAS-CONF-2017-034 ATLAS-CONF-2017-037 ATLAS-CONF-2017-020

~ ~

DPF2017, July31 2017, Keisuke Yoshihara (University of Pennsylvania)

SLIDE 14

DPF2017, July31 2017, Keisuke Yoshihara (University of Pennsylvania)

14

Results: Wino NLSP

[GeV]

1

t ~

m 550 600 650 700 750 800 850 900 950 [GeV]

1

χ ∼

m 100 200 300 400 500 600

± 1

χ ∼

+ m

b

m <

t ~

m

)

1

M

×

= 2

2

M (

1

χ ∼

m

×

2 ≈

2

χ ∼

m ≈

± 1

χ ∼

m production,

1

b ~

1

b ~ ,

1

t ~

1

t ~ Wino NLSP model:

1

t ~ →

1,2

χ ∼ , t

± 1

χ ∼ b

1

b ~ →

1,2

χ ∼ , b

± 1

χ ∼ t

1

χ ∼ W →

± 1

χ ∼ <0: µ

1

χ ∼ , h

1

χ ∼ Z →

2

χ ∼ >0: µ

1

χ ∼ (dominant), Z

1

χ ∼ h →

2

χ ∼

= 600 GeV

1 b ~

m = 700 GeV

1 b ~

m = 800 GeV

1 b ~

m = 900 GeV

1 b ~

m

Observed limit )

exp

σ 1 ± Expected limit ( <0 µ >0 µ

ATLAS Preliminary

• 1

= 13 TeV, 36.1 fb s Limit at 95% CL

stop 1-lepton

Wino NLSP model (pMSSM) with the mass assumption m(χ1±) ~ 2m(χ10) . Two contours correspond to μ > 0 and μ < 0.

1, ˜

χ±

1 , ˜

χ0

2, 1, ˜

χ0

1,

˜ t1,˜ b1,

b) Wino NLSP

Sparticle masses

) [GeV]

1

t ~ m( 550 600 650 700 750 800 850 900 ) [GeV]

1

χ ∼ m( 100 150 200 250 300 350 400 450 500

(800 GeV) 1 b ~ (700 GeV) 1 b ~ (600 GeV) 1 b ~ 1,2

χ ∼ , t

± 1

χ ∼ b → t ~

1,2

χ ∼ , b

± 1

χ ∼ t → b ~

1

χ ∼ W →

± 1

χ ∼

1

χ ∼ , Z

1

χ ∼ h →

2

χ ∼ <0; µ

1

χ ∼ (dominant), Z

1

χ ∼ h →

2

χ ∼ >0; µ

b

+ m

± 1 χ ∼

) < m

1 χ ∼

, m

1 t ~

m ( m ∆

)

1

= 2 x M

2

, (M

1

χ ∼

2 x m ≈

± 1

χ ∼

production, m

1

b ~

1

b ~ ,

1

t ~

1

t ~

• 1

= 13 TeV, 36.1 fb s ATLAS Preliminary

<0 µ )

exp

σ 1 ± Expected limit ( >0 µ )

exp

σ 1 ± Expected limit ( <0 µ Observed limit >0 µ Observed limit

~ ~

stop 2-lepton

SLIDE 15

c) Higgsino LSP

˜ t1,

1, ˜

χ0

1, ˜

χ±

1 , ˜

χ0

2,

DPF2017, July31 2017, Keisuke Yoshihara (University of Pennsylvania)

15

Results: Higgsino LSP

Higgsino LSP model (pMSSM-inspired simplified model) with the assumption Δm(χ10, χ20) ~ 2Δm(χ10, χ1±) . Three contours correspond to t1 ~ tR and t1 ~ tL (w/ large tanβ).

Sparticle masses

~ ~

[GeV]

1

t ~

m 600 700 800 900 1000 1100 1200 1300 1400 ) [GeV]

1

χ ∼ ,

± 1

χ ∼ m( ∆ 5 10 15 20 25 30

= 150 GeV

± 1

χ ∼

m production,

1

t ~

1

t ~ Higgsino LSP model:

1

t ~ →

1,2

χ ∼ , t

± 1

χ ∼ b

1

χ ∼ W →

± 1

χ ∼

1

χ ∼ , Z

1

χ ∼ h →

2

χ ∼ ≈ )

1

χ ∼ , t

± 1

χ ∼ , b

2

χ ∼ BR(t : (45, 10, 45)% β , small tan

L

t ~ : (33, 33, 33)% β , large tan

L

t ~ : (25, 50, 25)%

R

t ~

Observed limit )

exp

σ 1 ± Expected limit (

L

t ~ ≈

1

t ~

R

t ~ ≈

1

t ~ ) β (large tan

L

t ~ ≈

1

t ~

ATLAS Preliminary

• 1

= 13 TeV, 36.1 fb s Limit at 95% CL

stop 1-lepton

~ ~ ~ ~ ~ ~

SLIDE 16

DPF2017, July31 2017, Keisuke Yoshihara (University of Pennsylvania)

16

Results: Well-tempered LSP

Sparticle masses

[GeV]

1

t ~

m 500 600 700 800 900 [GeV]

1

χ ∼

m 200 300 400 500 600

) = 20-50 GeV

1

χ ∼ ,

2

χ ∼ m( ∆ production,

1

b ~

1

b ~ +

1

t ~

1

t ~ Bino/Higgsino mix model:

1

t ~ →

1,2,3

χ ∼ , t

± 1

χ ∼ b

1

b ~ →

1,2,3

χ ∼ , b

± 1

χ ∼ t

1,2

χ ∼ W* →

± 1

χ ∼

1,2

χ ∼ , Z*/h*

± 1

χ ∼ W* →

3

χ ∼

1

χ ∼ Z*/h* →

2

χ ∼

Observed limit )

exp

σ 1 ± Expected limit (

L

t ~ ≈

1

t ~

R

t ~ ≈

1

t ~

ATLAS Preliminary

• 1

= 13 TeV, 36.1 fb s Limit at 95% CL

stop 1-lepton

d) Bino/Higgsino mix

1, ˜

χ±

1 , ˜

χ0

2, ˜

χ0

3 1, ˜

χ0

1,

˜ t1, (˜ b1)

Admixture LSP model (pMSSM) with the assumption 
 M1 ~ -|µ| while satisfying DM relic density Ωh2 ~ 1.12. 
 Two contours correspond to t1 ~ tR and t1 ~ tL.

~ ~ ~ ~

SLIDE 17

DPF2017, July31 2017, Keisuke Yoshihara (University of Pennsylvania)

17

Sbottom search:

• A dedicated sbottom search 


(b -> bχ10/tχ1±) with 2b-quark and large MET final state.

• Z+jets is a main background

estimated by the data-driven method.

~

[GeV]

1

b ~

m 200 400 600 800 1000 1200 [GeV]

1

χ ∼

m 100 200 300 400 500 600 700 800 900 1000

1

χ ∼ b →

1

b ~ Bottom squark pair production,

• 1

=13 TeV, 36.1 fb s

Preliminary ATLAS

Best b0L SR

=8 TeV s ,

• 1

+ 2 b-jets, 20.1 fb T miss ATLAS E =13 TeV s ,

• 1

+ 2 b-jets, 3.2 fb T miss ATLAS E

)

theory SUSY

σ 1 ± Observed limit ( )

exp

σ 1 ± Expected limit (

forbidden

1

χ ∼ b →

1

b ~

[GeV]

1

b ~

m 200 300 400 500 600 700 800 900 1000 [GeV]

1

χ ∼

m 100 200 300 400 500 600 700 800

at 50% BR

+ 1

χ ∼ / t

1

χ ∼ b →

1

b ~ Bottom squark pair production,

• 1

=13 TeV, 36.1 fb s

Preliminary ATLAS

Best combined SR

=8 TeV s ,

• 1

+ 2b, 20.1 fb T miss ATLAS 1L + E Best b0L limits (exp) Best b0L limits (obs) Best b1L limits (exp) Best b1L limits (obs)

)

theory SUSY

σ 1 ± Observed limit ( )

exp

σ 1 ± Expected limit (

f

• r

b i d d e n

+ 1

χ ∼ t →

1

b ~

/χ1± /χ1± /t /t

~ ~

ATLAS-CONF-2017-038

~ ~

SLIDE 18

LHCP2017, May17 2017, Keisuke Yoshihara (University of Pennsylvania)

• Many new results from ATLAS for 3rd generation

squark searches are presented based on full 2015+2016 data (36 fb-1).

[GeV]

1

t ~

m

200 300 400 500 600 700 800 900 1000

[GeV]

1

χ ∼

m

100 200 300 400 500 600 700

1

χ ∼ W b →

1

t ~ /

1

χ ∼ t →

1

t ~

1

χ ∼ b f f' →

1

t ~ /

1

χ ∼ W b →

1

t ~ /

1

χ ∼ t →

1

t ~

1

χ ∼ b f f' →

1

t ~ /

1

χ ∼ W b →

1

t ~ /

1

χ ∼ t →

1

t ~

1

χ ∼ c →

1

t ~

• 1

=8 TeV, 20 fb s

t

) < m

1

χ ∼ ,

1

t ~ m( ∆

W

+ m

b

) < m

1

χ ∼ ,

1

t ~ m( ∆ ) < 0

1

χ ∼ ,

1

t ~ m( ∆

1

χ ∼ t →

1

t ~ /

1

χ ∼ W b →

1

t ~ /

1

χ ∼ c →

1

t ~ /

1

χ ∼ b f f' →

1

t ~ production,

1

t ~

1

t ~

Status: May 2017

ATLAS Preliminary

1

χ ∼ W b

1

χ ∼ c

1

χ ∼ b f f'

Observed limits Expected limits All limits at 95% CL

=13 TeV s [CONF-2017-020]

• 1

0L 36.1 fb [CONF-2017-037]

• 1

1L 36.1 fb [CONF-2017-034]

• 1

2L 36.1 fb [1604.07773]

• 1

Monojet 3.2 fb Run 1 [1506.08616]

• No significant

excesses this time around…

• Stringent constraints
• btained on various

pMSSM and simplified models. 18

Conclusion

SLIDE 19

Backup

19

SLIDE 20

DPF2017, July31 2017, Keisuke Yoshihara (University of Pennsylvania)

20

ATLAS detector

25m 46m

Muon HadCalo EMCalo Toroid and solenoid Trackers

• ATLAS is a multipurpose detector

composed of:

• inner trackers
• solenoid magnet
• calorimeters
• spectrometer (and toroid)
• Inner detector composed of Pixel, SCT,

and TRT, plays a key role in track reconstruction in the dense environment.

• Calorimeter composed of EM and

Hadronic calo, measures energy deposit of e/gamma and hadrons.

• Spectrometer reconstructs muons.

ATLAS Inner detector

SLIDE 21

1 2 5 10 20 50 100 105 110 115 120 125 130 135 MS @TeVD mh @GeVD

Naively squark mass scale (MS) is ~10 TeV.

no mixing (Xt = 0)

But the scalar top quark (stop) is special, one can make the stop mass much lighter, < 1 TeV with large tR - tL mixing (Xt = √6 mt). -> My current research

~

arXiv:1112.3068

~ ~

arXiv:1112.2703 Higgs boson mass [GeV]

stop mass [GeV] Ms [TeV]

Higgs boson mass [GeV]

What does the Higgs mass of 125GeV indicate?

21

SLIDE 22

DPF2017, July31 2017, Keisuke Yoshihara (University of Pennsylvania)

22

⇠

Scenario Wino NLSP Higgsino LSP Bino/higgsino mix Models pMSSM simplified pMSSM Mixing parameters Xt/MS ⇠ p 6 tan β 20 20 or 60 20 MS [TeV] 0.9-1.2 1.2 0.7-1.3 M3 [TeV] 2.2 2.2 1.8 Scanned mass parameters (M1, mq3L) (µ, mq3L/mtR) (M1,mq3L/mtR) Electroweakino masses [TeV] µ = ±3.0 M2 = M1 = 1.5 M2 = 2.0 M2 = 2M1 ⌧ |µ| µ ⌧ M1 = M2 M1 ⇠ µ, M1 < M2 Additional requirements – – 0.10 < Ωh2 < 0.12 – – ∆ < 100 Sbottom pair production considered – considered ˜ t1 decay modes and their BR [%] ˜ t1 ⇠ ˜ tL (a) / (b) / (c) (a) / (b) ˜ t1 ! t ˜ χ0

1

< 5 ⇠ 25/⇠ 45/⇠ 33 < 10/< 10 ˜ t1 ! b ˜ χ±

1

⇠ 65 ⇠ 50/⇠ 10/⇠ 33 ⇠ 50/⇠ 10 ˜ t1 ! t ˜ χ0

2

⇠ 30 ⇠ 25/⇠ 45/⇠ 33 ⇠ 20/⇠ 40 ˜ t1 ! t ˜ χ0

3

– – ⇠ 20/⇠ 40 ˜ b1decay modes and their BR [%] ˜ b1 ⇠ ˜ tL – ˜ b1 ⇠ ˜ bL ˜ b1 ! b ˜ χ0

1

< 5 – < 5 ˜ b1 ! t ˜ χ±

1

⇠ 65 – ⇠ 85 ˜ b1 ! b ˜ χ0

2

⇠ 30 – < 5 ˜ b1 ! b ˜ χ0

3

– – < 5

pMSSM model parameters

SLIDE 23

• Had top reconstruction: 


a key discriminant in stop1-lepton (t+χ10).

• Various MT2 variables (aMT2 or MT2ll ):


discriminating signal from ttbar events. Mass of hadronic top-quark

• Super-razor variables: [arXiv:13104827]


kinematic variables defined in super-razor (approximate boost) frame.

[GeV]

reclustered top

m 100 150 200 250 300 350

Data / SM

0.5 1 1.5

Events / 10 GeV

2

10

3

10

4

10

Data Total SM 2L t t 1L t t Single top W+jets Others

ATLAS Preliminary

• 1

= 13 TeV, 36.1 fb s )

miss T

Preselection (high E

Events / 20 GeV

Events / 0.02

1 −

10 1 10

2

10

3

10

4

10

t t Wt VV +V t t *+jets γ Z/ Others Data Standard Model

ATLAS Preliminary

• 1

= 13 TeV, 36.1 fb s 3-body selection

3-body t t

CR

T

p

R

0.7 0.75 0.8 0.85 0.9 0.95 1

Data / SM

0.5 1 1.5 2

Super-razor variable (RpT)

RpT = | ~ JT| | ~ JT| + √ ˆ sR/4 , DPF2017, July31 2017, Keisuke Yoshihara (University of Pennsylvania)

23

Discriminating variables

SLIDE 24

• Additional discriminating variables (e.g. RJ Rec: [arXiv:1607.08307]) for the

BDTs targeting the compressed t+χ10 region.

[GeV]

t,had

• based m

2

χ 100 150 200 250 300 350

Signal / SM

0.05 0.1 0.15

Data / SM

0.5 1 1.5

Events / 10 GeV 1000 2000 3000 4000 5000

Data Total SM 2L t t 1L t t W+jets Others

5 × σ )=250,62 GeV

1

χ ∼ ,

1

t ~ m(

ATLAS Preliminary

• 1

= 13 TeV, 36.1 fb s )

miss T

Preselection (low E

[GeV]

S T

M 100 200 300 400 500 600 700 800

Signal / SM

0.05 0.1 0.15 0.2

Data / SM

0.5 1 1.5

Events / 50 GeV 100 200 300 400 500

Data Total SM 2L t t 1L t t Single top W+jets Others

9 × σ )=(450,277) GeV

1

χ ∼ , t ~ m(

ATLAS Preliminary

• 1

= 13 TeV, 36.1 fb s )

miss T

Preselection (high E

Events / 0.04 Events / 0.076

RJR variable: MTS χ2-based hadronic top rec

DPF2017, July31 2017, Keisuke Yoshihara (University of Pennsylvania)

24

Discriminating variables for BDT

SLIDE 25

LHCP2017, May17 2017, Keisuke Yoshihara (University of Pennsylvania)

BDT_low 1 − 0.8 − 0.6 − 0.4 − 0.2 − 0.2 0.4 0.6 0.8 1

tot

σ ) /

exp

• n
• bs

(n 1 − 1

Events 10

2

10

3

10

4

10

5

10

) = (190,17) GeV

1

χ ∼ ,

1

t ~ m( ) = (250,77) GeV

1

χ ∼ ,

1

t ~ m(

Data Total SM 2L t t 1L t t W+jets Single top Diboson +V t t ATLAS Preliminary

• 1

= 13 TeV, 36.1 fb s tN_diag_low

BDT_med 1 − 0.8 − 0.6 − 0.4 − 0.2 − 0.2 0.4 0.6 0.8 1

tot

σ ) /

exp

• n
• bs

(n 1 − 1

Events 10

2

10

3

10

4

10

5

10

6

10

7

10

8

10 Data Total SM 2L t t 1L t t +V t t W+jets Single top Diboson

)=(250,62) GeV

1

χ ∼ ,

1

t ~ m( ATLAS Preliminary

• 1

= 13 TeV, 36.1 fb s tN_diag_med

BDT_high 1 − 0.8 − 0.6 − 0.4 − 0.2 − 0.2 0.4 0.6 0.8 1

tot

σ ) /

exp

• n
• bs

(n 1 − 1

Events 10

2

10

3

10

4

10

5

10 Data Total SM t t +V t t W+jets Single top Diboson

) = (450,277) GeV

1

χ ∼ ,

1

t ~ m( ATLAS Preliminary

• 1

= 13 TeV, 36.1 fb s BDT_high

Results: Pure Bino LSP scenario (BDT)

25

SLIDE 26

LHCP2017, May17 2017, Keisuke Yoshihara (University of Pennsylvania)

[GeV]

1

t ~

m 200 250 300 350 400 450 ) [GeV]

1

χ ∼ ,

1

t ~ m( ∆ 20 40 60 80 100 120 140 160 180 200

tN bWN bff'N

1

χ ∼ t →

1

t ~ ,

1

χ ∼ bW →

1

t ~ ,

1

χ ∼ bff' →

1

t ~ production,

1

t ~

1

t ~ Pure Bino LSP model:

)

th

σ 1 ± Observed limit ( )

exp

σ 1 ± Expected limit (

• 1

ATLAS 8 TeV, 20.3 fb

ATLAS Preliminary

• 1

= 13 TeV, 36.1 fb s Limit at 95% CL

26

Results: Pure Bino LSP scenario (Low mass zoom)

SLIDE 27

LHCP2017, May17 2017, Keisuke Yoshihara (University of Pennsylvania)

[GeV]

1

t ~

m 200 400 600 800 1000 1200 [GeV]

1

χ ∼

m 100 200 300 400 500 600 700

t ) < m 1 χ ∼ , 1 t ~ m( ∆ W +m b ) < m 1 χ ∼ , 1 t ~ m( ∆ ) < 0 1 χ ∼ , 1 t ~ m( ∆

1

χ ∼ t →

1

t ~ ,

1

χ ∼ Wb →

1

t ~ ,

1

χ ∼ bff' →

1

t ~ production,

1

t ~

1

t ~ Pure Bino LSP model:

tN_diag_low tN_diag_med tN_diag_high bffN bWN tN_med tN_high Observed limit Expected limit

ATLAS Preliminary

• 1

= 13 TeV, 36.1 fb s

) [GeV]

1

t ~ m( 100 200 300 400 500 600 700 800 ) [GeV]

1

χ ∼ m( 100 200 300 400 500 600

140 2-body

SRB

110 2-body

SRC

3-body

SR

4-body

SR

ATLAS Preliminary

stop 1-lepton stop 2-lepton

Results: Pure Bino LSP scenario (SR map)

27

SLIDE 28

LHCP2017, May17 2017, Keisuke Yoshihara (University of Pennsylvania)

[GeV]

1

t ~

m 400 500 600 700 800 900 1000 [GeV]

1

χ ∼

m 100 150 200 250 300 350 400

1

χ ∼

+ m

t

m <

t ~

m

+10 GeV

1

χ ∼

= m

2

χ ∼

m +5 GeV,

1

χ ∼

= m

± 1

χ ∼

m production,

1

t ~

1

t ~ Higgsino LSP model:

1

t ~ →

1,2

χ ∼ , t

± 1

χ ∼ b

1

χ ∼ W →

± 1

χ ∼

1

χ ∼ , Z

1

χ ∼ h →

2

χ ∼ ≈ )

1

χ ∼ , t

± 1

χ ∼ , b

2

χ ∼ BR(t : (45, 10, 45)% β , small tan

L

t ~ : (33, 33, 33)% β , large tan

L

t ~ : (25, 50, 25)%

R

t ~

Observed limit )

exp

σ 1 ± Expected limit (

L

t ~ ≈

1

t ~ ) β (large tan

L

t ~ ≈

1

t ~

R

t ~ ≈

1

t ~

ATLAS Preliminary

• 1

= 13 TeV, 36.1 fb s Limit at 95% CL

28

Results: Higgsino LSP fixed Δm=5GeV

SLIDE 29

LHCP2017, May17 2017, Keisuke Yoshihara (University of Pennsylvania)

[GeV]

1

t ~

m 200 250 300 350 400 450 500 550 [GeV]

1

χ ∼

m 100 150 200 250 300 350 400 450 500 550 600

)

1

χ ∼

= 5 GeV + m

1 ±

χ ∼

( m

1 ±

χ ∼

+m

b

< m

1

t ~

m

1

χ ∼

+m

t

> m

1

t ~

m

) = 100%

± 1

χ ∼ b →

1

t ~ production, BR(

1

t ~

1

t ~ Higgsino LSP model:

)

th

σ 1 ± Observed limit ( )

exp

σ 1 ± Expected limit (

ATLAS Preliminary

• 1

= 13 TeV, 36.1 fb s Limit at 95% CL

29

Results: Higgsino LSP diagonal region

SLIDE 30

• Spin-0 mediator model is studied, exploiting the similarity of

the final state: ttbar+MET (1-lepton).

• There *was* mild excess in DM_low(_loose) in 13.2 fb-1
• No longer significant with full 2015+2016 data (1.5σ).

0.714 0.7620.810.857

Z+jets

WVR_bCbv SR1 tN_high DM_low DM_high

(ATL-CONF-2016-050) 13.2fb-1

φ/a ¯ t t g g ¯ χ χ

0.091 0.182 0.273 0.364 0.455 0.545 0.636 0.727 0.818 0.909 1

Events

1 10

2

10

3

10

Data Total SM 2L t t 1L t t W+jets +V t t Single top Diboson

Signal regions

ATLAS Preliminary

• 1

= 13 TeV, 36.1 fb s

loose DM_low TVR loose DM_low WVR DM_low T1LVR DM_low T2LVR DM_low WVR DM_high T1LVR DM_high T2LVR DM_high WVR loose DM_low DM_low DM_high

tot

σ ) /

exp

• n
• bs

(n 2 − 2

3.3σ

stop 1-lepton

DPF2017, July31 2017, Keisuke Yoshihara (University of Pennsylvania)

Results: Spin-0 mediator model (DM+ttbar)

30

SLIDE 31

) [GeV] t ~ m( 600 800 1000 1200 1400 ) [GeV]

1

χ ∼ m( 500 1000 1500

• 1

= 13 TeV, 36.1 fb s

LSP H ~ ),

theory SUSY

σ 1 ±

• Obs. limit (

LSP H ~ ),

exp

σ 1 ±

• Exp. limit (

LSP B ~ ),

theory SUSY

σ 1 ±

• Obs. limit (

LSP B ~ ),

exp

σ 1 ±

• Exp. limit (

1 +

χ ∼ / b

1,2

χ ∼ t → t ~ s b b →

1 +

χ ∼ tbs, →

1,2

χ ∼

)

1

χ ∼ m ( t ) + m ( ≤ ) t ~ m (

All limits at 95% CL

ATLAS

LHCP2017, May17 2017, Keisuke Yoshihara (University of Pennsylvania)

˜ t ˜ t∗ ˜ χ0

1,2

˜ χ−

1

p p t

λ00

323

t b s ¯ b

λ00

323

b b s

• In RPV models, LSP decays further into

quarks, leading to multijets (up to >= 12 jets!) and a lepton (from semi-leptonic top- quark decay) final state.

• mt1 up to 1250 GeV (1100 GeV)

is excluded for the bino LSP (higgsino LSP) scenario.

• Higgsino LSP (with t1 ~ tR) and

Bino LSP scenarios considered.

RPV stop 1L search

31

SLIDE 32

LHCP2017, May17 2017, Keisuke Yoshihara (University of Pennsylvania)

) [GeV]

1

t ~ m( 400 500 600 700 800 900 ) [GeV]

1

χ ∼ m( 100 200 300 400 500 600 700

+ 10 GeV

± 1

χ ∼

= m

1

t ~

, m

± 1

χ ∼ b + →

1

t ~ production,

1

t ~

1

t ~

• 1

= 13 TeV, 36.1 fb s All limits at 95% CL ATLAS Preliminary

) = 10 GeV)

± 1 χ ∼

,m

1 t ~

m (m ∆ (

1 χ ∼

< m

± 1 χ ∼

m

)

exp

σ 1 ± Expected limit ( )

theory

σ 1 ± Observed limit (

• 1

= 8 TeV, 20 fb s

[GeV]

1

t ~

m 300 400 500 600 700 800 900 [GeV]

1

χ ∼

m 100 200 300 400 500 600 700

1 χ ∼

< m

± 1 χ ∼

m

)=10 GeV

± 1

χ ∼ ,

1

t ~ m( ∆ ,

± 1

χ ∼ b →

1

t ~ production,

1

t ~

1

t ~

)

th

σ 1 ± Observed limit ( )

exp

σ 1 ± Expected limit (

• 1

ATLAS 8 TeV, 20.3 fb

ATLAS Preliminary

• 1

= 13 TeV, 36.1 fb s Limit at 95% CL

Results: Compressed b+chargino

32

SLIDE 33

LHCP2017, May17 2017, Keisuke Yoshihara (University of Pennsylvania)

[GeV]

φ

m 10

2

10

3

10 (g=1.0)

Th

σ /

• bs

σ 95% CL limit on

1 −

10 1 10

2

10

3

10 Preliminary ATLAS

• 1

= 36.1 fb

int

= 13 TeV, L s Scalar χ χ → φ , φ + t t = 1.0 GeV

χ

g = 1.0, m Observed 95% CL Expected 95% CL σ 1 ± Expected σ 2 ± Expected (g=1.0) σ Theory unc. on [GeV]

a

m 10

2

10

3

10 (g=1.0)

Th

σ /

• bs

σ 95% CL limit on

1 −

10 1 10

2

10

3

10 Preliminary ATLAS

• 1

= 36.1 fb

int

= 13 TeV, L s Pseudoscalar χ χ → +a, a t t = 1.0 GeV

χ

g = 1.0, m Observed 95% CL Expected 95% CL σ 1 ± Expected σ 2 ± Expected (g=1.0) σ Theory unc. on [GeV]

χ

m 1 10

2

10 (g=1.0)

Th

σ /

• bs

σ 95% CL limit on

1 −

10 1 10

2

10

3

10

4

10

5

10

6

10 Preliminary ATLAS

• 1

= 36.1 fb

int

= 13 TeV, L s Scalar χ χ → φ , φ + t t = 10.0 GeV

φ

g = 1.0, m Observed 95% CL Expected 95% CL σ 1 ± Expected σ 2 ± Expected (g=1.0) σ Theory unc. on [GeV]

χ

m 1 10

2

10 (g=1.0)

Th

σ /

• bs

σ 95% CL limit on

1 −

10 1 10

2

10

3

10

4

10

5

10

6

10 Preliminary ATLAS

• 1

= 36.1 fb

int

= 13 TeV, L s Pseudoscalar χ χ → +a, a t t = 10.0 GeV

a

g = 1.0, m Observed 95% CL Expected 95% CL σ 1 ± Expected σ 2 ± Expected (g=1.0) σ Theory unc. on

Results: Spin-0 mediator model

33