Searches for 3rd generation SUSY-partners

Searches for 3rd generation SUSY-partners

”Particle Physics at the LHC”Simeon Schrott

08/07/2014

Simeon Schrott () Searches for 3rd generation SUSY-partners 08/07/2014 1 / 44

Outline

1 MotivationConsidered processes

2 Final states with zero leptonsSignal regionsBackground estimationResults

3 Final states with one leptonSignal regionsBackground estimationResults

4 State of the artCMS


Section 1

Motivation


Motivation

In several models, the partners of the top and the bottom quarks, thestops and the sbottoms, are predicted to be the lightest squarks for severalreasons:

diagonalizing the mass matrices in the basis of chiral eigenstates{t̃L, t̃R}/{b̃L, b̃R} leads to 2 mass eigenstates t̃1 and t̃2

M2t̃ =

m2t + m2

t̃L,b̃L+(

12− 2

3s2W

)M2

Z c2β mt (At − µ cot β)

mt (At − µ cot β) m2t + m2

t̃R+ 2

3s2WM2

Z c2β

(1)

M2b̃=

m2b + m2

t̃L,b̃L−(

12− 1

3s2W

)M2

Z c2β mb (Ab − µ tan β)

mb (Ab − µ tan β) m2b + m2

b̃R+ 1

3s2WM2

Z c2β

(2)

c2β ≡ cos 2β & s2W ≡ sin2 θW

by demanding a natural solution of hierarchy problem(natural SUSY models)

Trying to find squarks since using a pp-collider


Cross sections for SUSY production processes

Cross-sections for SUSY production processes


Considered processes

We only consider stop pair production

We assume there are only two simplified t̃1 decay modes:

- t̃1 → t χ̃01

- t̃1 → b χ̃±1 → b χ̃0

1 W (∗)

Assuming different BR for our analysis


Final states

Combining two final states of the t̃1 decay to get the final states ofdirect stop pair production

Final states of the t̃1 decay:

One lepton Zero lepton

Detector signature: 4+jets (2b-tagged) & large EmissT


Considered processes: Detector signature

EmissT = 896 GeV

5 jets

2 b-tagged jets(blue)

2 reclustered topcandidates


Section 2

Final states with zero leptons


Final states with zero leptons

Search for direct stop pair production

20.1 fb−1 of Atlas data used in this analysis

data was taken at√s = 8 TeV with the ATLAS detector at the LHC

Using all-hadronic final states only


Zero leptons: Signal regions

Defining 9 signal regions (SR)

SR main label criteria sensitive for:

SRA1-4 EmissT t̃1 → t χ̃0

1 & t̃1 → b χ̃±1

SRB1-2 Amt t̃1 → b χ̃±1

SRC1-3 mb,minT t̃1 → t χ̃0

1

with: Amt = top mass assymetry

mb,minT = transverse mass from Emiss

T and closest b-tagged jet


Zero leptons: Event selection requirement

SRA the fully resolved topology needs at least 6 jets.

Selection criteria for all SR Selection criteria for SRA


Zero leptons: mb,minT distribution

Eve

nts

/ 25

GeV

0

500

1000

Data 2012

SM Total

tt

Single Top

+Vtt

W

Z

Diboson

)=(600,1) GeV1

0χ∼,1t

~50 x (

)=(400,200,100) GeV1

0χ∼,

1

+χ∼,1t

~50 x (

ATLAS

=8 TeVs, -1L dt=20.1 fb∫Common selection

[GeV],minbTm

100 200 300 400 500

Dat

a / S

M

0.0

0.5

1.0

1.5

2.0

mb,minT distribution for events with at least 4 jets and all selection criteria

applied except mb,minT


Zero leptons: Event selection requirement

SRB and SRC are only partially resolved, SRB needing 4-5 jets and SRCexactly 5 jets.


Zero leptons: Background estimation

Example of final statewe want to detect

Main BG from tt̄production

BG from Z+jet (top)and W+jet (bottom)production


Zero leptons: Background estimation

All possible SM processes are background processes

BG simulated with Monte-Carlo (MC) simulations except forall-hadronic tt̄-production and multijet events, those were computedfrom data in control regions (CR) alone

CR used to adjust normalization to SR

Validation regions (VR) used to verify the normalization

CR and VR again chosen to be orthogonal to SR


Zero leptons: Selection criteria for the CR correspondingto SRA

Selection criteria for the CR of the SRA signal region

For the VR of SRA the same event selection criteria are applied except theτ -veto is inverted and requirements on the top mass and mb,min

T arechanged


Zero leptons: Normalized MC predictions and data inZ+jets CR

−1

)´ [5

0 G

eV]

mis

sT

E1/

N d

N/d

(

-310

-210

-110

1

10Data 2012

SM Total

Z

tt

Single Top

+Vtt

W

Diboson

ATLAS

=8 TeVs, -1L dt=20.3 fb∫4 jets≥Z+jets CR,

)´ [GeV]missTE(

0 200 400 600 800

Dat

a / S

M

0.0

0.5

1.0

1.5

2.0

EmissT -distribution in the Z+jets CR


Zero leptons: BG compared to data

Observed data and normalized BG in all CR


Zero leptons: Compare simulated and normalized BGto data in VR

Simulated and normalized BG in the VR


Zero leptons: EmissT distributions for SRA

[GeV]missTE

200 400 600 800

Eve

nts

/ 50

GeV

0

5

10

Data 2012SM TotalttSingle Top+Vtt

WZDiboson

)=(600,1) GeV1

0χ∼,1t~(

ATLAS

= 8 TeVs , -1L dt = 20.1 fb∫SRA1, SRA2

[GeV]missTE

400 600 800E

vent

s / 5

0 G

eV

0

2

4

6 Data 2012SM TotalttSingle Top+Vtt

WZDiboson

)=(600,1) GeV1

0χ∼,1t~(

ATLAS

= 8 TeVs , -1L dt = 20.1 fb∫SRA3, SRA4

EmissT -distributions for the signal regions SRA


Zero leptons: EmissT distributions for different SR

[GeV]missTE

400 600 800

Eve

nts

/ 50

GeV

0

2

4

6 Data 2012SM TotalttSingle Top+Vtt

WZDiboson

)=(600,1) GeV1

0χ∼,1t~(

ATLAS

= 8 TeVs , -1L dt = 20.1 fb∫SRB

[GeV]missTE

200 400 600 800

Eve

nts

/ 50

GeV

0

10

20

30

40Data 2012SM TotalttSingle Top+Vtt

WZDiboson

)=(400,200,100) GeV1

0χ∼,1

+χ∼,1t~(

ATLAS

= 8 TeVs , -1L dt = 20.1 fb∫SRC1

[GeV]missTE

200 400 600 800

Eve

nts

/ 50

GeV

0

10

20


WZDiboson

)=(400,200,100) GeV1

0χ∼,1

+χ∼,1t~(

ATLAS

= 8 TeVs , -1L dt = 20.1 fb∫SRC2

[GeV]missTE

200 400 600 800

Eve

nts

/ 50

GeV

0

5

10


WZDiboson

)=(400,200,100) GeV1

0χ∼,1

+χ∼,1t~(

ATLAS

= 8 TeVs , -1L dt = 20.1 fb∫SRC3

EmissT -distributions for the signal regions SRB & SRC


Zero leptons: Observed events in SR

Observed data in the SR


Zero leptons: Extracting cross sections

Simplified schematic illustration of obtaining the expected and the visiblecross section


Zero leptons: Results

No significant deviation from data tosimulated BG

Expected and observed cross-sectionsare equal within 2 σ

Applying models to redefine exclusionregions for the mass of the observed(?)sparticles

[GeV]1t

~m300 400 500 600 700

[pb]

σ

-310

-210

-110

1

10

210

310 = 50 GeV

1

0χ∼, m

1

0χ∼ t →1t~

production, 1t~

1t~

ATLAS Preliminary

All limits at 95% CL

T

miss1-lepton + jets + E

pair prod. cross section1t~

expected limit (mostly stop-right)

observed limit (mostly stop-right)

expected limit (purely stop-left)

observed limit (purely stop-left)

=8 TeVs, -1

L dt = 20.7 fb∫

(Only for illustration purpose)


Zero leptons: Exclusion contoures

200 300 400 500 600 700 8000

50

100

150

200

250

300

350

400

450

500

1

0χ∼+m

t<m

1t~m

)=100%0

1χ∼ t→ 1t

~(B production, 1t

~1t

~

[GeV]1

t~m

[GeV

]0 1χ∼

m

ATLAS

= 8 TeVs, -1

Ldt = 20.1 fb∫All-hadronic

All limits at 95 % CL

)theorySUSYσ1 ±Observed limit (

)expσ1 ±Expected limit (

= 7 TeV)sObserved limit (2011,

Assumptions: t̃1t̃1 production, B(t̃1 → t χ̃0

1

)= 100%


Zero leptons: Exclusion contoures

200 300 400 500 600 700 8000

50

100

150

200

250

300

350

400

450

500

)1

0χ∼ m×

= 2

1

±χ∼ (m

1

±χ∼+m

b < m1t~m

) = 50%0

1χ∼ t→ 1t

~(B),

1

0χ∼

m× = 2 1

±χ∼ (m±

1χ∼ b→ 1t

~ or

0

1χ∼ t→ 1t

~ production, 1t

~1t~

10χ∼+m

t<m

1t~m

<103.5 GeV1

±χ∼m

[GeV]1

t~m

[GeV

]0 1χ∼

m

ATLAS

= 8 TeVs, -1

Ldt = 20.1 fb∫All-hadronic

All limits at 95 % CL

)theorySUSYσ1 ±Observed limit (

)expσ1 ±Expected limit (


1

)= 50%


Section 3

Final states with one lepton


Final states with one lepton

Search for direct stop pair production

20.7 fb−1 of data used in this analysis

Data was taken with√s = 8 TeV with the ATLAS detector at the

LHC

Only using events with exactly one isolated lepton


One lepton: Signal regions

Defining 6 signal regions (SR), labeled SRbC for t̃1 → b χ̃±1

and SRtN for t̃1 → t χ̃01 decay modes.

SR sensitive for:

SRbC1 mχ̃±1

= 100− 300 GeV & mt̃1 = 200− 400 GeV

SRbC2 mt̃1 = 310− 500 GeV

SRbC3(mt̃1 −mχ̃±

1

)& 150 GeV

SRtN1 mt̃1 & mt + mχ̃01

SRtN2 large mχ̃01

SRtN3 large mt̃1


One lepton: Event selection requirements

Selection criteria defining the six SR


One lepton: Background estimation

Final states we want todetect

Main BG from tt̄production

BG from Z+jet (top)and W+jet (bottom)production


One lepton: Background estimation

Again all possible SM processes are background

Background simulated with MC Simulations

Using CR to normalize background to SR

Using VR to check normalization for tt̄-BG

CR and VR defined non overlapping with SR


One lepton: Characteristic distributions for different SRtNE

vent

s / 5

0 G

eV

-110

1

10

210

310

410

510

610

710

810Data 2012

Standard Model (SM)

tt

V+Jets, VV

+V, single top, multijetstt

= 25 [GeV]0χ = 225, mt~m

= 150 [GeV]0χ = 350, mt~m

-1 L dt = 20.7 fb∫ = 8 TeV, s

channelµe+

PreliminaryATLAS

SRtN1 shape

[GeV]TM0 50 100 150 200 250 300 350 400 450 500

Dat

a/S

M

0

1

2

Eve

nts

/ 50

GeV

-110

1

10

210

310

410

510Data 2012

Standard Model (SM)

tt

V+Jets, VV

+V, single top, multijetstt

= 200 [GeV]0χ = 500, mt~m

= 50 [GeV]0χ = 600, mt~m

-1 L dt = 20.7 fb∫ = 8 TeV, s

channelµe+

PreliminaryATLAS

SRtN2

[GeV]TmissE

200 250 300 350 400 450 500 550 600 650

Dat

a/S

M

0

1

2


One lepton: Observed events in SRbC

Table of events measured in the CR,VR and SR (for SRbC)Simeon Schrott () Searches for 3rd generation SUSY-partners 08/07/2014 35 / 44

One lepton: Observed events in SRtN

Table of events measured in the CR,VR and SR (for SRtN2-3)


One lepton: Observed events in SRtN1 shape

Table of events measured in the CR,VR and SR (for SRtN1)Simeon Schrott () Searches for 3rd generation SUSY-partners 08/07/2014 37 / 44

One lepton: Results

No significant deviation of simulated BG to data⇒ No evidence to physics beyond SM

Calculating expected and observed visible cross-sections

Applying certain models, one can calculate exclusion limits for theconsidered sparticle masses


One lepton: Excluded regions

[GeV]1

t~m

200 300 400 500 600 700 800

[G

eV

]10

��

m

0

50

100

150

200

250

300

350

400

t

< m

1

0

��

- m

1t~

m

1

0�� t �1t

~ production, 1t

~1t

~

)exp1 !Expected limit (

Expected limit (HCP12)

)theory

SUSY1 !Observed limit (ATLAS Preliminary

All limits at 95% CLT


=8 TeVs, -1

L dt = 20.7 fb


1

)= 100%


One lepton: Excluded regions

[GeV]1t

~m

200 250 300 350 400 450 500 550 600

[G

eV

]10

m

0

50

100

150

200

250 = 150 GeV!

1��

, m1

0+

(*) W

1

!,

1

! b+ 1t

~ production, 1t

~1t

~

)exp1 !Expected limit (


)theory

SUSY1 !Observed limit (

ATLAS Preliminary

All limits at 95% CLT


=8 TeVs, -1

L dt = 20.7 fb

( = 150 GeV) !

1�� > m

1

0�� m

[GeV]1

t~m

100 200 300 400 500 600 700

[G

eV

]10

m60

80

100

120

140

160

180

200

220

240

2601

0��m! = 2"

1��

, m1

0+

(*) W

1

",

1

" b+

1t~

production, 1t~1t~

ATLAS Preliminary

T


=8 TeVs, -1

L dt = 20.7 fb

)1

0

��

m!

= 2

1

"

��

( m

1

"

��

+m

b

< m

1t~m

)exp1 "Expected limit (


)theory

SUSY1 "Observed limit (

1-2 leptons (2011)


Assumptions: t̃1t̃1 production, B(t̃1 → b χ̃±

1

)= 100%,

left: mχ̃±1

= 150 GeV, right: mχ̃±1

= 2 ·mχ̃01


Section 4

State of the art


State of the art of the ATLAS Experiment

[GeV]1t

~m

100 200 300 400 500 600 700

10

χ∼+mt

< m

1t~m

10

χ∼

+ m

W

+ m

b

< m

1t~m

10

χ∼

+ m

c

< m

1t~m

200 300 400 500 600

)1

0χ∼ m×

= 2

1

±χ∼ ( m

1

±χ∼+m

b < m1t~m

< 106 GeV 1

±χ∼ m

( = 150 GeV)1

±χ∼ > m1

0χ∼

m

+5 G

eV)

10χ∼

= m

1±χ∼

( m

1±χ∼

+mb

< m

1t~m

< 103.5 GeV1

±χ∼m

[GeV

]10 χ∼

m

0

100

200

300

400

500

600

Observed limits

Expected limits


[1203.4171]-1CDF 2.6 fb

ATLAS Preliminary

production1t~1t

~Status: Moriond 2014

=8 TeVs -1 = 20 - 21 fbintL =7 TeVs -1 = 4.7 fbintL

0L ATLAS-CONF-2013-024

1L ATLAS-CONF-2013-037

2L [1403.4853]

2L [1403.4853]

0L mono-jet/c-tag, CONF-2013-068

0L [1308.2631]

2L [1403.4853]

1L CONF-2013-037, 0L [1308.2631]

2L [1403.4853]

1L CONF-2013-037, 2L [1403.4853]

0L [1208.1447]

1L [1208.2590]

2L [1209.4186]

-

-

-

2L [1208.4305], 1-2L [1209.2102]

-

-

1-2L [1209.2102]

1

0χ∼ (*) W→

1

±χ∼, 1

±χ∼ b → 1t~

1

0χ∼ t →1t~

/ 1

0χ∼ W b →1t~

/ 1

0χ∼ c →1t~

0L,

1L,

2L,

2L,0L,

0L,

1-2L,

1L,

2L,1-2L,

1

0χ∼ t →1t~

1

0χ∼ t →1t~

1

0χ∼ t →1t~

1

0χ∼ W b →1t~

1

0χ∼ c →1t~ mono-jet/c-tag,

+ 5 GeV1

0χ∼ = m±

1χ m

= 106 GeV±1

χ, m

1

±χ∼ b → 1t~

= 150 GeV±1

χ, m

1

±χ∼ b → 1t~

- 10 GeV1t~ = m±

1χ

, m1

±χ∼ b → 1t~

1

0χ∼ m× = 2 ±1

χ, m

1

±χ∼ b → 1t~


Comparing Achievements with results from CMS

stop mass [GeV]

100 200 300 400 500 600 700 800

LSP

mas

s [G

eV]

0

50

100

150

200

250

300

350

400

450

500

W

=m1

0χ∼

-mt~

m

t

=m1

0χ∼

-mt~

m

SUSY 2013 = 8 TeVs

CMS Preliminary

productiont~-t

~

)1

0χ∼ t →t~ (-1SUS-13-004 0-lep+1-lep (Razor) 19.3 fb

)1

0χ∼ t →t~ (-1SUS-13-011 1-lep (leptonic stop)19.5 fb

, x=0.25)1

+χ∼ b →t~ (-1SUS-13-011 1-lep (leptonic stop)19.5 fb

Observed

Expected

W

=m1

0χ∼

-m1

±χ∼m

Exclusion limits observed by CMS are similar to those measured by ATLAS


Summarization

Observed events agree with SM predictions

No evidence for physics beyond the SM

Mass exclusion regions could be extended


Searches for 3rd generation SUSY-partners

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