bsm searches at atlas€¦ · the atlas susy, exotics and higgs groups search for a wide range of...

BSM searches at ATLAS

Run-1 Anomalies, Bumps and Deviations

Alex Martyniuk, UCL

November 5, 2015

1 / 35 Alex Martyniuk BSM searches at ATLAS

Introduction – Standard Model @ ATLAS

pp

total

80 µb−1

JetsR=0.4

|y |<3.0

0.1< pT < 2 TeV

DijetsR=0.4

|y |<3.0y ∗<3.0

0.3<mjj < 5 TeV

W

fiducial

35 pb−1nj ≥ 0

nj ≥ 1

nj ≥ 2

nj ≥ 3

nj ≥ 4

nj ≥ 5

nj ≥ 6

nj ≥ 7

Z

fiducial

35 pb−1nj ≥ 0

nj ≥ 1

nj ≥ 2

nj ≥ 3

nj ≥ 4

nj ≥ 5

nj ≥ 6

nj ≥ 7

t̄t

fiducial

e, µ+X

nj ≥ 4

nj ≥ 5

nj ≥ 6

nj ≥ 7

nj ≥ 8

tt−chan

total

WW

total

γγ

fiducial

Wt

total

2.0 fb−1

H

fiducial

H→γγ

VBFH→WW

ggFH→WW

H→ZZ→4ℓ

total(γγ,ZZ )

H→ττ

WZ

total

13.0 fb−1

ZZ

total

Wγ

fiducial

WW+WZ

semilept.fiducial

Zγ

fiducial

t̄tW

total

t̄tZ

total

95% CL

upper

limit

t̄tγ

fiducial

ZjjEWK

fiducial

Wγγ

fiducialnjet=0

W±W±jjEWK

fiducial

ts−chan

total

95% CL

upper

limit

0.7 fb−1

σ[p

b]

10−3

10−2

10−1

1

101

102

103

104

105

106

1011

LHC pp√s = 7 TeV

Theory

Observed 4.5 − 4.9 fb−1

LHC pp√s = 8 TeV

Theory

Observed 20.3 fb−1

Standard Model Production Cross Section Measurements Status: March 2015

ATLAS Preliminary

Run 1√s = 7, 8 TeV


Introduction – The Problems

Things are not as rosy as they seem for the Standard Model (SM)

Problems lurk within.....It contains no dark matter candidateIt requires immense fine tuning for the 125 GeV Higgs to make senseIt does not contain gravity

Beyond the SM (BSM) theories try to solve these issues

The ATLAS SUSY, Exotics and Higgs groups search for a wide range of BSMphysics utilising the full ATLAS detector

Often at the limits or beyond the specification the detector

We built a general purpose detector for a reason!


Introduction – Obligatory ATLAS Slide


Outline – What I will show

I will cover a whirlwind tour of three searches from the ATLAS Exotics/SUSYgroups that had some ‘oddities’ in Run-1

SUSY: Pair produced cascade decays search using same-flavouropposite-sign dilepton pair, jets, and large missing transverse momentum

[SUSY-2014-10]

Exotics: Search for anomalous production of b-jets and a pair of leptons of thesame charge

[EXOT-2013-16]

Exotics: Search for diboson resonances decaying to boson-tagged jets[EXOT-2013-08]*Fair warning, I worked directly on this analysis and might well be biased to spend more time here...


https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/SUSY-2014-10/

https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/EXOT-2013-16/


SUSY Searches – needle in the haystack?


SUSY Searches – ExclusionsATLAS SUSY summary papers out now,[SUSY-2014-05], [SUSY-2014-06], [SUSY-2014-07], [SUSY-2014-08]

[GeV]1t

~m

200 300 400 500 600 700 800

[G

eV

]10

χ∼m

0

50

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1

0χ∼ t →

1t~

1

0χ∼ t →

1t~

1

0χ∼/b f f’

1

0χ∼ W b →

1t~

1

0χ∼ W b →

1t~

1

0χ∼ c →

1t~

1

0χ∼ b f f’ →

1t~

1

0χ∼

,t) <

m1t~

m(

∆

W

+ m

b

) <

m1

0χ∼,

1t~ m

(∆

) <

01

0χ∼,

1t~ m

(∆

1

0χ∼ t →1t

~ /

1

0χ∼ W b →1t

~ /

1

0χ∼ c →1t

~ /

1

0χ∼ b f f’ →1t

~ production, 1t

~1t

~

ATLAS

1

0χ∼W b

1

0χ∼c

1

0χ∼b f f’

Observed limits Expected limits All limits at 95% CL

1=8 TeV, 20 fbs

t0L/t1L combined

t2L, SC

WW

t1L, t2L

tc

tc, t1L [GeV]

1t~m

170 180 190 200 210

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eV

]10

χ∼m

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χ∼m

(

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1000

, x=1/20

1χ∼0

1χ∼ qqWW→ q

~q

~

ATLAS

1=8 TeV, 20 fbs

0L + 1L combination

)1

0

χ∼

) < m

(

q~m(

)theory

SUSYσ1 ±Observed limit (

)expσ1 ±Expected limit (

1lepton alone

0lepton alone

All limits at 95% CL

[GeV]±

1χ∼m

100 200 300 400 500 600 700 800

[G

eV

]0 1

χ∼m

0

100

200

300

400

500

600

0

1χ∼

= m

±

1χ∼m

1=8 TeV, 20.3 fbs


lCombined SS MVA, 3

0

1χ∼

) ν ν l l (0

1χ∼ ν l →) ν ν

∼l (Ll

~ ν

∼), l ν ν

∼l(

Ll~ ν

Ll~ →

0

2χ∼

±

1χ∼

Simplified Model:

)0

1χ∼ m

±

1χ∼ + 0.95*(m0

1χ∼ = m

Ll~

m

0

2χ∼ = m±

1χ∼m

ATLAS

)theory



lObserved limit 3

Observed limit SS MVA

) [GeV]g~

m(

400 600 800 1000 1200 1400

) [G

eV

]10

χ∼m

(

100

200

300

400

500

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1000

, x=1/20

1χ∼0

1χ∼ qqqqWW→ g

~g

~

ATLAS

1=8 TeV, 20 fbs

0L + 1L combination)1

0

χ∼

) < m

(

g~m

(

)theory



1lepton alone

0lepton alone


Fra

ctio

n of

Mod

els

Exc

lude

d

0

0.2

0.4

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0.8

1

) [GeV]g~m(

0 500 1000 1500 2000

) [G

eV]

0 1χ∼m

(

0

500

1000

LSP0

1χ∼pMSSM:

1−=8 TeV, 20.3 fbs

[1405.7875]0

1χ∼ qq→ g~

ATLAS

Fra

ctio

n of

Mod

els

Exc

lude

d

0

0.2

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0.8

1

) [GeV]g~m(

0 500 1000 1500 2000)

[GeV

]q~

m(

0

1000

2000

3000

LSP0

1χ∼pMSSM:

1−=8 TeV, 20.3 fbs

)=0 GeV [1405.7875]0

1χ∼m(

ATLAS






SUSY search using ll + jets + EmissT

[SUSY-2014-10]

‘Standard’ ATLAS SUSY search methodologyControl regions (CRs): Used to constrain SM backgroundsValidation regions (VRs): CR background estimates extrapolated into VRs ascross-checkSignal regions (SRs): After VR check, extrapolate background into SR and look forexcess of events over expected backgroundSearch performed over a grid of signal masses



On shell Z channel regions

Backgrounds studiedFlavour symmetric t t̄ , WW , Wt : Data-driven.CReµ data (corrected for other backgrounds).Lepton selection eff. relations transfer to SR.Cross-checked with Z -mass sidebands. MCnorm. in CRT, extrapolation checked in VRT/Z.Z/γ+ jets: Data-driven. Seed CR jets smearedto mimic Emiss

T distribution. Tested in VRZ region.Fake leptons: Data-driven. Derived from matrixmethod.Other backgrounds. WZ , ZZ , Rare top. Modelledby MC.


Flavour symmetric modellingBackground normalisation modelling in goodagreement with the data in the flavour symmetriccross-check CR/VRs (Z/γ+ jets in backup)

High-HT : HT > 600 GeV

High-EmissT : Emiss

T > 225 GeV, 400 > HT > 600 GeV

VRT

(HT > 500 GeV)

��

��

��

CRT

(HT > 600 GeV)

SR-Z

(HT > 600 GeV)

VRT

(HT > 500 GeV)

VRTZ

(HT > 500 GeV)

CRT

(HT > 600 GeV)

� ��

��

Eve

nts

1

10

210

310

Data

Flavour Symmetric

* + jetsγZ/

Other Backgrounds

Total SM

-1=8 TeV, 20.3 fbsATLAS

Z-mass side band Z-mass window

CRT VRT VRT VRT VRTZ VRTZ VRTZ

tot

σ)

/ ex

p -

Nob

s(N -2

0

2

4 µµee+ee

µµ

)T

(high H )miss

T(high E )

T(high H )

miss

T(high E


SR Results

Excesses seen in both channels (ee: 3.0σ, µµ: 1.7σ)

Combined significance 3.0σ

CMS observes no excess

[GeV]llm82 84 86 88 90 92 94 96 98 100

Eve

nts

/ 2.5

GeV

2

4

6

8

10

12

14ATLAS

-1 = 8 TeV, 20.3 fbs

SR-Z ee

DataStandard ModelFlavour SymmetricOther Backgrounds

=(700,200)GeVµ),g~m(=(900,600)GeVµ),g~m(

[GeV]missTE

200 250 300 350 400 450 500

Eve

nts

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GeV

2

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12ATLAS

-1 = 8 TeV, 20.3 fbs

SR-Z ee


=(700,200)GeVµ),g~m(=(900,600)GeVµ),g~m(

[GeV]llm82 84 86 88 90 92 94 96 98 100

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nts

/ 2.5

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µµSR-Z


=(700,200)GeVµ),g~m(=(900,600)GeVµ),g~m(

[GeV]missTE

200 250 300 350 400 450 500

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nts

/ 25

GeV

2

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12ATLAS

-1 = 8 TeV, 20.3 fbs

µµSR-Z


=(700,200)GeVµ),g~m(=(900,600)GeVµ),g~m(


Summary – ll + jets + EmissT

Channel searches for SUSY cascade decays with SF leptons, jets and EmissT both

on and off Z mass shellCombined significance 3.0σExcesses seen in both on shell channels, therefore weaker limitsDevil’s advocate/pessimist in me:

≈ 180 SR in SUSY searches Run-1Would naively expect ≈ 0.5× 3σ excesses and have seen oneOnly Run-2 will tell

[GeV]llm82 84 86 88 90 92 94 96 98 100

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nts

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-1 = 8 TeV, 20.3 fbs

SR-Z ee


=(700,200)GeVµ),g~m(=(900,600)GeVµ),g~m(

[GeV]µ200 400 600 800 1000

) [G

eV]

g~m

(

600

700

800

900

1000

1100

1200

1300

1400

)0

1χ∼

) < m

(

g~m(

200 300 400 500 600 700 ) [GeV]0

1χ∼m(

)=1.5 TeVq~ = 1 TeV, m(2 = M1

= 1.5, Mβ; tan0

1χ∼GGM: higgsino-like

-1=8 TeV, 20.3 fbs

µµSR-Z ee+

ATLAS )theorySUSYσ1 ±Observed limit (




Exotic Searches – LLP

Model Signature∫L dt[fb−1] Lifetime limit Reference

SU

SY

Hig

gsB

R=

10%

Hig

gsB

R=

5%30

0G

eVsc

alar

900

GeV

scal

arO

ther

RPV χ01 → eeν/eµν/µµν displaced lepton pair 20.3 1504.05162m(g̃) = 1.3 TeV, m(χ01) = 1.0 TeV7-740 mmχ01

lifetime

GGM χ01 → ZG̃ displaced vtx + jets 20.3 1504.05162m(g̃) = 1.1 TeV, m(χ01) = 1.0 TeV6-480 mmχ01

lifetime

AMSB pp → χ±1χ01,χ+1 χ−1 disappearing track 20.3 1310.3675m(χ±1 ) = 450 GeV0.22-3.0 mχ±1

lifetime

AMSB pp → χ±1χ01,χ+1 χ−1 large pixel dE/dx 18.4 1506.05332m(χ±1 ) = 450 GeV1.31-9.0 mχ±1

lifetime

GMSB non-pointing or delayed γ 20.3 1409.5542SPS8 with Λ = 200 TeV0.08-5.4 mχ01

lifetime

Stealth SUSY 2 ID/MS vertices 19.5 1504.03634m(g̃) = 500 GeV0.12-90.6 mS̃ lifetime

Hidden Valley H → πvπv 2 low-EMF trackless jets 20.3 1501.04020m(πv) = 25 GeV0.41-7.57 mπv lifetime

Hidden Valley H → πvπv 2 ID/MS vertices 19.5 1504.03634m(πv) = 25 GeV0.31-25.4 mπv lifetime

FRVZ H → 2γd + X 2 e−, µ−,π−jets 20.3 1409.0746H → 2γd + X , m(γd ) = 400 MeV14-140 mmγd lifetime


Hidden Valley H → πvπv 2 low-EMF trackless jets 20.3 1501.04020m(πv) = 25 GeV0.6-5.0 mπv lifetime

Hidden Valley H → πvπv 2 ID/MS vertices 19.5 1504.03634m(πv) = 25 GeV0.43-18.1 mπv lifetime


Hidden Valley Φ→ πvπv 2 low-EMF trackless jets 20.3 1501.04020σ×BR = 1 pb, m(πv) = 50 GeV0.29-7.9 mπv lifetime

Hidden Valley Φ→ πvπv 2 ID/MS vertices 19.5 1504.03634σ×BR = 1 pb, m(πv) = 50 GeV0.19-31.9 mπv lifetime

Hidden Valley Φ→ πvπv 2 low-EMF trackless jets 20.3 1501.04020σ×BR = 1 pb, m(πv) = 50 GeV0.15-4.1 mπv lifetime

Hidden Valley Φ→ πvπv 2 ID/MS vertices 19.5 1504.03634σ×BR = 1 pb, m(πv) = 50 GeV0.11-18.3 mπv lifetime

HV Z ′(1 TeV)→ qvqv 2 ID/MS vertices 20.3 1504.03634σ×BR = 1 pb, m(πv) = 50 GeV0.1-4.9 mπv lifetime

HV Z ′(2 TeV)→ qvqv 2 ID/MS vertices 20.3 1504.03634σ×BR = 1 pb, m(πv) = 50 GeV0.1-10.1 mπv lifetime

cτ [m]0.01 0.1 1 10 100√s = 8 TeV

ATLAS Long-lived Particle Searches* - 95% CL ExclusionStatus: July 2015

ATLAS Preliminary∫L dt = (18.4 - 20.3) fb−1

√s = 8 TeV

*Only a selection of the available lifetime limits on new states is shown.


Exotic Searches – needles in the haystack?


Exotics search in ll + b − jets + EmissT

[EXOT-2013-16]g

T̄

Z

g

g

T

H

t

t̄

g

σ

t

t̄

t

g

g

σ

t̄

u, c

u, c t

H

t

Look for excess of events with same-sign (SS) lepton pairs, b-jets and EmissT

Using a simple ‘cut and count’ methodology

As most Exotics analyses do, the channel is sensitive to a wide range of BSMtheories

Vector-like quarks (VLQ)Any enhancement of t t̄ t t̄ production (g̃ pair production, 2UED/RPP)Chiral quark production, b′ → WtSame-sign tt production via flavour changing neutral currents (FCNC)



Signal regionsg

σ

t

t̄

t

g

g

σ

t̄

Backgrounds studiedReal SS lepton pairs W ±W ± jj , t t̄W/Z ,t t̄W +W−, t t̄H, WH, ZH, tWZ , tH, WZ , ZZ andt t̄ t t̄ : MC modelled (low x-sections)Fake leptons: Data-driven. Derived from matrixmethod.Charge misidentification: Rate estimated inZ → ee events

Estimates validated in low-HT region,100 > HT > 400 GeV

Definition Namee±e± + e±µ± + µ±µ± + eee+ eeµ+ eµµ+ µµµ, Nj ≥ 2

400 < HT < 700GeVNb = 1 SRVLQ0Nb = 2 Emiss

T > 40 GeV SRVLQ1 SR4t0Nb ≥ 3 SRVLQ2 SR4t1

HT ≥ 700 GeV

Nb = 140 < Emiss

T < 100GeV SRVLQ3Emiss

T ≥ 100 GeV SRVLQ4

Nb = 240 < Emiss

T < 100GeV SRVLQ5 SR4t2Emiss

T ≥ 100 GeV SRVLQ6 SR4t3Nb ≥ 3 Emiss

T > 40 GeV SRVLQ7 SR4t4e+e+, e+µ+, µ+µ+, Nj ∈ [2, 4], ∆φ`` > 2.5

HT > 450 GeV Nb ≥ 1 EmissT > 40 GeV SRttee, SRtteµ, SRttµµ


Preselection Results

Preselection appliedEssentiallySRLQ0/1/2 withoutthe HT or Emiss

Tselections applied

Good data/backgroundagreement withinuncertainties seen inpreselection withone/two b-tagged jets

Good agreement alsoseen in the validationregions

[GeV]missTE

0 50 100 150 200 250 300 E

vent

s / 1

0 G

eV0

20

40

60

80

100

120

140

160

180

200 Data

W/Ztt

Q Mis-id

Non-prompt/fakes

Htt

Dibosons

Other

Uncertainties

ATLAS-1 = 8 TeV, 20.3 fbs

preselection + 1 b-jet

[GeV]missTE

0 50 100 150 200 250 300

Eve

nts

/ 10

GeV

0

10

20

30

40

50

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Data

W/Ztt

Q Mis-id

Non-prompt/fakes

Htt

Dibosons

Other

Uncertainties


preselection + 2 b-jets

[GeV]TH0 200 400 600 800 1000 1200 1400 1600

Eve

nts

/ 50

GeV

0

50

100

150

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250

300

Data

W/Ztt

Q Mis-id

Non-prompt/fakes

Htt

Dibosons

Other

Uncertainties


preselection + 1 b-jet

[GeV]TH0 200 400 600 800 1000 1200 1400 1600

Eve

nts

/ 50

GeV

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90Data

W/Ztt

Q Mis-id

Non-prompt/fakes

Htt

Dibosons

Other

Uncertainties


preselection + 2 b-jets


SR Results

Excess of 2.0σ seen taking all SRVLQs into account (VLQ and b′ models)Excess of 2.5σ seen taking only 4-top SRs into accountSS+FCNC SRs are in good agreement with SM expectation

Eve

nts

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W/ZttQ Mis-idFake/non-prompt leptons

HttDibosonsOtherUncertainties


SRVLQ0 SR4t0SRVLQ1

SR4t1SRVLQ2 SRVLQ3 SRVLQ4

SR4t2SRVLQ5

SR4t3SRVLQ6

SR4t4SRVLQ7

Sig

nific

ance

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SRVLQ0 SR4t0SRVLQ1


SR4t2SRVLQ5

SR4t3SRVLQ6

SR4t4SRVLQ7

Sig

nific

ance

-3-2-10123


Summary – ll + b − jets + EmissT

Cut/count analysis looking for events with SS lepton pairs and b-jets as a signalfor many BSM signalsExcesses of 2.5σ(2.0σ) seen taking 4-top SRs(all SRs) into accountMass resolution of the analysis is poorLimits worse than expected due to presence of excessAgain Run-2 is needed to to elucidate the origin of this excess

Signal mass [TeV]

0.4 0.6 0.8 1 1.2

p-va

lue

-310

-210

-110

1

σ1

σ2

σ3



SgluonUED-RPP

Sgluon mass [TeV]

0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2

) [p

b]ttt

BR

(t× σ

-310

-210

-110

1

10


95% CL observed limit

95% CL expected limit

95% CL expected limitσ 1±

95% CL expected limitσ 2±

) = 100%]t t→ σTheory [BR(


Exotics search in X → VV → JJ

[EXOT-2013-08] Bias starts here

Diboson resonances appear in manyextensions to the standard model

The following analysis concentrates ontwo benchmark models

Extended gauge sector models(W ′ → WZ )Extra dimensions models(GRS → WW/ZZ )

Low branching ratios hinder theleptonic searches at the highest masses

Obviously, a fully hadronic search hasaccess to these lost events

The problem, is controlling theenormous QCD background that theleptonic searches were avoiding

W ⇓ Diboson branching ratioslν (33%) 23% 7% 3%qq (67%) 47% 13% 7%

Z ⇒ qq (70%) νν (20%) ll (10%)

Use large-R jets and jet substructureto select signal events from dominantQCD multi-jet backgrounds



Boosted Bosons

WI WZ Large ΔR

Large ΔR

Low Mass <500GeV

WI WZ

High Mass >1TeV

Small ΔR

Small ΔR

Increasing Mass

Vector bosons have massO(0.1 TeV)

We are interested in particlesof mass ≥ O(1 TeV)

Therefore the decays of theform, X → VV with large mX ,lead to vector bosons withvery high pT

Therefore, boosted decayproducts become morecollimatedRule of thumb for angularseparation of decay products:

∆R =√

∆φ2 + ∆η2 ≈ 2mpT


Fat Jet→Grooming→Tagging1 Reconstruct decay as fat-jet

Use large-R parameter jet to collect radiation from the original decay2 Groom the jet

Signal: Remove unwanted jet constituents not from the signal, e.g. pile-upBackground: Preserve the background characteristics

3 Tag as boson jetUse differences between signal and background jet characteristics to rejectbackground jets


BDRS-A Split-Filter

In this analysis a modified BDRS-Asplit filtering algorithm is used

Starts from R = 1.2 CA jets seededfrom local cluster weighted (LCW)topological clusters

Loose BDRS tagger, with no massdrop requirement

Iterative parameter Value√ymin 0.20µmax 1.00

Filtering parameter Valuenr 3Rr 0.3


Event selection1 Trigger: pT > 360 GeV anti-kt 1.02 Apply BDRS-A split-filter3 Require mJJ > 1.05 TeV

Ensures on trigger plateau

4 Rapidity gap between leading jets,|∆y12| < 1.2

s-channel signal more central thant-channel QCD

5 Leading jets pT asymmetry ApT < 0.15Used as proxy for large-R jet cleaning

6 Leading jets |η| < 2.0Ensures a good overlap with tracker

7 Correction for jets on calorimetry holes8 Boson tagging cuts

Jet mass (WZ , WW , ZZ ), momentumbalance, ntrk ghost associated to jet

Background efficienciesTopological ε ≈ 48%Tagger ε ≈ 1.2− 0.6% (per jet)

1.5 2 2.5 3 3.5

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Data

Background model

Significance (stat)

Significance (stat + syst)


No boson tagging

[TeV]jjm1.5 2 2.5 3 3.5

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ance

2−024











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)T2

+pT1

)/(pT2

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< 1.54 TeVjj m≤1.26

)T2

+pT1

)/(pT2

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Resonance Mass [TeV]1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3

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X →WZ selection

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WZ Selection

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Sig

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Full WZ selection appliedZ mass window appliedto leading mass jetW mass windowapplied to sub-leadingmass jet

Good agreement seen withsteeply, smoothly fallingbackground model in thelow/high mass regions

Deviation from thebackground observed ataround 2 TeV


X →WW selection

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WW Selection

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Sig

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Full WW selection applied tothe data

W mass windowapplied to both jets

Good agreement again seenwith steeply, smoothly fallingbackground model

Deviation from thebackground still observed ataround 2 TeV

Remember: There is anoverlap between the W /Zmass windows


X → ZZ selection

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Full ZZ selection applied tothe data

Z mass windowapplied to both jets

Good agreement again seenwith steeply, smoothly fallingbackground model

Deviation from thebackground still observed ataround 2 TeV

Remember: There is anoverlap between the W /Zmass windows


Observed p0 value

[GeV]jjm1400 1600 1800 2000 2200 2400 2600 2800 3000

0Lo

cal p

4−10

3−10

2−10

1−10

1

10WZ Selection

WW Selection

ZZ Selection

ATLAS-1=8TeV, 20.3 fbs

σ0

σ1

σ2

σ3

σ3.5

σ4

Therefore, no statistically significant deviation fromthe background has been observed

A discrepancy was seenwith respect to theexpected backgrounddistribution

Once suitably confident itis not an error, itssignificance should bequantifiedIn the WZ channel:

Local p0 = 3.4σ

Global p0 = 2.5σGlobal σ takes intoaccount the lookelsewhere effectLEE includes weightedcontribution fromWW /ZZ channels dueto the overlap


X →WZ limits

As no significant deviation was observed, we continue to set limits on theobserved distributions

95% confidence limits set on σ × B using the CLS prescription taking intoaccount the systematic uncertainties and background fit

[TeV]W' m1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3

WZ

) [fb

]→

BR

(W'

× W

') →

(pp

σ

1−10

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Expected 95% CL

uncertaintyσ 1±

unceirtaintyσ 2±

EGM W', c = 1


Expected limits broadlyagree with the observedlimits

Exclusion of EGM W ′

from 1.3− 1.5 TeV

Broad deviation from thebackground observable ataround 2 TeV

Benchmark extendedgauge model W ′ σ × Bshown for comparisonpurposes

WW , ZZ in backup


Are we alone? ATLAS combination

ATLAS diboson combination ATLAS-CONF-2015-045

In the full combination discrepancy is reduced to a 2.5σ local excess

Limits increased to 1.81TeV in the W ′ search channels

Fully hadronic channel in (significant) tension with the leptonic channelsPointing to statistical fluctuation in fully hadronic channel?Run-2 will sort this out!

Full paper following up CONF note in the ATLAS pipeline


https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2015-045/

Summary – X → VV → JJ

Presented a search for a high mass dibosonresonance, [arXiv:1506.00962]

Used 20.3fb−1 8TeV ATLAS dataJet substructure (BDRS-A CA 1.2 jets) used toseparate signal from backgroundQCD dominated background modelled byparametric function

Deviation from expected steeply, smoothly fallingbackground seen at 2 TeVCross-checks performed, no major issuesdiscovered

Excess p0 = 3.4σ local, 2.5σ global

Limits exclude EGM W ′ models with1.3 < mW ′ < 1.5 TeV

Combination with other diboson search channelsreduces excess to 2.5σ local

Preparations underway to repeat search in13TeV data

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[TeV]jjm1.5 2 2.5 3 3.5

Sig

nific

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2−1−0123

[TeV]W' m1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3

WZ

) [fb

]→

BR

(W'

× W

') →

(pp

σ

1−10

1

10

210

310

410 Observed 95% CL

Expected 95% CL

uncertaintyσ 1±

unceirtaintyσ 2±

EGM W', c = 1



http://arxiv.org/abs/1506.00962

The Future: Run-2


The Future How soon is now?


How much data is needed?

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So question one is how muchRun-2 13 TeV data do we needto surpass for example theRun-1 VV → JJ result?

At 2 TeV productioncross-sections growconsiderably

For gluon-gluon fusion ×15,i.e. for GRS productionFor qq̄ initiated ×8, i.e. forW′ productionUnfortunately QCDbackground also increases

So a smaller amount of Run-2data (1− 3fb−1) should beroughly equivalent to the 8 TeVdataset


How much data is needed?

100 10001

10

100

gg

Σqq

qg

WJS2013

ratios of LHC parton luminosities: 13 TeV / 8 TeV

lum

ino

sity r

atio

MX (GeV)

MSTW2008NLO

_

So question one is how muchRun-2 13 TeV data do we needto surpass for example theRun-1 VV → JJ result?

At 2 TeV productioncross-sections growconsiderably

For gluon-gluon fusion ×15,i.e. for GRS productionFor qq̄ initiated ×8, i.e. forW′ productionUnfortunately QCDbackground also increases

So a smaller amount of Run-2data (1− 3fb−1) should beroughly equivalent to the 8 TeVdataset


Conclusions

Presented a series of searches for BSM physics by the ATLAS SUSY andExotics groups in Run-1 of the LHC which showed anomalous features

All used 20.3fb−1 8TeV ATLAS data

Deviations between 2− 3.5σ local observed

In the VV → JJ search a global significance of 2.5σ was observed, beforecombination with the leptonic channels

[GeV]llm82 84 86 88 90 92 94 96 98 100

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Backup

Backup


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Cambridge-Aachen Jets

Cambridge-Aachen jets (CA jets)[arXiv:9707323] or [arXiv:0802.2470]

Part of the sequential recombinationfamily of jet reconstruction algorithms

Calculate the ∆Rij between all jetconstituentsCombine closest constituents firstMerge while R ≤ 1.2 (in this analysis)If there are no components within 1.2,redefine as a jet and remove from thecollection of constituentsMerge until there are no componentsleft

NO pT dependence!

Therefore can look into the history anduse the pT splitting information


http://arxiv.org/pdf/hep-ph/9707323v2.pdf


BDRS Split-FilterThe BDRS split filtering algorithm, [arXiv:0802.2470], decomposes CA jetssequential clustering to find hard substructure withinOriginally defined to find boosted H → bb decays

The decomposition follows some simple stepsFor jet j , undo the last step of clustering forming jets j1 and j2 (mj1 > mj2 )If there was a large mass drop, mj1 < µmaxmj and the pT balance is not too

asymmetric,min(p2

Tj1,p2

Tj2)

m2j0

∆R2j1,j2≥ ymin, define j as from a hard splitting and stop

Otherwise redefine j as j1, discard j2, and continueFilter the resulting jet by re-clustering as nr × Rr sized subjets



BDRS-A CA R = 1.2 Jet Calibration

Particle level jet energy and mass calibrations were derived and applied to theBDRS-A CA R = 1.2 jets used in the analysisEffectively restores jet energy/mass response over the full jet E and η range

Calculate the jet energyresponse in bins of ηdetand Etruth

Fit the responses with aGaussian fit, to gainmean response in eachbin, < Rjet

E >

Derive the meanreconstructed jet energy,< Ejet

reco >

Fit the < RjetE > vs

< Ejetreco > distribution to

gain a calibrationfunctionRepeat process formass calibration usingthe LCW+JES jets

ηJet -2 -1.5 -1 -0.5 0 0.5 1 1.5 2

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ATLAS Simulation

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Tagging selection applied

= 8 TeVsPythia 8 dijets,

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Tools: Jet mass

2 Filtered jet massSeparates peaked boson mass from falling QCD spectrum

Apply ±13 GeV window cutsaround boson mass from MCsimulation peak (mW = 82.4,mZ = 92.8)

For example, in the WZ cut;Leading mass jet79.8 GeV < mjet < 105.8 GeVSubleading mass jet69.4 GeV < mjet < 95.4 GeV

Very powerful cut!εsignal ≈ 80%εbackground ≈ 10− 15%

Cuts optimised using a data CRDijet formed from twotagged/un-tagged regions

N.B. Windows overlap!!!

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Pythia QCD dijet

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Tools: Subjet momentum balance

3 Subjet momentum balanceBoson jets symmetric, QCD unbalanced

Soft gluon radiation leads toasymmetric splittings

W/Z → qq̄ decays tend to sharemomentum more equally betweendecay products

Apply a more stringent√

y ≥ 0.45cut on the subjet momentumbalance

Another powerful cut!εsignal ≈ 70%εbackground ≈ 30%

Cuts optimised using MC, using awide mass window,60 GeV < mjet < 110 GeV

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W' WZ (m→EGM W'

Pythia QCD dijet

| < 1.2jj

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< 110 GeVj m≤60


Tools: Ghost matched jets4 Number of tracks ghost matched to the unfiltered jet

More hadronic activity in QCD jets

Emission of hard gluon dominatesafter mass/asymmetry cuts

Expect increased hadronic activityfrom gluon

Use the number of ghostassociated ungroomed tracks, ntrk,as a proxy for hadronic activity,[arXiv:0802.1188]

Apply ntrk ≤ 30 cut

Efficiency after mass/asymmetryεsignal = 83± 7%εbackground ≈ 65%

Very hard to model in MC

Cuts optimised using V+jetsenriched data CREfficiency calibrated in this CR

trkJet ungroomed n

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Pythia QCD dijet

| < 1.2jj

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< 110 GeVj m≤60 > 0.45 y



Modelling the Background

After trying to kill the background we now arrive at the point of modelling itMC statistics needed to properly model the high mJJ tail are prohibitively large

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Significance (stat)



No boson tagging

[TeV]jjm1.5 2 2.5 3 3.5

Sig

nific

ance

2−024

Assume a steeply and smoothly fallingdistribution models the background

Any resonance should be narrow, thus onlyaffect a few bins

Use a parametric function to model thebackground from the data

dndx

= p1(1− x)p2−ξp3 xp3

Where,x = mJJ/

√s

mJJ is the dijet invariant mass,p1 is a normalisation factor,p2 and p3 are dimensionless shapeparametersξ is a dimensionless constant chosen afterfitting to minimise the correlations betweenp2 and p3




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No boson tagging

[TeV]jjm1.5 2 2.5 3 3.5

Sig

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Sample χ2/nDOF ProbabilityPythia dijet events 24.6/22 0.31Herwig++ dijet events 15.9/22 0.82Data with 110 < mj1 ≤ 140 GeV and 40 < mj2 ≤ 60 GeV 12.1/11 0.79Data with 40 < mj ≤ 60 GeV for both jets 19.8/13 0.56Data with 110 < mj ≤ 140 GeV for both jets 5.0/6 0.91




dndx

= p1(1− x)p2−ξp3 xp3

Error taken from errors on functionalparameters

Fit tested on,Raw dataPYTHIA/HERWIG MCMass sideband data CRs

Alternate fit functions give similar results35 / 35 Alex Martyniuk BSM searches at ATLAS



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< 60 GeVj

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= p1(1− x)p2−ξp3 xp3






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< 60 GeVj1,j2

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= p1(1− x)p2−ξp3 xp3






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= p1(1− x)p2−ξp3 xp3




Systematic uncertainties: Shape

Background: Taken from the uncertainties on the fit parametersSignal: Various systematics affect the signal reconstruction and selectionefficiency

Shape systematics:The jet pT and jet mass scaleuncertainties determined by thetrack/calo double ratio technique

For example for a variable x,

xdatatrack/x

datacalo

xMCtrack/x

MCcalo

Applied as a Gaussian with µ = 1 and σequal to the observed uncertainty

jet pT scale: 2%jet mass scale: 3%

An uncertainty on the jet pT resolution of20% is applied as an additionalsmearing on top of the nominal 5%

) [GeV]2

, m1

max(m0 20 40 60 80 100 120 140 160

Jets

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BDRS-A| < 1.2

jjy∆|| < 2.0η|

A < 0.15 >= 0.45

fy

< 30trkn

qqqq→ WZ →W'(1.4 TeV)

NominalJMS upJMS downJMR

Source Uncertainty Constraining pdfJet pT scale 2% G(αPT|1, 0.02)

Jet pT resolution 20% G(σrE | 0, 0.05×√1.22 − 12)

Jet mass scale 3% G(αm|1, 0.03)


Systematic uncertainties: Normalisation

Background: Taken from the uncertainties on the fit parametersSignal: Various systematics affect the signal reconstruction and selectionefficiency

Normalisation systematics:Large uncertainty on the ntrk cutevaluated in the data driven V+jetsstudy used to define the efficiency of thecut

Jet mass scale affects both shape andnormalisation strongly√

y scale evaluated using the doubleratio method

Resolutions taken as 20% smearingsShower model evaluated by comparingMC showered by PYTHIA or HERWIG

PDF4LHC method used to evaluatePDF uncertainties

ATLAS luminosity uncertaintyassumed

) [GeV]2

, m1

min(m0 20 40 60 80 100 120 140 160

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fy

< 30trkn

qqqq→ WZ →W'(1.4 TeV)

NominalJMS upJMS downJMR

Source UncertaintyEfficiency of the track-multiplicity cut 20.0%

Jet mass scale 5.0%Jet mass resolution 5.5%

Subjet momentum-balance scale 3.5%Subjet momentum-balance resolution 2.0%

Parton shower model 5.0%Parton distribution functions 3.5%

Luminosity 2.8%


Selection overlapsComparing the effect of applying all signal selections at once, and the sameflavour selections at once

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[TeV]jjm1.5 2 2.5 3 3.5

Sig

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What do these events look like? Dramatic!


What do these events look like? Energetic!


Digging deeper into the jets....These jet event displays take a bit more explanation, but offer a powerfulinsight into the analysis jets

The ATLAS detector volume isshown unfolded in y and φ

Inner detector track positions areshown as crosses

Black Tracks: From primaryvertexBlue Tracks: From secondaryvertices

Calorimeter deposits are displayedon the rainbow scale

The outlines of the CA 1.2 jets areshown

Black: Leading pT jetMauve: Sub-leading jet

Grey area: Sub-jets after filtering

y-4 -3 -2 -1 0 1 2 3 4

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Run: 203027 Event: 5303984


Digging deeper into the jets....

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ATLAS = 8 TeVs

Run: 201489 Event: 75855145

What do we see here?Subjets are highly collimatedPV tracks are highly correlated with the selected sub-jetsEnergy deposits concentrated in the sub-jetPile-up tracks/deposits sparsely distributed over the eventsSuccessfully picked the boson out of the pileup?


Time to cross-check.....

Deviations from the expected background, especially ones at the tail of the datadistribution, mean one thing for physicists....

What on Earth did we do wrong?Try to evaluate any possible issues with the analysisOperation Cross-check beginsLook for mistakes, bugs or shaping effects in:

Detector/data taking effectsJet reconstruction effectsEvent selection effects

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From E. Kajomovitz35 / 35 Alex Martyniuk BSM searches at ATLAS


Started trawling throughSR/CR kinematic distributions,looking for unusual features inthe signal regions

Look at the effect of single cutson the distribution

Look at the effect of N − 1 cutson the distribution

Is one cut driving all of thedeviation?

Many, many, many..... more,you can only get so muchapproved...

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Did we find any errors?

In so many cross-checks, yes,bugs were found and fixed

Always attempted to shield thedata from any possible biasesby using control regions to test

After almost a year and a halfof scrutiny by theanalysers/Exoticsgroup/ATLAS we found nomajor issues

Therefore we continue topublish the final results

Run-2 was looming!


X →WW limits



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Exclusion of gravitonproduction at no masses

Deviation from thebackground observable ataround 2.1 TeV

Benchmark BulkRandall-Sundrum gravitonσ × B shown forcomparison purposes


X → ZZ limits



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Exclusion of gravitonproduction at no masses

Broad deviation from thebackground observable ataround 2 TeV

Benchmark BulkRandall-Sundrum gravitonσ × B shown forcomparison purposes


Are we alone? ATLAS searchesP

resc

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ATLAS resolved dijetsearch [arXiv:1407.1376],nothing seen 4

ATLAS resolved Run-2dijet searchATLAS-CONF-2015-042,nothing seen 4

ATLAS semi-leptonicsearch W (lν)Z (jj)[arXiv:http://1503.04677],using similar BDRS-A CA1.2 reconstruction, intail/nothing seen 4

ATLAS semi-leptonicsearch W (jj)Z (ll)[arXiv:1409.6190], usingsimilar BDRS-A CA 1.2reconstruction, intail/nothing seen 4






Are we alone? ATLAS searches

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ATLAS Preliminary-1=13 TeV, 80 pbs

DataBackground fitBumpHunter intervalBlackMax, m = 4.0 TeVBlackMax, m = 5.0 TeV




ATLAS semi-leptonicsearch W (jj)Z (ll)[arXiv:1409.6190], usingsimilar BDRS-A CA 1.2reconstruction, intail/nothing seen 435 / 35 Alex Martyniuk BSM searches at ATLAS





Are we alone? ATLAS searchesE

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0.60.8

11.21.4










Are we alone? Across the ring....CMSCMS dijet search[arXiv:1501.04198], blip in2-btag at 2 TeV? Trick ofthe eye? 4

CMS run-2 dijet search[CMS-PAS-EXO-15-001],nothing 4

CMS WR search[arXiv:1407.3683], excessat 2 TeV in eejj channelonly 42�

CMS WW/WZ/ZZsemi-leptonic search[arXiv:1405.3447], intails/nothing seen 4

CMS WW/WZ/ZZ fullyhadronic search[arXiv:1405.3447], usesn-subjettiness, broad blipat ≈ 1.8TeV 42�



https://cds.cern.ch/record/2048099?ln=en

http://lanl.arxiv.org/abs/1407.3683



Are we alone? Across the ring....CMS

Dijet Mass (GeV)1500 2000 2500 3000 3500 4000 4500 5000 5500

[pb

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QCD MC

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| < 1.3ηΔ| < 2.5, |η|> 1.1 TeVjjM

Wide Jets

(13 TeV)-142 pb

CMSPreliminary

Dijet Mass [GeV]1500 2000 2500 3000 3500 4000 4500 5000 5500

σ(D

ata-

Fit)/

-3-2-10123

CMS dijet search[arXiv:1501.04198], blip in2-btag at 2 TeV? Trick ofthe eye? 4











Are we alone? Across the ring....CMSCMS dijet search[arXiv:1501.04198], blip in2-btag at 2 TeV? Trick ofthe eye? 4











bsm searches at atlas€¦ · the atlas susy, exotics and higgs groups search for a wide range of...

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