2017. 4. 3 DM@LHC2017University of California Irvine

Mono-jet searches

Osamu JinnouchiTokyo Institute of Technology

on behalf of ATLAS and CMS Collaborations

Mono-jet signature

• One of the highest sensitivity signatures for BSM, esp. for DM searches• Search for (broad) excess in high ETmiss (MET) region

precise background estimation is vital• ATLAS: Phys. Rev. D94 (2016) 032005 13TeV (3.2 fb-1 taken in 2015)• CMS : PAS EXO-16-037 (submitted to JHEP) 13TeV (12.9 fb-1 taken in 2016)

2

METJET logN

Signal

Background

0 ETmiss

This talk reviews the similarity & difference of the two searches

ATLAS MET

JET

formono-Vanalysisthereisaseparatepaperhttps://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/EXOT-2015-08/

Mono-jet Physics Model for WIMP DM

• Both experiments interpret results with Simplified modelsbased on the suggestion from DM-Forum/Working Group to harmonize the models initial report: https://arxiv.org/abs/1507.00966

• simplified model described by 4 parameters• mDM, mMED, gq, gDM(𝛘) • minimal mediator width (no other invisible channel)

• ISR jet + s-channel axial vector mediator (ATLAS) • ISR jet + axial-vector/vector/scalar/pseudo-scalar mediators (CMS)

3

(AorV/S/P)

SearchforpairproducedDMwithISRjetwhichisusedtotagtheevent

JET

Mediator

mDM

mMEDgq gDM(χ) MET

Other Physics Model for mono-jet

• Large Extra dimensions (ADD)• production of KK tower of

massive graviton modes• escape detection → MET• associating with high-pT jet

• Compressed SUSY scenario• squark pair production with

relatively small mass gap• soft quark jets, MET →

hard to detect out of QCD multi-jet BG• hard ISR jet + boosted squark

pair (large MET)

4

JET

MET

JET

MET

JET

MET

5

The event selection and backgrounds

Baseline Event Selection Summary

• Jets: baseline : pT>20 GeV, |η|<2.8, JVT cut(pile up rejection), anti-kT R=0.4 based on topological clusters (ATLAS), particle flow (CMS) signal : pT>30 GeV

• Electrons : baseline : pT>20(10) GeV, loose identification, |η|<2.47 (2.5) signal : baseline + tight identification + IP cuts + track based isolation

• Muons : baseline : pT>10(10) GeV, medium id, |η|<2.5 (2.4) signal : baseline + IP cuts• (CMS) photon: pT>15 GeV tau : pT>18 GeV used for event veto• ETmiss (HTmiss) : base line objects and track soft term, computed without baseline muons

(muons as invisible)

6

ATLAS CMS

Trigger ETmiss>70GeV

ETmiss,HTmiss>90,100,110GeV

LeadingJet pT>250GeV,|η|<2.4 pT>100GeV,|η|<2.5ETmiss >250GeV >200GeVmultijetBGrejection

ΔΦ(pTmiss,jets(1,2,3,4))>0.4NJETS(pT>30GeV)≤4

ΔΦ(ETmiss,jets(1,2,3,4))>0.5NJETScouldbeany

NCBrejection

Leadingjet|η|<2.4passestightcleaning

jetenergycharged>10%,neutral<80%

jetpT>250GeV

MET>250GeV

e&μveto

Upto3otherjets(pT>30GeV)

>0.4

ObjectdefinitionsN.B.ATLASselectionforillustrationpurpose

N.B.valuesinparenthesesareonesforCMS

• Dominant BG: MC+globalfit

• Z (νν) + jets• irreducible, dominant esp. in high MET

• W(lν) + jets • irreducible when leptons are out of acceptance

or from the detector inefficiency

• Other BG:• Z/γ*(ll) + jets : MC+globalfit(ATLASusesMCforZ/γ*(ee))　　　　　　• ttbar, single top, di-boson : MConly

• QCD multi-jet, Non-collision BG : datadrivenestimate

ATLAS CMS

Background composition overview 7

Others 6%

Z+jets 58%

W+jets 35%

Others 11%

Z+jets 67%

W+jets 22%

Others 3%

Z+jets 63%

W+jets 34%

Others 3%

Z+jets 81%

W+jets 16%

lowM

ETcut

(250

GeV

)highM

ETcut

(750

GeV

)

8

The Analysis Strategy

Strategy for mono-jet in ATLAS 9

7exclusiveSRs

SRveto on baseline leptons

singleelectronCR• exactly one isolated e, no μ• target backgrounds:

singlemuonCR• exactly one μ, no e

30 GeV <MT<100GeV• target BGs:

di-muonCR• exactly two μ, no e

66 GeV <Mμμ<116 GeV• target BG:

performglobalfitandderive3scalefactorstonormalizeEWbackgrounds

• Signal Regions

• SR (7 MET bin) accompany 3 x CR each

W (eν )+jets, W (τν )+jets, Z γ * (ττ )+jets

W (µν )+jets, Z(νν )+jetsZ γ * (µµ)+jets

Analysis strategy in ATLAS (cont’d) 10

Z(νν )+ jets

3xETmissdependentnormalizationfactors()usedtoconstrainttheEWbackgroundsineachCRfW→e

bin , fW→µbin , fZ→µµ

bin

ControlRegions backgroundprocess norm.factorW→eν(single-e)　W→μν(single-μ)Z→μμ(di-muon)

W (eν )+jets, W (τν )+jets, Z γ * (ττ )+jets

W (µν )+jets, Z(νν )+jetsZ γ * (µµ)+jets

fW→ebin

fW→µbin

fZ→µµbin

MCratio(Sherpa)

ttbar,etcW→μν(single-μ)CR

• transferdistributionfromW(μν)CR• statisticalpower(7xZ(μμ)+jets),partialsystematiccancelation

W,ZbosoneventsaregeneratedwithSherpa-2.1.1,upto2(4)-partonatNLO(LO)

Single lepton CRs in ATLAS (post fit) 11

dataandpredictionforIM1(MET>250GeV)selectionafterthefitinexclusiveMETbins,grayband:stat.+syst.errorsafterthefit

• Objective : performed global fit to derive scale factor for EW backgrounds• ETmiss calculation includes EM cluster, and not corrected for muon

W (eν )+jets, W (τν )+jets, Z γ * (ττ )+jetsW(eν)CR W(μν)CR

W (µν )+jets, Z(νν )+jets

W(eν)CR W(μν)CR

Z(μμ)CR

Di-muon CR in ATLAS (post fit)• objective: estimate Z(μμ)+jets in SR

ETmiss is not corrected for muons (muons considered as invisible)• performed global fit to derive scale factor for EW backgrounds

12

N(signalmuon)=2,N(baseelectron)=066GeV<mμμ<116GeV

dataandpredictionforIM1(MET>250GeV)selectionafterthefitinexclusiveMETbinsgrayband:stat.+syst.errorsafterthefitNumberofjets

Z γ * (µµ)+jets

Z(μμ)CR

Other backgrounds in ATLAS

• Z(ee)+jets• ttbar, single top, di-boson

13

MCbasedestimation

Multi-jetBG• fake ETmiss, from mis-measured jets • estimated from jet smearing &

inverted dΦ (jet, MET)• negligible in high MET

NCB(NonCollisionBG)• Cosmic or Beam-induced background• jet cleaning reduction < 0.1 %• residual events can be tagged by

matching calorimeter and muon segment• almost negligible contributions in SR

\leading jet 3< 2< 1< 0 1 2 3

Even

ts

210

310

410

510

610

710Data 2015

Standard Model

ATLAS-1 = 13 TeV, 3.2 fbs

Tight jet cleaning not applied to data

>250GeV, lepton vetomissT

>250GeV, EjetT

p

[Eve

nts/

GeV

]m

iss

TdN

/dE

1<10

1

10

210

310

410 Data 2015Standard Model

) + jetsii AZ() + jetsi eAW() + jetsiµ AW() + jetsio AW(

ll) + jetsAZ( + single toptt

Dibosonsmultijets

ATLAS-1 = 13 TeV, 3.2 fbs

Multijets Control Region>250 GeVmiss

T>250 GeV, E

Tp

[GeV]missTE

300 400 500 600 700 800 900 1000

Dat

a / S

M

1

2

Analysis strategy in CMS

• Signal region • mono-jet (& mono-V category)

• 5x Control regions for each SR• 5 CRs to constrains 2 major BGs (Z(νν)+jets, W(lν)+jets)

14

Z(νν )+ jets BG W (lν )+ jets BG

γ + jets CR

×Riγ

×RiZ

Z(ll) CR l = e,µ

µiW→lν → fi (θ ) ⋅µi

Z→νν

x20stats.

poorstatsinhighMET

W (lν ) CR l = e,µ×Ri

W

passtheV-tag(AK8,mass,etc)seebackupslide

Analysis strategy in CMS

• Transfer factor to translate recoil (in CR) to missing ET (in SR)• Global likelihood fit simultaneously to SR+5CR regions in all ETmiss bins

15

µi :yields Ri : transfer factorµiW→lν → fi (θ ) ⋅µi

Z→νν

γ + jets CR

Z(ll)+ jets CR

W (lν )+ jets CR

SR

constraintsfromtransferfactors,onlyonefreeparametertofit

Transfer factors in CMS 16

Z(μμ)CR→Z(νν) γ+jetsCR→Z(νν)

factorization/renormalizationscale

W(μν)CR→W(lν)

W(lν)→Z(νν)

①

②

③④

① ②

③

④ fromDMWGpublicmeeting19Sep2016

eventsaregeneratedwithMadGraph(LO)andcorrectedtoNLO

CR distributions in CMS (1)

• post-fit predictions match well with data in all CRs

17

di-muonCR di-electronCR γ+jetsCR

CR distributions in CMS (2)

• post-fit predictions match well with data in all CRs

18

single-muonCR single-electronCR

Systematics uncertainties in ATLAS 19

• Z(ee)+jets• ttbar, single top, di-boson

Backgroundtheoreticaluncertainties

Experimentaluncertainties

• Normalization, factorization, PS-ME matching scale, PDFs• for Sherpa W/Z 1.1 - 1.3 %• for top backgrounds 2.7 - 3.3 %

• Diboson generator difference : 0.05 - 0.4% • Multi-jet background : 0.2 %

• jet, MET scale: 0.5 - 1.6 %• jet quality requirements, pile-up

description/correction to jet/MET : 0.2-0.9%• lepton ID, reconst Eff., energy scale/

resolutions : 0.1 -2.6 % in IM7• luminosity : 5 %• statistical uncertainties for CRs : 2.5 - 10 %

W/Z+jetsmodeling (Z(νν)inSR)

• lepton rec, eff, acceptance 3% flat uncertainties for all MET bins

• NLO EW radiative corrections : 1.9 % for IM1, 5.2% for IM7

Signaluncertainties• jet/MET reconstruction, energy scale,

resolution, luminosity • gluon radiation model: shower

parameters, αS, renom./factor. scale• jet quality requirement < 1%

Overalluncertainties(stat.+sys.):4.0%(IM1),6.8%(IM5),12%(IM7)

Systematics uncertainties in CMS 20

• Z(ee)+jets• ttbar, single top, di-boson

Backgroundtheoreticaluncertainties

Experimentaluncertainties

• top backgrounds : relative 10 % b-veto : 6%

• Diboson generator difference : relative 20 % b-veto : 2%

• Multi-jet background : relative 50-150%

• luminosity : 6.2 %• ETmiss modeling (jet energy scale) : 5%• lepton reconstruction : 1%

selection : 2%

W/Z/γ+jetsmodeling• γ+jets to Z+jets, W+jets to Z+jets

differential cross section ratios- renormalization (10-15%) - factorization (1-10%) - PDF (negligible)

• NLO EW corrections- γ+jets (2-14%), W+jets (1-9%)

21

The Results

Even

ts /

50 G

eV

2<10

1<10

1

10

210

310

410

510

610

710 ATLAS-1 = 13 TeV, 3.2 fbs

Signal Region>250 GeV miss

T>250 GeV, E

Tp

Data 2015Standard Model

) + jetsii AZ() + jetsio AW() + jetsiµ AW() + jetsi eAW(

ll) + jetsAZ(Dibosons

+ single toptt) = (350, 345) GeV0

r¾, b~m()= (150, 1000) GeV

med, M

DM(m

=5600 GeVD

ADD, n=3, M

[GeV]missTE

400 600 800 1000 1200 1400

Dat

a / S

M

0.5

1

1.5

Even

ts /

50 G

eV

2<10

1<10

1

10

210

310

410

510

610

710 ATLAS-1 = 13 TeV, 3.2 fbs

Signal Region>250 GeV miss

T>250 GeV, E

Tp

Data 2015Standard Model

) + jetsii AZ() + jetsio AW() + jetsiµ AW() + jetsi eAW(

ll) + jetsAZ(Dibosons

+ single toptt) = (350, 345) GeV0

r¾, b~m()= (150, 1000) GeV

med, M

DM(m

=5600 GeVD

ADD, n=3, M

[GeV]T

Leading jet p400 600 800 1000 1200 1400

Dat

a / S

M

0.5

1

1.5

Results (Signal Region) in ATLAS 22nosignificantexcessobserved

Even

ts

500

1000

1500

2000

2500

Data 2015Standard Model

) + jetsii AZ() + jetsi lAW(

ll) + jetsAZ( + single toptt

Dibosonsmultijets + NCB

ATLAS-1 = 13 TeV, 3.2 fbs

Selection: EM4

) CRi eAW( ) CRiµ AW( ) CRµµ AZ( SR

Dat

a/SM

0.8

1

1.2

Results in ATLAS 23

EM1(ETmiss = 250 − 300 GeV) EM4(ET

miss = 400 − 500 GeV) EM7(ETmiss > 700 GeV)

post-fit predictions match well with data in SR/CRs

• modelindependent95%C.L.upperlimitson -signalevents-visiblecrosssectionsforeachETmissbin• 553―19fbobtained

Even

ts

2000

4000

6000

8000

10000

12000 Data 2015Standard Model

) + jetsii AZ() + jetsi lAW(

ll) + jetsAZ( + single toptt

Dibosonsmultijets + NCB

ATLAS-1 = 13 TeV, 3.2 fbs

Selection: EM1

) CRi eAW( ) CRiµ AW( ) CRµµ AZ( SR

Dat

a/SM

0.8

1

1.2

Even

ts

20

40

6080

100

120140

160

180200

Data 2015Standard Model

) + jetsii AZ() + jetsi lAW(

ll) + jetsAZ( + single toptt

Dibosonsmultijets + NCB

ATLAS-1 = 13 TeV, 3.2 fbs

Selection: IM7

) CRi eAW( ) CRiµ AW( ) CRµµ AZ( SR

Dat

a/SM

0.8

1

1.2

W (eν )CR

W (µν ) CR

Z(µµ)CR

SR

W (eν )CR

W (µν ) CR

Z(µµ)CR

SR

W (eν )CR

W (µν ) CR

Z(µµ)CR

SR

Even

ts /

GeV

2−10

1−10

1

10

210

310

410

510 Data

)+jetsννZ(

)+jetsνW(l

WW/ZZ/WZ

Top quark

+jetsγZ(ll)+jets,

QCD

= 125 GeVH

Higgs Invisible, m

= 1.6 TeVmedAxial-vector, m

(13 TeV)-112.9 fb

CMSmonojet

Dat

a / P

red.

0.5

1

1.5

[GeV]missTE

200 400 600 800 1000 1200

pred

σ(D

ata-

Pred

.)

2−02

Even

ts /

GeV

2−10

1−10

1

10

210

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510 Data

)+jetsννZ(

)+jetsνW(l

WW/ZZ/WZ

Top quark

+jetsγZ(ll)+jets,

QCD

= 125 GeVH

Higgs Invisible, m

= 1.6 TeVmedAxial-vector, m

(13 TeV)-112.9 fb

CMSmonojet

Dat

a / P

red.

0.5

1

1.5

[GeV]missTE

200 400 600 800 1000 1200

pred

σ(D

ata-

Pred

.)

2−02

Results (Signal Region) in CMS 24

postcombinedfitonlyinCRs

Thelast

bin

isoverflo

wbin

postcombinedfitbothinCRsandSR(assumingnoDMsignal)

grayband:postfituncertainty nosignalexcess(smallnon-significantdeficits)

25

DM Interpretations

[GeV]Am0 500 1000 1500 2000

[GeV

]r

m

0

200

400

)expm 1 ±Expected limit (

)PDF, scaletheorym 1 ±Observed limit (

Perturbativity Limit

Relic Density

ATLAS -1 = 13 TeV, 3.2 fbs

Axial Vector MediatorDirac Fermion DM

= 1.0r

= 0.25, gqg95% CL limits

r

= 2

mAm

DM interpretation (Mediator mass vs. WIMP (DM) mass)

• In ATLAS (L=3.2 fb-1), observed (expected) limit on Mediator mass at 1.0 TeV (1.2 TeV) for WIMP mass below 250 GeV (300 GeV) at 95% CL

• In CMS (L=12.9 fb-1), observed (expected) limit on Mediator mass at 1.95 TeV (1.7 TeV) for WIMP mass below 450 GeV (600 GeV) at 95% CL

26

Axialvectormediatorgq=0.25,gDM=1.0

[GeV]rm1 10 210 310 410

]2-p

roto

n) [c

mr (

SDm

42<10

39<10

36<10

33<10

30<10XENON100LUXPICO-2LPICO-60Axial Vector Mediator

90% CL limits

Dirac Fermion DM = 1.0

r = 0.25, gqg

ATLAS -1 = 13 TeV, 3.2 fbs

[GeV]DMm1 10 210

]2 [c

mD

M-p

roto

nSD σ

44−10

43−10

42−10

41−10

40−10

39−10

38−10

37−10

36−10

35−10

34−10

33−10

CMS median exp. 90% CLCMS obs. 90% CLPICO-60PICO-2L

-τ+τIceCube -τ+τSuper-K

(13 TeV)-112.9 fb

CMS = 1

DM = 0.25, g

qAxial-vector med, Dirac DM, g

DM interpretation (DM-nucleon scattering cross-sections) 27

Axialvectormediatorgq=0.25,gDM=1.0

for WIMP masses below 10 GeV with 90% CL, • In ATLAS, WIMP-nucleon spin dependent cross sections above 10-42cm2 excluded• In CMS, WIMP-proton spin dependent cross sections above 10-43cm2 excluded

LUX : Phys. Rev. Lett. 116, 161302 (2016), XENON100 : Data, Phys. Rev. Lett. 1110 21301 (2013)

PICO-2L : Phys. Rev. D93 (2016) 061101, PICO-60 : Phys. Rev. D 93, 052014 (2016)

IceCube : JCAP 04 (2016) 022, Super Kamiokande : Phys. Rev. Lett. 114 (2015) 141301

excludedregionexcludedregion

Other interpretations in ATLAS

• SUSY: interpreted in terms of stop pair production in a compressed scenarios stop masses below 323 GeV are excluded in 95% C.L. (sbottom/squark mass below 323/608 GeV are excluded in 95% C.L.)

• ADD Large Extra Dimension Model: 6.58 TeV at n=2 is excluded

• significant improvement against Run-1 result

28

Number Of Extra Dimensions

2 3 4 5 6

Low

er L

imit

[TeV

]D

M

3

4

5

6

7

8 -1=13 TeV, 3.2 fbs

All limits at 95% CL

ATLAS )expm 1 ±Expected Limit (

Observed Limit

Obs. Limit (after damping)

-1fb TeV, 20.3 = 8sATLAS

[GeV]1t

~m260 280 300 320 340 360 380 400 420 440

[GeV

]10 r¾

m

150

200

250

300

350

400

450

-1 = 13 TeV, 3.2 fbs

10

r¾ cA1t~ production, 1t

~1t

~

All limits at 95% CL

ATLAS

)theorySUSYm1 ±Observed limit (

)expm1 ±Expected limit (

= 8 TeVsATLAS

c + m0

1r¾ < m1t~m

W + mb + m

01r¾ > m

1t~m

Other interpretations in CMS

• WIMP-nucleon spin independent cross sections above 10-42cm2

for WIMP masses below 10 GeV excluded at 90% C.L. with Vector type mediator• WIMP-nucleon spin independent cross sections above 10-45cm2

for WIMP masses below 10 GeV excluded at 90% C.L. with Scalar type mediator

29

excludedregion

Vectormediatorgq=0.25,gDM=1.0

excludedregion

Scalarmediatorgq=1.0,gDM=1.0

Summary of mono-jet searches

• Mono-jet is one of the most powerful channel in searching for DM by collider experiments

• ATLAS and CMS performed searches for mono-jet signature using different approaches

• No excesses were observed, limits were set accordingly

• The results were interpreted with DM models, limits on

• mediator & DM masses• nucleon scattering cross sections, were obtained

30

31

Extra materials

V-tagging in CMS

• Events are classified into mono-V or mono-jet• Mono-V selection:• MET > 250 GeV• leading AK8 (anti-kT distant parameter 0.8) jet > 250 GeV• jet mass between 65 and 105 GeV• after pruning

• τN (N sub-jettiness variable) : τ2/τ1<0.6• Mono-jet • the events which failed mono-V selection

32

Event yields in SRs (ATLAS) 33

Event yields in SRs (CMS) 34

Systematic error direct comparison 35