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
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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