Searches for Dark Matter Production with CMS
Transcript of Searches for Dark Matter Production with CMS
Searches for Dark Matter Production with CMS
Bodhitha Jayatilaka Fermilabon behalf of the CMS Collaboration
LHCP 2016 Lund, Sweden17 June 2016
LHCP2016, 17-Jun-2016 Bo Jayatilaka
The search for dark matter• Existence of dark matter is well established
from cosmological observations• Exact nature of it is unknown
• Ways to look for (particle) DM• Direct searches via DM-nucleon scattering• Indirect searches via DM annihilation• Search for production of DM at colliders
• LHC provides a prime laboratory for production of DM• Search for evidence of DM production along
with (visible) SM particles• Can characterize DM interaction as function
of spin/parity, coupling, etc
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Introduction
• From cosmological observations, 85% of the matter comprised of dark matter (DM)
• Collider approach: DM production by colliding SM particles at high energies
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Bullet Cluster (Image: NASA)
LHCP2016, 17-Jun-2016 Bo Jayatilaka
Benchmark signatures for LHC DM searches• Searches for DM at the LHC look for ETmiss+X
• X = jet, W, Z, γ, H, tt, bb, t, etc.• Run 2: Adopt simplified models to interpret results (arXiv:1507.00966)
• Assume new massive particle which mediates DM-SM interaction• DM particle is a Dirac fermion χ• Keep to a minimal set of parameters
• Mmed, mχ, gSM, gDM, Γmed
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18 atlas+cms dark matter forum
V, A(Mmed)
q̄
q
c̄(mc
)
c(mc
)g
gq gDM
Figure 2.1: Representative Feynmandiagram showing the pair productionof Dark Matter particles in associationwith a parton from the initial state viaa vector or axial-vector mediator. Thecross section and kinematics dependupon the mediator and Dark Mattermasses, and the mediator couplings toDark Matter and quarks respectively:(Mmed, m
c
, gc
, gq).
Lvector = gq Âq=u,d,s,c,b,t
Z0µ
q̄g
µq + gc
Z0µ
c̄g
µ
c (2.1)
Laxial�vector = gq Âq=u,d,s,c,b,t
Z0µ
q̄g
µ
g
5q + gc
Z0µ
c̄g
µ
g
5c. (2.2)
The coupling gq is assumed to be universal to all quarks. It is alsopossible to consider other models in which mixed vector and axial-vector couplings are considered, for instance the couplings to thequarks are axial-vector whereas those to DM are vector. As men-tioned in the Introduction, when no additional visible or invisibledecays contribute to the width of the mediator, the minimal widthis fixed by the choices of couplings gq and g
c
. The effect of largerwidths is discussed in Section 2.5.2. For the vector and axial-vectormodels, the minimal width is:
GVmin =
g2c
Mmed
12p
1 +2m2
c
M2med
!
bDMq(Mmed � 2mc
) (2.3)
+ Âq
3g2qMmed
12p
1 +2m2
q
M2med
!
bqq(Mmed � 2mq),
GAmin =
g2c
Mmed
12p
b
3DMq(Mmed � 2m
c
) (2.4)
+ Âq
3g2qMmed
12p
b
3qq(Mmed � 2mq) .
q(x) denotes the Heaviside step function, and b f =
r
1 � 4m2f
M2med
is the velocity of the fermion f with mass m f in the mediatorrest frame. Note the color factor 3 in the quark terms. Figure 2.2shows the minimal width as a function of mediator mass for bothvector and axial-vector mediators assuming the coupling choicegq = g
c
= 1. With this choice of the couplings, the dominant con-tribution to the minimal width comes from the quarks, due to thecombined quark number and color factor enhancement. We specif-ically assume that the vector mediator does not couple to leptons.If such a coupling were present, it would have a minor effect in in-creasing the mediator width, but it would also bring in constraintsfrom measurements of the Drell-Yan process that would unneces-sarily restrict the model space.
LHCP2016, 17-Jun-2016 Bo Jayatilaka
General strategy
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t
V
g
ui
t
χ̄
χ
1. Select events
Large ETmiss
“Tag” with recoilingobject
2. Constrain backgrounds
Even
ts /
GeV
-310
-210
-110
1
10
210 Data
SM backgrounds (pre-fit)
SM backgrounds (post-fit)
QCD
VV
ll→Z
Single top
tt
νl→W
Single muon W CR (13 TeV)-12.3 fb
CMS Preliminary
Recoil [GeV]300 400 500 600 700 800 900 1000
Dat
a / P
red.
00.5
11.5
2pre-fit post-fit
Even
ts /
GeV
-310
-210
-110
1
10
210 Data
SM backgrounds (pre-fit)
SM backgrounds (post-fit)
ll→Z
QCD
VV
Single top
tt
CRtSingle muon t (13 TeV)-12.3 fb
CMS Preliminary
Recoil [GeV]300 400 500 600 700 800 900 1000
Dat
a / P
red.
00.5
11.5
2pre-fit post-fit
3. Search high ETmiss
4. Find excess5. ????6. Profit!
OR 4.
LHCP2016, 17-Jun-2016 Bo Jayatilaka
CMS searches for dark matter• Focus will be on 13 TeV (2015 dataset) preliminary results
• Other CMS dark matter results
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X Dataset CMS Doc AvailableJets,W/Z(qq) 13 TeV, 2.3/fb EXO-16-013 April 2016
γ 13 TeV, 2.3/fb EXO-16-014 June 2016bb 13 TeV, 2.2/fb B2G-15-007 March 2016
t (hadronic) 13 TeV, 2.3/fb EXO-16-017 June 2016
X Dataset CMS Doc PublishedDijet 8 TeV, 20/fb EXO-14-004 Submitted to JHEPZ(ll) 8 TeV, 20/fb EXO-12-054 PRD 93, 052011 (2016)
tt(l+jets) 8 TeV, 20/fb B2G-14-004 JHEP 06 (2015) 121t (hadronic) 8 TeV, 20/fb EXO-12-022 PRL 114, 101801 (2015)
γ 8 TeV, 20/fb EXO-12-047 PLB 755 (2016) 102W(lν) 8 TeV, 20/fb EXO-12-060 PRD 91, 092005 (2015)
LHCP2016, 17-Jun-2016 Bo Jayatilaka
Mono-jet/jets/W/Z• Search for large ETmiss and ≥1 high-pT jets• Encompasses both monojet and mono-W/Z (decaying hadronically)• After basic ID, separate into two categories for each
• Mono-V: large-radius jets for highly boosted W/Z: [ETmiss,pTj1]> 250 GeV• Mono-jet: remaining events with ETmiss > 200 GeV, pTj1> 100 GeV
• Backgrounds dominated by Z(νν)+jets and W(lν)+jets• Veto events with isolated leptons or b-tags
• Fit background and signal predictions to ETmiss in data
6Monojet MonoV
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Mono-jet/jets/W/Z: results• No excess observed: set limits on cross section in simplified model
• Fix gq = gDM = 1 (direct comparison with 8 TeV) and scan in Mmed and mχ
• Mmed>1.3 TeV @90%CL
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Vector mediator Axial-vector mediator
EXO-16-013
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Mono-jet/jets/W/Z: interpretation• Results can be recast in terms of nucleon-DM scattering cross section• Compare to direct detection search limits
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EXO-16-013
Vector mediator Axial-vector mediator
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Monophoton• Search for large ETmiss and a photon
• Dark matter production with an ISR photon• Large extra dimension models with graviton production and a recoiling
photon• Select events with one fiducial photon with pT > 175 GeV and ETmiss > 170 GeV
• Angular separation between photon and ETmiss
• Primary background is Z(νν)+γ
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200 400 600 800 1000
Even
ts/G
eV
-310
-210
-110
1
10
(13 TeV)-12.3 fbPreliminary CMS
γ), ttντ, W(γ), Z(ll)νµ+jet, W(γ Beam-haloSpikes MisIDγ →jet
MisIDγ →electron γν l→γWγνν →γZ Bkg. uncertainty
ADD, MD=2TeV, n=5 Data
[GeV]γ
TE200 300 400 500 600 700 800 900 1000
Dat
a/SM
00.5
11.5
2 200 400 600 800 1000
Even
ts/G
eV
-310
-210
-110
1
10
(13 TeV)-12.3 fbPreliminary CMSγ), ttντ, W(γ), Z(ll)νµ+jet, W(γ Beam halo
Spikes MisIDγ →jet MisIDγ →electron γν l→γW
γνν →γZ Bkg. uncertaintyADD, MD=2TeV, n=5 Data
[GeV]TE200 300 400 500 600 700 800 900 1000
Dat
a/SM
0123
Photon ET ETmiss
LHCP2016, 17-Jun-2016 Bo Jayatilaka
Monophoton results• No excess observed: set limits on cross section in simplified model
• Fix gq = 0.25, gDM = 1 and scan in Mmed and mχ
• Mmed > 600 GeV @95%CL
• Place limits on EFT model with contact interaction of type γγχχ• Suppression scale Λ > 542 GeV @95%CL
• Exclude ADD Graviton production up to 2.35 TeV for n=6
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EXO-16-014 New
Vector mediator Axial-vector mediator ADD Graviton
THσ/
95% CL
σO
bserved
-110
1
10
210
THσ/
95% CL
σO
bserved
-110
1
10
210
-1 = 13 TeV, 2.3 fbsPreliminary CMS
= 1DM
g = 0.25, qgVector, Dirac, Observed 95% CLTheoretical uncertaintyMedian expected 95% CL
σ1±Expected
[GeV]medM100 200 300 400 500 600 700 800
[GeV
]DM
m
50
100
150
200
250
300
350
400TH
σ/95%
CLσ
Observed
-110
1
10
210
THσ/
95% CL
σO
bserved
-110
1
10
210
-1 = 13 TeV, 2.3 fbsPreliminary CMS
= 1DM
g = 0.25, qgAxial vector, Dirac, Observed 95% CLTheoretical uncertaintyMedian expected 95% CL
σ1±Expected
[GeV]medM100 200 300 400 500 600 700 800
[GeV
]DM
m
50
100
150
200
250
300
350
400
[TeV]DM1 1.5 2 2.5 3
Cro
ss s
ectio
n [fb
]
1
10
210
310
n=3, Theory LO 95% CL Obs. Limit
95% CL Exp. Limit σ1±Exp. Limit
σ2±Exp. Limit
-1 = 13 TeV, 2.3 fbsPreliminary CMS
LHCP2016, 17-Jun-2016 Bo Jayatilaka
DM+b/bb/tt• Search for DM recoiling against jets with b quarks
• Sensitive to tt+DM production as well• 1-tag: ETmiss> 200 GeV, tagged jet pT > 50 GeV, up to 1 additional jet• 2-tag: ETmiss> 200 GeV, two tagged jets pT > 50 GeV, up to 1 additional jet
• Recovers efficiency of tt+DM• In both cases, veto events with isolated leptons
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DM+b/bb/tt results• No excess seen: set limits combining both tag categories• Interpret as a function of scalar and pseudoscalar mediator masses
• Fix mχ=1 GeV
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B2G-15-007
Scalar mediator Pseudoscalar mediator
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Monotop• Search for single top quark and large ETmiss
• Sensitive to models producing DM+top via FCNC• Analogous to monojet but with FCNC
• Select events with ETmiss>250 GeV• Top decay products in boosted events merged into “fat jet”, pT > 250 GeV• b-tagged subjet, Jet mass: [110, 210] GeV, and τ3/τ2 to ID top quarks• Veto leptons and additional b-tags
• Dominant backgrounds are V+jets and ttbar
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t
V
g
ui
t
χ̄
χ
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Monotop results• No excess seen: set limits on FCNC model
• Exclude mediator masses up to 1.1 TeV @95%CL • Evaluated for aFC=bFC=0.1 (roughly gSM=0.1, gDM=1), mχ=100 GeV
• Extends previous monotop limits
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EXO-16-017 New
LHCP2016, 17-Jun-2016 Bo Jayatilaka
CMS dark matter search summary
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Maximal excluded mass [GeV]1 10 210 310 410
=1
q=g
DMPseudoscalar; g
t/tbDM + b
=1q
=gDM
Scalar; g t/tbDM + b
=1
q=g
DMPseudoscalar; g
)qDM + jets/V(q
=1q
=gDM
Scalar; g )qDM + jets/V(q
=0.1FC=b
FCFC Vector; a
DM + t
=0.25q
=1, gDM
Axial vector; g γDM +
=0.25
q=1, g
DMVector; g
γDM +
=1q
=gDM
Axial vector; g )qDM + jets/V(q
=1
q=g
DMVector; g
)qDM + jets/V(q
Mediator exclusion DM exclusion
-113TeV, 2.3fbEXO-16-01390%CL
-113TeV, 2.3fbEXO-16-01390%CL
-113TeV, 2.3fbEXO-16-01495%CL
-113TeV, 2.3fbEXO-16-01495%CL
-113TeV, 2.3fbEXO-16-01795%CL
-18TeV, 19.7fbEXO-12-05590%CL
-18TeV, 19.7fbEXO-12-05590%CL
-113TeV, 2.17fbB2G-15-00795%CL
-113TeV, 2.17fbB2G-15-00795%CL
CMS Preliminary Dark Matter Summary* - June 2016
*Observed limitsTheory uncertainties not included
spin 0 mediator
spin 1 mediator
= 300σ/σ
= 50σ/σ
LHCP2016, 17-Jun-2016 Bo Jayatilaka
Conclusions• CMS dark matter searches aim to leave no (collider-based) stone unturned• Standardized interpretation scheme and models
• Allows for straightforward comparison of results between experiments• Interpretations that compare to direct searches
• First set of Run 2 results now available • No signs of excess yet• Expect further results (including with 2016 data) in the coming months
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Backup
LHCP2016, 17-Jun-2016 Bo Jayatilaka
Monophoton: interpretation
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= 1DM
g = 0.25, qgVector, Dirac, Observed 90% CLMedian expected 90% CLLUX
-1 = 13 TeV, 2.3 fbsPreliminary CMS
[GeV]DMm1 10 210
]2 (D
M-n
ucle
on) [
cmSI
σ
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-4010
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= 1DM
g = 0.25, qgAxial vector, Dirac, Observed 90% CLMedian expected 90% CLPICO-60PICO-2L
-1 = 13 TeV, 2.3 fbsPreliminary CMS
[GeV]DMm1 10 210
]2 (D
M-n
ucle
on) [
cmSD
σ-4210
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-4010
-3910
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