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

2

Introduction

• From cosmological observations, 85% of the matter comprised of dark matter (DM)

• Collider approach: DM production by colliding SM particles at high energies

2

Bullet Cluster (Image: NASA)


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

3

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.


General strategy

4

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.


CMS searches for dark matter• Focus will be on 13 TeV (2015 dataset) preliminary results

• Other CMS dark matter results

5

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)


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


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

7

Vector mediator Axial-vector mediator

EXO-16-013


Mono-jet/jets/W/Z: interpretation• Results can be recast in terms of nucleon-DM scattering cross section• Compare to direct detection search limits

8

EXO-16-013

Vector mediator Axial-vector mediator


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

9

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


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

10

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


= 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



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

11


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

12

B2G-15-007

Scalar mediator Pseudoscalar mediator


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

13

t

V

g

ui

t

χ̄

χ


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

14

EXO-16-017 New


CMS dark matter search summary

15

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


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

16

Backup


Monophoton: interpretation

18

= 1DM

g = 0.25, qgVector, Dirac, Observed 90% CLMedian expected 90% CLLUX


[GeV]DMm1 10 210

]2 (D

M-n

ucle

on) [

cmSI

σ

-4610

-4510

-4410

-4310

-4210

-4110

-4010

-3910

-3810

-3710

-3610

-3510

-3410

-3310

= 1DM

g = 0.25, qgAxial vector, Dirac, Observed 90% CLMedian expected 90% CLPICO-60PICO-2L


[GeV]DMm1 10 210

]2 (D

M-n

ucle

on) [

cmSD

σ-4210

-4110

-4010

-3910

-3810

-3710

-3610

Documents

Searches for Dark Matter Production with CMS