Searches for dark matter at CMS and...

Searches for dark matter

at CMS and ATLAS

K. BierwagenJohannes Gutenberg University Mainz

On behalf of the ATLAS and CMS Collaboration

March 20, 2018

20.03.2018 K. Bierwagen - Moriond QCD 2018 2

Introduction

Astrophysical observations point to the existence ofDark Matter (DM)

Rotation curves Bullet Cluster CMB

Underlying nature of DM remains unknown

WIMP paradigm → Motivation to consider collider searches for DM


Dark Matter Signatures

Mono-photon Mono-jet

Mono-Higgs

Mono-W/Z

Mono-t/tt

A wide range of finalstates can be investigated

with the LHC

Mono-b/bb

For more details on dijetsearches see talks by

C. Gwilliam and D. Moran


Missing Transverse Energy


Search for DM with jets

Jet pT of 973 GeV

balanced by a ET

miss of 954 GeV

Largest ET

miss+X cross-section

at LHC

MET

signal

background

Search for high MET excess


Signal Region

CMS-EXO-16-048

JHEP 01 (2018) 126

> 0.4Up to 3additional jets(p

T>30 GeV)

Jet pT>250 GeV

|η|<2.4

MET > 250 GeV

e & μ veto

N.B. ATLAS selection for illustration purpose

Crucial to measure SMbackground precisely

https://link.springer.com/article/10.1007%252FJHEP01(2018)126


Backgrounds

● Main Backgrounds

– Z(vv)+jets: irreducible

– W(lv)+jets: irreducible whenleptons are out of detectoracceptance

● Backgrounds constrained indedicated control regions

● V+jet modeled at NNLO QCD& NLO EW– Includes theory predictions via

MC reweighting based on pT(V)

57% 38%

6%Other

Z+jets W+jets

72%

23%5%Other

Z+jets

W+jets

High METLow MET

59%37%

4%Other

Z+jetsW+jets

84%

11%6%

Other

Z+jets

W+jets

ATLAS

CMS

Lindert, J.M., Pozzorini, S., Boughezal, R. et al. Eur. Phys. J. C(2017) 77:829

Mono-jet


Analysis Strategy (ATLAS)

Z(μμ)+jets

W(μν)+jets (b-veto) W(eν)+jets

W(μν)+jets (b-tag)

SR

Simultaneous fit of control and signal regions to extract result

No significant excess above SM backgrounds observed

JHEP 01 (2018) 126



Analysis Strategy (CMS)

SRZ(μμ)+jets

W(eν)+jetsW(μν)+jets

Z(ee)+jets

γ+jets

CM

S-E

XO

-16-

0 48


● Axial-vector and vector models are excluded for mediator massesup to 1.55 TeV to 1.8 TeV for very low DM masses

DM Interpretations

JHEP 01 (2018) 126

CMS-EXO-16-048

Axial-vector Mediator Vector Mediator



DM Interpretations

Scalar colored mediator

● Jet either from ISR or frommediator decay

● Mediator has spin 0, couples tofirst two generations of quarks

● 3 free parameters: mη, m

χ, g

● Minimal mediator width Mediator masses excluded up to1.7 TeV for very low DM masses

JHEP 01 (2018) 126



Searches for DM with Higgs bosons

● Higgs may mix with new dark mediators● H → bb is ~ 58% of BR(H→all), large backgrounds● H → ττ is ~ 6% of BR(H→all), lower background● H → γγ is ~ 0.2% of BR(H→all), very clean final state

Z'-2HDM model

● Baryonic Z' models excluded up to 815 GeVfor m

χ=1 GeV

● MZ' excluded up to 2.6 TeV and m

A up to 0.6

for Z'-2HDM models

Z'B model

Phys. Rev. Lett. 119 (2017) 181804

CMS-PAS-EXO-16-055

NEW

For more details see alsothe talk by D. Moran

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.119.181804


Combination of Searches

DM parameter space is being probed ever more thoroughly

Dijet searches can exclude mediator masses between 50 GeV and2.7 TeV for almost whole DM mass range


Comparison with direct detection experiments

Spin-independent DM-nucleon cross-section

Spin-dependent DM-proton cross-section

● Collider searches complements DD experiments for DM massesbelow 5 GeV for spin-independent DM-nucleon cross-section

● Strong limits for spin-dependent DM-proton cross-section, increasedsensitivity by 3 orders of magnitude


Summary

● DM searches at the LHC remain a thriving field of research

● A large number of mono-X searches have been performedby ATLAS and CMS, already probing a large part of theparameter space– Mono-jet is one of the most powerful channels

● So far no evidence for physics beyond the SM has beenfound

● LHC searches complementary to direct searches

● LHC will provide plenty of new data in the coming years– Stay tuned!


Back-Up


Large Hadron Collider

The LHC

Lake of GenevaInstalled in 26.7 km LEP tunnelDepth of 70 – 140 m

ATLAS

CMS

CMS

● ATLAS and CMS ● General-purpose detectors, covering ~ full solid angle ● Excellent tracking, calorimetry, muon spectrometer


DM Interpretations

● Pseudoscalar models are excluded for mediator masses up to 400GeV and DM masses up to 150 GeV

Pseudoscalar MediatorScalar Mediator

CMS-EXO-16-048 CMS-EXO-16-048


Searches for DM with jets

● Hadronic W/Z decays more common● BR(W → qq) ≈ 3 × BR(W → lν) ● BR(Z → qq) ≈ 10 × BR(Z → ll)

● Makes use of jet substructure ● Primary background: V+jets

● Z (→ νν) + jet, jet fakes W/Z decay Phys. Lett. B 763 (2016) 251

http://www.sciencedirect.com/science/article/pii/S037026931630613X


● Very clean compared to ET

miss+jet ● However, much smaller cross-section

● Signature: large missing transverse energy recoiling against high energetic photon

● Main backgrounds: Z+γ and W+γ

● Vector and axial-vectormodels are excluded up to1.2 TeV for low DM masses

Searches for DM with photons

Eur. Phys. J. C 77 (2017) 393

https://link.springer.com/article/10.1140/epjc/s10052-017-4965-8


Searches for DM with leptonically decaying Z

● An even cleaner final state ● However, further reduced statistics

● Signature: large missing transverseenergy recoiling against two isolatedleptons

● Primary background: VV

● Axial-vector models areexcluded up to 560 GeV forlow DM masses

PLB 776 (2017) 318

CMS-EXO-16-052

http://www.sciencedirect.com/science/article/pii/S0370269317309413


Searches for DM with heavy quarks

● Signature: large missing transverseenergy and boosted heavy quarksdecaying leptonically andhadronically

● Main backgrounds:

– Z+jets, W+jets (low ET

miss)

– tt, Z+jets (high ET

miss)

Eur. Phys. J. C 78 (2018) 18

CMS-EXO-16-051

https://link.springer.com/article/10.1140/epjc/s10052-017-5486-1


Dijet Searches

● DM mediator couples to SM particleand hence can also decay into SMparticles

● Search for new resonances in dijetinvariant mass spectrum

● Standard dijet search: ● Sensitive to m

Z′≥1.5 TeV

● Can we circumvent the triggerbarrier?● Trigger-level search:

● Dedicated data stream allows to godown to 450 GeV

● Dijet+ISR search: ● Trigger on ISR jet or ISR photon ● ISR jet: mediator mass of ≥350 GeV

● ISR γ: mediator mass of ≥200 GeV

Phys. Rev. D 96 (2017) 052004

https://journals.aps.org/prd/abstract/10.1103/PhysRevD.96.052004


Dijet Searches

● Different dijet searches sensitive to different mass regimes● Analyses are working together to probe dark mediator

parameter space ● Combination assumes a lepto-phobic axial-vector mediator

JHEP 01 (2018) 097

http://dx.doi.org/10.1007/JHEP01(2018)097


Combination of Searches

Big picture changes with the choice of couplings

● Dijet and mono-X constraints weakened if gq=0.25 → 0.1

● Strong constraints from dilepton search if gl>0

Searches for dark matter at CMS and...

Documents

Transcript of Searches for dark matter at CMS and...