Searches for dark matter at CMS and ATLAS

Transcription

1 Searches for dark matter at CMS and ATLAS K. Bierwagen Johannes Gutenberg University Mainz On behalf of the ATLAS and CMS Collaboration March 20, 2018

2 Introduction Astrophysical observations point to the existence of Dark Matter (DM) Rotation curves Bullet Cluster CMB Underlying nature of DM remains unknown WIMP paradigm Motivation to consider collider searches for DM 2

3 Dark Matter Signatures Mono-photon Mono-jet Mono-W/Z Mono-Higgs Mono-b/bb A wide range of final states can be investigated with the LHC Mono-t/tt For more details on dijet searches see talks by C. Gwilliam and D. Moran 3

4 Missing Transverse Energy 4

5 Search for DM with jets Largest ETmiss+X cross-section at LHC background signal MET Jet pt of 973 GeV balanced by a ETmiss of 954 GeV Search for high MET excess 5

6 Signal Region Jet pt>250 GeV η <2.4 e & μ veto Up to 3 additional jets (pt>30 GeV) CMS-EXO > 0.4 MET > 250 GeV N.B. ATLAS selection for illustration purpose JHEP 01 (2018) 126 Crucial to measure SM background precisely 6

7 Backgrounds Mono-jet Low MET Main Backgrounds Z(vv)+jets: irreducible W(lv)+jets: irreducible when leptons are out of detector acceptance Backgrounds constrained in dedicated control regions V+jet modeled at NNLO QCD & NLO EW Includes theory predictions via MC reweighting based on pt(v) ATLAS CMS High MET Other 6% W+jets Z+jets 38% 57% Other 5%W+jets 23% Z+jets 72% Other 4% W+jets Z+jets 37% 59% Other 6%W+jets 11% Z+jets 84% Lindert, J.M., Pozzorini, S., Boughezal, R. et al. Eur. Phys. J. C(2017) 77:829 7

8 Analysis Strategy (ATLAS) Simultaneous fit of control and signal regions to extract result W(μν)+jets (b-veto) W(eν)+jets JHEP 01 (2018) 126 SR W(μν)+jets (b-tag) Z(μμ)+jets No significant excess above SM backgrounds observed 8

9 Analysis Strategy (CMS) Z(ee)+jets SR CMS-EXO Z(μμ)+jets W(μν)+jets γ+jets W(eν)+jets 9

10 DM Interpretations Axial-vector Mediator Vector Mediator CMS-EXO JHEP 01 (2018) 126 Axial-vector and vector models are excluded for mediator masses up to 1.55 TeV to 1.8 TeV for very low DM masses 10

11 DM Interpretations Scalar colored mediator JHEP 01 (2018) 126 Jet either from ISR or from mediator decay Mediator has spin 0, couples to first two generations of quarks 3 free parameters: mη, mχ, g Minimal mediator width Mediator masses excluded up to 1.7 TeV for very low DM masses 11

12 Searches for DM with Higgs bosons Higgs may mix with new dark mediators Z'-2HDM model 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 NEW Phys. Rev. Lett. 119 (2017) CMS-PAS-EXO Z'B model Baryonic Z' models excluded up to 815 GeV for mχ=1 GeV MZ' excluded up to 2.6 TeV and ma up to 0.6 For more details see also for Z'-2HDM models the talk by D. Moran 12

13 Combination of Searches DM parameter space is being probed ever more thoroughly Dijet searches can exclude mediator masses between 50 GeV and 2.7 TeV for almost whole DM mass range 13

14 Comparison with direct detection experiments Spin-independent DM-nucleon cross-section Spin-dependent DM-proton cross-section Collider searches complements DD experiments for DM masses below 5 GeV for spin-independent DM-nucleon cross-section Strong limits for spin-dependent DM-proton cross-section, increased sensitivity by 3 orders of magnitude 14

15 Summary DM searches at the LHC remain a thriving field of research A large number of mono-x searches have been performed by ATLAS and CMS, already probing a large part of the parameter space Mono-jet is one of the most powerful channels So far no evidence for physics beyond the SM has been found LHC searches complementary to direct searches LHC will provide plenty of new data in the coming years Stay tuned! 15

16 Back-Up 16

17 Large Hadron Collider Installed in 26.7 km LEP tunnel Depth of m Lake of Geneva CMS The LHC ATLAS CMS ATLAS and CMS General-purpose detectors, covering ~ full solid angle Excellent tracking, calorimetry, muon spectrometer 17

18 DM Interpretations Scalar Mediator Pseudoscalar Mediator CMS-EXO CMS-EXO Pseudoscalar models are excluded for mediator masses up to 400 GeV and DM masses up to 150 GeV 18

19 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)

20 Searches for DM with photons Very clean compared to ETmiss+jet However, much smaller cross-section Signature: large missing transverse energy recoiling against high energetic photon Main backgrounds: Z+γ and W+γ Eur. Phys. J. C 77 (2017) 393 Vector and axial-vector models are excluded up to 1.2 TeV for low DM masses 20

21 Searches for DM with leptonically decaying Z An even cleaner final state However, further reduced statistics Signature: large missing transverse energy recoiling against two isolated leptons Primary background: VV PLB 776 (2017) 318 CMS-EXO Axial-vector models are excluded up to 560 GeV for low DM masses 21

22 Searches for DM with heavy quarks Signature: large missing transverse energy and boosted heavy quarks decaying leptonically and hadronically Main backgrounds: Z+jets, W+jets (low ETmiss) tt, Z+jets (high ETmiss) Eur. Phys. J. C 78 (2018) 18 CMS-EXO

23 Dijet Searches DM mediator couples to SM particle and hence can also decay into SM particles Search for new resonances in dijet invariant mass spectrum Standard dijet search: Phys. Rev. D 96 (2017) Sensitive to mz 1.5 TeV Can we circumvent the trigger barrier? Trigger-level search: Dedicated data stream allows to go down 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 23

24 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)

25 Combination of Searches Big picture changes with the choice of couplings Dijet and mono-x constraints weakened if gq= Strong constraints from dilepton search if gl>0 25