Search for Dark Matter at the LHC

Transcription

1 Search for Dark Matter at the LHC Steven Lowette Vrije Universiteit Brussel - IIHE 19 November rd CosPa Meeting Université de Liège

2 Content Introduction Generic DM searches at the LHC Explicit DM searches at the LHC Towards LHC Run II Conclusions Page 2

3 Introduction Dark Matter: evidence for BSM physics known to us for over 80 years through gravitational effects now lots of evidence from very diverse scales and effects still we know very little else particle, electrically neutral, not short-lived, not baryonic, not hot as a result, the theoretical landscape is huge three complementary search strategies direct detection indirect detection production at colliders Page 3

4 Introduction Production at colliders DM produced in cascade decays from heavier new states Example: SUSY DM produced directly LSP stable if R-parity conserved always 2 LSP's yielding observable momentum imbalance (MET) Pair production featured in most scenarios but back-to-back DM particles are invisible Higher-order diagrams provide probe recoiling against DM pair Example: Higgs portal SM scalar coupling to dark sector still large invisible Higgs decay width allowed kinematic limit from Higgs mass Page 4

5 Introduction Direct DM production at the LHC experimental approach (mostly) agnostic to production details to proof dark matter was produceds, we must exploit a recoil against some visible SM particle Page 5

6 Introduction Direct DM at the LHC: striking signatures photon pt = 384 GeV MET = 407 GeV CMS-PAS-EXO CMS-PAS-EXO Page 6

7 Introduction Modelling DM production focus on description of direct DM production only effective theories: collapse SM-DM interaction in effective 4-point operator different operator depending on mediator's couplings only few parameters: mdm, EFT scale easy to translate to elastic DM-nucleon cross section limitation: M has to be much larger than the energy scale of the collision probes one interaction at a time simplified models: only SM + DM sector mediator and interactions specified explicitly more parameter space to scan more and more effort in this direction Page 7

8 Generic DM Searches Mono-jet search Submitted to EPJC CMS-PAS-EXO large MET from DM recoils against a jet from QCD ISR selection highlights MET trigger defines lowest analysis cut: MET > 250 GeV one central jet pt > 110 GeV 2nd softer jet allowed close to 1st one control fake jets / instrumental MET electron, muon and tau vetoes suppresses W ℓν irreducible Z νν dominant background after selection Z νν and W ℓν backgrounds predicted from Z μμ and W μν control samples Page 8

9 Generic DM Searches Mono-photon search Submitted to PLB CMS-PAS-EXO large MET from DM recoils against a photon from QED ISR selection highlights photon and photon+met trigger defines lowest analysis cuts: ptγ > 145 GeV and MET > 140 GeV, and Δφ(γ, MET) > 2 photon ID cuts to reject fakes vetos on electron, muon and hadronic activity irreducible Z( νν)γ dominant background after selection other background with genuine photon: W( ℓν)γ fake-photon backgrounds: W eν, QCD, beam halo Page 9

10 Generic DM Searches Mono-lepton search Submitted to Phys.Rev.D CMS-PAS-EXO DM pair produced along with a recoiling W boson selection highlights muon / electron trigger drives analysis cuts pt (e / μ) > 100 / 45 GeV 0.4 < pte/μ / MET < 1.5 Δφ(e/μ, MET) > 0.8 π irreducible W( ℓν) dominant background after selection Page 10

11 Generic DM Searches Di-top + MET search EFT scalar interaction least constrained: quark mass dependence top coupling enhanced selection highlights single-lepton (also dilepton result) 1 electrons/muons, 3 jets, 1 b-tag MET > 320, mtw > 160, mt2w > 200 GeV PA Prel S- imi B2 na G - ry cuts on azimuthal separation leading 2 jets and MET σ > 45 (20) fb excluded at 90% CL for mdm = 50 (1000) GeV Page 11

12 Generic DM Searches Interpretation of mono-jet/photon/lepton & tt+met data compatible with background expectations 90% CL limits set on EFT scale Λ using effective operators from there set limits on elastic DM-nucleon cross section versus DM mass complementary, unique, coverage at low mass and strong sensitivity for spin-dependent interactions Page 12

13 Generic DM Searches strong dependence on interference for monolepton negative interference for ξ=+1 is the most pessimistic scenario Page 13

14 Generic DM Searches also looked at simplified model in monojet analysis here assuming vector mediator production cross section enhancement when mediator can be on-shell EFT limit recovered for large mediator mass Page 14

15 Explicit DM Searches Mono-top search Submitted to PRL CMS-PAS-B2G DM produced through mediator coupling to heavy quarks through FC diagrams selection highlights MET > 350 GeV 3 jets, of which 1 b-tagged electron and muon veto background from ttbar and Z+jets scalar / vector DM 95% CL for masses below 327 / 655 GeV Page 15

16 Explicit DM Searches Higgs portal DM translate Higgs invisible decay width limit into DM constraint VBF analysis [also Z( ℓℓ/bb)H] Eur. Phys. J. C 74 (2014) 2980 VBF trigger 2 jets 50 GeV far in η, close in φ, Mjj > 1100GeV central jet veto lepton veto background from Z( vv)+jets and W( ℓv)+jets BRinv < 0.58 (0.44) at 95%CL [for SM mh = 125GeV] Page 16

17 Explicit DM Searches Higgs portal DM: tth, H inv arx iv: recast of ttbar+met signature from CMS single-lepton stop search 11 into limit on H inv reaching down to BF(H inv) < 0.40 expected < 0.65 authors profited from a low fluctuation in the data Page 17

18 Explicit DM Searches Don't forget SUSY many RPC SUSY searches at the LHC are searches for dark matter produced in cascade decays of higher-mass particles approach SUSY as a DM model example: jets + missing energy is a very generic signature of a coloured particle decaying to a DM candidate many simplified model results available to interpret in more complete models Page 18

19 ATLAS DM Searches ATLAS has similar DM search program additional hadronic mono-w/z additional mono-z interpretation from Z ll PRD 90 (2014) additional b+met, bb+met PRL 112 (2014) arxiv: , submitted to EPJC more examples of use of simplified models most recently in arxiv: , submitted to PRD Page 19

20 Towards the Future DM in LHC upgrades ATLAS has a quite extensive study in ATL-PHYS-PUB including simplified model results CMS monojet reinterpretation in simplified models also studied high-luminosity prospects in arxiv: these are projections, not analysis reoptimizations Page 20

21 Towards the Future 2015 priorities: LHC run at 13 TeV trigger development currently high activity area keep the thresholds as low as possible in the presence of in-time (high lumi) and out-of-time (25ns bunch crossings) event overlap, called pileup provide coherent interpretations in simplified models identify missing signatures / kinematics currently missing in the analyses appropriate comparisons with direct-detection results active exploration by pheno community add external bounds/constraints: eg. dijets, relic density,... improve analyses improve background predictions more advanced signal hypothesis testing beat down systematics add analyses Page 21

22 Search for DM at the LHC Conclusions despite abundant evidence, dark matter is still a mistery large theoretical focus full models, simplified models, effective operator description hep-ph has new articles on dark matter almost daily huge progress in last 5-10 years in dark-matter searches searches for direct and cascade DM production at colliders direct: limits on scale in EFT approach; first limits in simplified model considered next years will be very exciting at LHC new LHC run opening new kinematic phase space from 2015 onwards further exploration of the analysis landscape coherent simplified model interpretations Page 22