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Dark Matter @ The LHC

Dark Matter @ The LHC. Yi Cai KITPC, Beijing June 20, 2012 June 2012. Disclaimer. Unspoken rules(潜规则): your own work Unfortunately none is presented here. Please don’t mobilize the masses to ban me!(请勿发动群众封杀我！). Why do we care?. Astrophysical evidences Rotation curve Bullet cluster

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Dark Matter @ The LHC

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  1. Dark Matter @ The LHC • Yi Cai • KITPC, Beijing • June 20, 2012 • June 2012

  2. Disclaimer • Unspoken rules(潜规则): your own work • Unfortunately none is presented here. • Please don’t mobilize the masses to ban me!(请勿发动群众封杀我！)

  3. Why do we care? • Astrophysical evidences • Rotation curve • Bullet cluster • Cosmic microwave background • Energy budget

  4. What could it be? • Modify gravity itself? • MACHOs? • Hot dark matter? • Cold or warm dark matter? • Axions • Gravitinos • WIMPs

  5. What can we do? • Theory: maybe already more than enough on the market • Experiment • Direct detection • Indirect detection • Collider experiments

  6. Comparison • Direct • Local DM densities • Velocity distribution • Less sensitive to spin • Indirect • Profile of DM halo • Cosmic ray propagation • Collider • Light DM • Spin dependent

  7. LHC Basics • Location:the Swiss and French border • Depth: 50-175 m • Circumference: 27km • Beam energy: 7? TeV

  8. What can we see? • Standard signals • Missing transverse energy • Jets • Leptons • Photons • New physics: a needle buried deep in a haystack • Challenge: control the background

  9. Model Dependent Approach • The most studied theories • Supersymmetry • Extra dimensions • Little Higgs • ...... • Signature: new stuff+MET

  10. DM candidate SUSY Basics • Particle number: doubled • Parameters > 100 in the MSSM • Various SUSY breaking mechanisms • mSUGRA • AMSB • GMSB • Split SUSY

  11. mSUGRA • 5 parameters: m0, m1/2, tanbeta, A0,sign(mu) • Different regions • Bulk region • Focus point • Co-annihilation region • Rapid annihilation funnel

  12. Bulk Region • Annihilation via slepton exchange • Solve from endpoints in dilepton mass and dilepton+jet mass, min value of dilepton+jet mass and max value of single lepton+jet mass

  13. Pros and Cons • very sensitive • pheno changes drastically with modifications • Only DM candidates found

  14. Model independent • Assumption • Fermionic dark matter & heavy mediator • Effective operators with a universal cutoff • Two parameters: DM mass and the cutoff

  15. Monophoton @ CMS • Pair production • Requirements: • Photon: Pt > 145 GeV • In the central region |η|<1.442 • Shower shape consistent with photon • MET > 130 GeV • Remove events • jet with Pt > 40 GeV and |η| < 3 • nearby tracks or pixel stubs • significant hadronic activity • significant electromagnetic calorimeter activity • Aggressive isolation-based clean-up.

  16. Major Background • Bkg from pp collision • pp-> Zγ->ννγ irreducible • pp->W->eγ e misidentified as photon • pp->jets->”γ”+MET j mimics γ, MET from j mis-measurement • pp->γ+jet MET from j mis-measurement • pp->Wγ->lνγ l escapes • pp->γγ γ mis-measured • Bkg also comes from cosmics, neutron and beam halo

  17. Limits • CLs limits calculated for an integrated luminosity of 4.67 fb^- • Assumption:cross section scales as Λ^4 SI SD

  18. Combined with Direct Detection

  19. Monojet • Event selection • MET>200 GeV (>350 for DM search) • # of jets 1 or2 • pT(1) >110 GeV, |η|<2.4 • pT(2)>30 GeV • Δφ(1,2)<2.5 • Rejection • isolated e, μ and tracks

  20. Events • Data-driven estimation of Z+jets and W+jets • Final numbers for MET>350 GeV, 1124±101 bkg, 1142 data

  21. Monojet and Monophoton

  22. Then? • Other operators? • Mediator not so heavy? One more parameter. • A special case: Higgs portal • With indirect search? • More!!

  23. Summary • DM is an important topic beyond the Standard Model. • Various DM searching strategies have their own pros. and cons. • LHC can in principle produce DM, place stringent constraints or even find good DM candidates. • Future LHC data may eventually shed some real light on this puzzle.

  24. References • arXiv:1005.3797, 1005.1286, 1008.1783, 1108.1196, 1109.4398, 1103.0240, 1109.4398 • JHEP 1012:048(2010) • Phys. Rev. D82: 116010(2010)

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