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Exploring Dark Matter at the LHC: Implications and Strategies for Discovery

This presentation discusses dark matter (DM) exploration through experiments conducted at the Large Hadron Collider (LHC). It covers astrophysical evidence supporting the existence of DM, such as rotation curves and cosmic microwave background data. The talk details various dark matter candidates, including WIMPs, axions, and MACHOs, and elaborates on detection methods like direct and indirect detection, as well as collider experiments. Finally, it outlines the significance of dark matter in understanding physics beyond the Standard Model and the potential of LHC data to unveil new discoveries.

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Exploring Dark Matter at the LHC: Implications and Strategies for Discovery

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Presentation Transcript

  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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