Dark The LHC Yi Cai KITPC, Beijing June 20, 2012 June 2012

Yi Cai, SJTU 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！ )

Yi Cai, SJTU Why do we care? Astrophysical evidences Rotation curve Bullet cluster Cosmic microwave background Energy budget

Yi Cai, SJTU What could it be? Modify gravity itself? MACHOs? Hot dark matter? Cold or warm dark matter? Axions Gravitinos WIMPs

Yi Cai, SJTU What can we do? Theory: maybe already more than enough on the market Experiment Direct detection Indirect detection Collider experiments

Yi Cai, SJTU Comparison Direct Local DM densities Velocity distribution Less sensitive to spin Indirect Profile of DM halo Cosmic ray propagation Collider Light DM Spin dependent

Yi Cai, SJTU LHC Basics Location:the Swiss and French border Depth: m Circumference: 27km Beam energy: 7? TeV

Yi Cai, SJTU 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

Yi Cai, SJTU Model Dependent Approach The most studied theories Supersymmetry Extra dimensions Little Higgs Signature: new stuff+MET

Yi Cai, SJTU SUSY Basics Particle number: doubled Parameters > 100 in the MSSM Various SUSY breaking mechanisms mSUGRA AMSB GMSB Split SUSY DM candidate

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

Yi Cai, SJTU 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

Yi Cai, SJTU Pros and Cons very sensitive pheno changes drastically with modifications Only DM candidates found

Yi Cai, SJTU Model independent Assumption Fermionic dark matter & heavy mediator Effective operators with a universal cutoff Two parameters: DM mass and the cutoff

Yi Cai, SJTU 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.

Yi Cai, SJTU 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

Yi Cai, SJTU Limits CLs limits calculated for an integrated luminosity of 4.67 fb^- Assumption:cross section scales as Λ^4 SI SD

Yi Cai, SJTU Combined with Direct Detection

Yi Cai, SJTU 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

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

Yi Cai, SJTU Monojet and Monophoton

Yi Cai, SJTU Then? Other operators? Mediator not so heavy? One more parameter. A special case: Higgs portal With indirect search? More!!

Yi Cai, SJTU 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.

Yi Cai, SJTU References arXiv: , , , , , , JHEP 1012:048(2010) Phys. Rev. D82: (2010)