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Searches for di-lepton and di-photon resonances at ATLAS

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  1. Searches for di-lepton anddi-photon resonances at ATLAS Yanwen Liu University of Science and Technology of China (USTC) On behalf of the ATLAS collaboration OCPA7, Yanwen Liu/USTC

  2. Outline • LHC and ATLAS • Searches with photon pairs • Higgs • Gravitons • Searches with lepton pairs • Gravitons • Z’ • R-parity violating sneutrino • Summary OCPA7, Yanwen Liu/USTC

  3. Experiments at LHC +LHCf, TOTEM OCPA7, Yanwen Liu/USTC

  4. Muon spectrometer • air-core toroids, • MDT+RPC+TGC+CSC • s/pT ~ 2-7 % • |h| < 2.7,|h|<2.5 ( precision • phys.) Length: ~ 46 m Radius : ~ 12 m Weight : ~ 7000 tons Channels: ~ 108 Lcable: ~ 3000 km Cost: 541M CHF • EM Calorimetry • Pb-LAr • s/E ~ 10%/√E(GeV)1% • |h|<3.2, |h| < 2.5 (fine granularity) • Inner detector (B=2 T) • Si pixels and strips • Transition Radiation Detector • (e/ separation) • s/pT ~ 0.05% pT(GeV)0.1%; • |h| < 2.5, B=2 T(central solenoid) • Hadron Calorimeter • Fe/scintillator (central), Cu/W-LAr (fwd) • s/E ~ 50%/√E(GeV)3% • ||<3 OCPA7, Yanwen Liu/USTC

  5. Data collection 2011: steadily delivering ! data-taking efficiency ~95% Peak luminosity : 1.75x1033 cm-2s-1 7 TeV 2010: Exponential ramping up of luminosity OCPA7, Yanwen Liu/USTC

  6. Search for Higgs in di-photons arxiv: 1107.0975v1 http://cern.ch/gfitter Low mass Higgs is favored by the global electroweak fitting. γγ is one of the most promising channels at low mass. OCPA7, Yanwen Liu/USTC

  7. Analysis overview • Two photon candidates PT1>40 GeV, PT2>25 GeV, 1.52<|η|<2.37 and |η|<1.37 • Background : γγ(~70%), γj +jj (~28%) and ee(~2%, relevant near Z pole) • Events are divided into 5 non-overlapping categories for different signal/background and resolutions No significant excess mH =120 GeV, expect ~18 events OCPA7, Yanwen Liu/USTC

  8. The ATLAS picture on Higgs • Dominating systematic uncertainties for γγ channel: • signal normalization: photon ID efficiency (11%) • mass resolution : 14% in total. OCPA7, Yanwen Liu/USTC

  9. Randall-Sundrum gravitons A possible “explanation” to the hierarchy problem One extra dimension of finite size(rc), φ : 0 -> π. “Warped” metric: PRL83(1999)3370 K-K excitation of gravitons observable at hadron colliders Two model parameters: k/Mpl, mG OCPA7, Yanwen Liu/USTC

  10. RS limits from 2010 data Excluded at 95%CL Mass > 920 (545) GeV for k/Mpl=0.1(0.02) 2011 data analysis in progress. OCPA7, Yanwen Liu/USTC

  11. Search Di-lepton resonances e+e- μ+μ- Two isolated electrons with ET>25 GeV. |η|<1.37 and 1.52<|η|<2.47 For 1500 GeV Z’, acceptance ~65% Two isolated muonswith PT>25 GeV For 1500 GeV Z’, acceptance ~40% Background estimated using MC simulations. Normalized to data using 70 GeV<M<110 GeV (scaling factor differs from 1 by less than 1%) OCPA7, Yanwen Liu/USTC

  12. Constraints on RS gravitons and Z’ Two benchmark models Sequential Standard Model (SSM) E6 : SU(5)xU(1)xU(1) The two U(1) fields can mix RS gravitons, spin=2 0.7 TeV for k/Mpl= 0.01 1.63 TeV for k/Mpl = 0.1 1.83 TeV SSM OCPA7, Yanwen Liu/USTC

  13. Search for e+μ resonances Example models: Lepton-Flavor-Violating Z’ R-parity violating sneutrino. For 0.7 TeV Z’, σ(pp->Z’+X)*Br(Z’->eμ) < 10.7 fb λ311’, λ312 ≠ 0 All other couplings = 0 OCPA7, Yanwen Liu/USTC

  14. Summary One of the projections presented at EPS 2011. Not validated by LHC Machine Committee. • No discoveries in 1fb-1. • We will have much more data soon Stay tuned! log scale! OCPA7, Yanwen Liu/USTC

  15. THANKS! OCPA7, Yanwen Liu/USTC

  16. BACK-UP Some slides are borrowed from EPS 2011 talks OCPA7, Yanwen Liu/USTC

  17. OCPA7, Yanwen Liu/USTC

  18. ATLAS Higgs-> γγcategories OCPA7, Yanwen Liu/USTC

  19. OCPA7, Yanwen Liu/USTC

  20. CMS Higgs status OCPA7, Yanwen Liu/USTC

  21. Hgg Low sensitivity, high resolution (1-2 GeV today but further improvements possible), tiny signal on a smoothly falling background; challenges: vertexing with PU, calibrations and transparency corrections for the crystals. CMS PAS-HIG-11-010 CMS PAS-HIG-11-011 OCPA7, Yanwen Liu/USTC

  22. CDF Higgs status OCPA7, Yanwen Liu/USTC

  23. OCPA7, Yanwen Liu/USTC

  24. Tevatron Higgs status OCPA7, Yanwen Liu/USTC

  25. Tevatron Combination OCPA7, Yanwen Liu/USTC

  26. Z’/GKK High pT di-leptons CMS-PAS-EXO-11-019. We study in detail the high mass tail of the Z. Since spectra are consistent with known SM processes we extract 95% CL limits. Z’e+e- Z’m+m- Z’e+e- orm+m- 1940 GeV for the Sequential Standard Model Z′SSM, 1620 GeV for Super-String inspired models, Z′ψ. 1450-1780 GeV for RS Kaluza-Klein Gravitonsfor (k/MPl) 0.05-0.1. OCPA7, Yanwen Liu/USTC

  27. LHC 2011 schedule OCPA7, Yanwen Liu/USTC