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Going after the Dark at Colliders David Berge (CERN)

Going after the Dark at Colliders David Berge (CERN). Going after the Dark at Colliders David Berge (CERN). Setting the stage LEP neutralino constraints LHC neutralino searches LHC contact limits. Particle c: CDM or WDM Axions , gravitinos , or WIMPs.

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Going after the Dark at Colliders David Berge (CERN)

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  1. Going after the Dark at CollidersDavid Berge (CERN)

  2. Going after the Dark at CollidersDavid Berge (CERN) • Setting the stage • LEP neutralino constraints • LHC neutralinosearches • LHC contact limits

  3. Particle c: CDM or WDM Axions, gravitinos, or WIMPs Going after the Dark at CollidersDavid Berge (CERN) Galaxy cluster Abell 2744

  4. Going after the Dark at CollidersDavid Berge (CERN) Galaxy cluster Abell 2744 Particle Dark Matter Searches based on: c SM c c SM c c SM SM SM SM c Direct Indirect Colliders

  5. Going after the Dark at CollidersDavid Berge (CERN) The endpoint of particle Dark Matter searches is a (likely combined) measurement of particle properties which allow connecting back to gravitational measurements! Galaxy cluster Abell 2744 Particle Dark Matter Searches based on: c SM c c SM c c SM SM SM SM c Direct Indirect Colliders

  6. Going after the Dark at CollidersDavid Berge (CERN) Since up to now there are no undisputed positive measurements (definitely true for colliders), interpreting exclusion limits in terms of c involve assumptions about the red bubble! Galaxy cluster Abell 2744 Particle Dark Matter Searches based on: c SM c c SM c c SM SM SM SM c Direct Indirect Colliders

  7. Beyond the Standard Model of Particle Physics Standard Model Extra Dimensions • Large, warped, or universal extra dimensions (…) • Dark Matter • Hierarchy problem: lower Planck mass • Unification of forces Strong elw. symmetry breaking • Modern variants of Technicolor • Dark Matter • Hierarchy problem • Some of the predictions: composite Higgs, new heavy vector bosons, 4th generation of quarks Supersymmetry • Expect spectrum of (not too) heavy superpartners, light neutral Higgs • Dark Matter • Higgs mass stable / hierarchy problem • Unification of gauge couplings • Unification of forces

  8. WIMPs from Supersymmetry As early as 1983 Supersymmetrie’sneutralino identified as WIMP candidate (Goldberg / Ellis et al) • Minimal Supersymmetric Standard Model (MSSM): 105+1+18 parameters • Simplified MSSM sub-spaces with less parameters used as benchmarks • E.g. CMSSM/mSUGRA (5 parameters), NUHM1/2 (5 parameters), pMSSM (19 parameters)… • Neutralinos WIMP candidates: many Supersymmetry versions predict these to be stable, neutral, massive and the lightest particles (Lightest SupersymmetricParticle / LSP)

  9. LEP neutralino constraints

  10. Measure: /g LEP neutralino constraints Use GZ = Ginv + Ghadrons + Gleptons: K. Nakamura et al. (Particle Data Group), Journal of Physics G37, 075021 (2010)

  11. Measure: Ginvcompatible at 2s with 3 light neutrino species, Nn = 2.984 ± 0.008, not much room for: c /g LEP neutralino constraints c Use GZ = Ginv + Ghadrons + Gleptons: • If neutralinos couple to Z boson, LEP’s Ginv implies mc > 46 GeV • Not generically true in MSSM, 0 GeV mc well possible • See e.g. Dreiner et al (Eur.Phys.J.C62:547-572,2009) • Imposing CMSSM constraints, however, mc > 46 GeV holds K. Nakamura et al. (Particle Data Group), Journal of Physics G37, 075021 (2010)

  12. Measure: Ginvcompatible at 2s with 3 light neutrino species, Nn = 2.984 ± 0.008, not much room for: c SM c /g LEP neutralino constraints SM c c Use GZ = Ginv + Ghadrons + Gleptons: • If neutralinos couple to Z boson, LEP’s Ginv implies mc > 46 GeV • Not generically true in MSSM, 0 GeV mc well possible • See e.g. Dreiner et al (Eur.Phys.J.C62:547-572,2009) • Imposing CMSSM constraints, however, mc > 46 GeV holds K. Nakamura et al. (Particle Data Group), Journal of Physics G37, 075021 (2010)

  13. The Large HadronCollider

  14. The Large HadronCollider

  15. The Large HadronCollider

  16. Two General Purpose Experiments: ATLAS & CMS ATLAS CMS

  17. LHC Searches for WIMPs p Q2 = MX X= jets, W, Z, top, Higgs, SUSY, … p Underlying event

  18. Task: measure transverse energy

  19. Difficulty: event pile-up Z+jets: mix of fake and true missing ET Top quark pairs: genuine missing ET from real n’s Z®mm event in ATLAS with 20 reconstructed vertices

  20. 1: “Standard” Dark Matter Searches at Colliders One possibility: search for large missing ET in (supersymmetric) cascade decays jet It’s all about controlling the backgrounds. jet jets/lepton X ETmiss Measure spectra, kinematic endpoints, model fits, etc p p if signal ... + χ01 Number of invisibles Mass scale of invisibles Spin experimental signature:jets + (leptons) + ETmiss [2 LSPs escape scape detection]

  21. 1: “Standard” Dark Matter Searches at Colliders One possibility: search for large missing ET in (supersymmetric) cascade decays SM c jet SM c It’s all about controlling the backgrounds. jet jets/lepton X ETmiss Measure spectra, kinematic endpoints, model fits, etc p p if signal ... + χ01 Number of invisibles Mass scale of invisibles Spin experimental signature:jets + (leptons) + ETmiss [2 LSPs escape scape detection]

  22. 1: “Standard” Dark Matter Searches at Colliders One possibility: search for large missing ET in (supersymmetric) cascade decays squark, gluino SM c mass jet SM c Dm ≈ missing ET! It’s all about controlling the backgrounds. jet jets/lepton LSP / Neutralino X ETmiss Measure spectra, kinematic endpoints, model fits, etc p p Amount of missing ET depends on mass difference! if signal ... + χ01 Number of invisibles Mass scale of invisibles Spin experimental signature:jets + (leptons) + ETmiss [2 LSPs escape scape detection]

  23. ATLAS Supersymmetry Search in Hadronic Final States “At least 7 high-energy jets plus missing transverse energy” ATLAS-CONF-2012-037 Missing transverse energy divided by sqrt of Hadronic transverse energy (“significance of missing ET”). Nothing beyond expected backgrounds, set limits! Limits on CMSSM SUSY models. ATLAS (similarly CMS) excludes under certain model assumptions squarks and gluinos below 850 to 1400 GeV!

  24. CMS Supersymmetry Search in Hadronic Final States CMS-PAS-SUS-12-005 CMS ‘razor’ analysis Searches for pair production of heavy new particles, decaying to LSP and jet(s) Exclusion of squarks and gluinos below 1.3 TeV for equal masses

  25. LHC Impact on constrained Supersymmetry Models CMSSM under a lot of pressure, but other models (with more parameters) remain viable Fit including LHC2011, WMAP, g-2, excluding XENON100 CMSSM scans, points after current LHC SUSY & Higgs results Baer et al 2012, arXiv:1202.4038 arXiv:1112.4192

  26. LHC Impact on constrained Supersymmetry Models CMSSM under a lot of pressure, but other models (with more parameters) remain viable Fit including LHC2011, WMAP, g-2, excluding XENON100 CMSSM scans, points after current LHC SUSY & Higgs results LEP2 Baer et al 2012, arXiv:1202.4038 arXiv:1112.4192 Few-parameter SUSY models like CMSSM increasingly unlikely!

  27. So what? How could strong SUSY production exist but be hidden? ATLAS-CONF-2012-003 Recall: we need to cancel the Higgs virtual corrections. Most important is top loop Contrary to the SM, 3rd generation squarks can be lighter than 1st and 2nd generations Maybe all squarks except stop and sbottom are heavy? Gluinos produce sbottoms which decay to bottom and neutralino. The bottom quarks can be “tagged” in the detector Both ATLAS & CMS focus now heavily on stop/sbottom searches!

  28. So what? ATLAS-CONF-2012-037 How could strong SUSY production exist but be hidden? Maybe the neutralinos are almost as heavy as the squarks and gluinos so that not enough missing ETis produced in the decays to select SUSY events? squark, gluino mass Dm ≈ missing ET! Multi-jet search, this time considering models with gluinos and neutralinos. LSP

  29. So what? ATLAS-CONF-2012-037 How could strong SUSY production exist but be hidden? Maybe the neutralinos are almost as heavy as the squarks and gluinos so that not enough missing ETis produced in the decays to select SUSY events? Maybe squarks and gluinos are all too heavy and only neutralinos (WIMPs) are produced? squark, gluino mass Dm ≈ missing ET! Multi-jet search, this time considering models with gluinos and neutralinos. LSP monojets!

  30. Setting the stage • LEP neutralino constraints • LHC neutralinosearches • LHC contact limits Jet Missing energy ATLAS mono-jet event display

  31. 2: Generic WIMP Searches at Colliders • Consider WIMP pair production at colliders, idea goes back to: • Birkedal et al (hep-ph/0403004) • Beltran et al: Maverick Dark Matter (hep-ph/1002.4137) • Latest papers based on LHC results: • Fox et al, arxiv:1109.4398 and arXiv:1202.1662 (FNAL crew) • Rajamaran et al, arxiv:1108.1196 (UCI crew) • New CMS result in Sarah’s talk after me • Assume WIMPs produced in pairs, expect missing transverse energy plus jet(s)

  32. 2: Generic WIMP Searches at Colliders • Assume: • X exists and can be pair produced • Only X in reach at LHC

  33. 2: Generic WIMP Searches at Colliders • Assume: • X exists and can be pair produced • Only X in reach at LHC

  34. 2: Generic WIMP Searches at Colliders • Assume: • X exists and can be pair produced • Only X in reach at LHC

  35. 2: Generic WIMP Searches at Colliders • Assume: • X exists and can be pair produced • Only X in reach at LHC • Effective field theory approach • X—SM coupling set by mc and L LHC limit on cutoff scale can be translated to direct or indirect detection plane! Cutoff scale

  36. Spin independent Nucleon-WIMP scattering cross section arXiv:1109.4398 LHC measurement translates into one line per operator Low-mass LHC reach complementary to direct-detection experiments LHC limits don’t suffer from astrophysical uncertainties

  37. Spin independent Nucleon-WIMP scattering cross section g g arXiv:1109.4398 LHC measurement translates into one line per operator Low-mass LHC reach complementary to direct-detection experiments LHC limits don’t suffer from astrophysical uncertainties

  38. Spin dependent Nucleon-WIMP scattering cross section arXiv:1109.4398 LHC measurement translates into one line per operator Low-mass LHC reach complementary to direct-detection experiments LHC limits don’t suffer from astrophysical uncertainties

  39. LHC limits on annihilation cross section • DM annihilation at freeze-out temperatures • Assume DM couples to quarks only (else bounds weaker) • Assume effective field theory approach is viable • Masses < 15 and 70 GeVruled out for vector and axial-vector operators arXiv:1109.4398

  40. Summary • Particle Dark Matter searches at colliders integral part of LHC physics • Models / assumptions needed to port collider exclusions to Dark Matter limits • LHC limits potentially very competitive • Hopefully soon we’ll have positive measurements to debate about…

  41. Fermi / HESS limits Fermi stacked Galactic satellites, PRL 107, 241302 (2011) HESS Galactic Center Analysis, PRL 106, 161301 (2011) WIMP annihilation into quark-antiquark pairs

  42. Expected signal missing ET distributions Truth-level, private plot • Take vector operator as example AlpgenZnn+jets PythiaZnn+jets MET ( GeV ) Expect harder MET spectrum even for mc= 0 GeV!

  43. Limits on suppression scale L arXiv:1109.4398 Take vector operator as example Convert cross section limits into limit on L for particular mc

  44. Limits on suppression scale L Compare to values of L consistent with thermal relic density LHC predictions (14 TeV, 100 fb-1) Thermal relic density ATLAS 1 fb-1 measurement (arXiv:1109.4398) L ( GeV ) Increasing relic density Increasing coupling to quarks Tevatron Goodman et al, arXiv:1008.1783 This range excluded under the given assumptions

  45. Limits in “direct-detection plane” • Now convert the high-energy limit on L into limits on sc-Nucleon • Caveats: • Uncertaintyof hadronic matrix elements • Spin-independent vs spin-dependent interactions depending on operator • Simple transfer of LHC limits potentially problematic if • mediators are light • interactions are non-flavour-universal

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