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The Quest for SUSY : issues for collider physics and cosmology

The Quest for SUSY : issues for collider physics and cosmology. S. Kraml (CERN) 1-3 Dec 2006. Supersymmetry (SUSY) is the leading candidate for physics beyond the Standard Model (SM). Symmetry between fermions and bosons Q a |fermion> = |boson>.

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The Quest for SUSY : issues for collider physics and cosmology

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  1. The Quest for SUSY:issues for collider physics and cosmology S. Kraml (CERN) 1-3 Dec 2006

  2. Supersymmetry (SUSY) is the leading candidate for physics beyond the Standard Model (SM). Symmetry between fermions and bosons Qa|fermion> = |boson> This combines the relativistic “external” symmetries (such as Lorentz invariance) with the “internal” symmetries such as weak isospin. unique extension of relativistic symmetries of space-time!

  3. recall Arkani-Hamed‘s comments on the unification of space and time...

  4. ________________________________________________________ The motivations for TeV-scale SUSY include • the solution of the gauge hierachy problem • the cancellation of quadratic divergences • gauge coupling unification • a viable dark matter candidate ________________________________________________________ ... predicts a partner particle for every SM state

  5. The search for SUSY is hence one of the primary objectives of the CERN Large Hadron Colider and a future int. e+e_ linear collider!

  6. This talk • SM problems and SUSY cures • Naturalness and hierachy problems • Gauge coupling unification • The minimal supersymmetric standard model • Particle spectrum • Collider searches: LHC, ILC • The cosmology connection • Dark matter • EW phase transition and baryon asymmetry

  7. SM problems and SUSY cures

  8. The hierachy and naturalness problems • To break the electroweak symmetry and give masses to the SM particles, some scalar field must acquire a non-zero VEV. • In the SM, this field is elementary, leading to an elementary scalar `Higgs' boson of mass mH. However, where L is the scale (=cut-off) up to which the theory is valid.

  9. These large corrections to the SM Higgs boson mass, which should be mH=O(mW), raise problems at two levels: • to arrange for mH to be many orders smaller than other fundamental mass scales, such as the GUT or the Planck scale ―the hierarchy problem, • to avoid corrections dmH2 which are much larger than mH2 itself ― the naturalness problem.

  10. The supersymmetric solution XXX XXX

  11. A light Higgs XXXX XXXX XXXX c.f. talk by W. Hollik

  12. c2 fit of the Higgs boson mass from EW precision data as of Summer 2006

  13. Radiative electroweak symmetry breaking Heavy top effect, drives mH2 < 0 EW scale GUT scale

  14. Grand unification . • GUTs attempt to embed the SM gauge group SU(3)xSU(2)xU(1) into a larger simple group G with only one single gauge coupling constant g. • Moreover, the matter particles (quarks leptons) should be combined into common multiplet representations of G. • Prediction: Unification of the strong, weak and electro-magnetic interactions into one single force g at MX. NB: If MX is too low → problems with proton decay

  15. 1-loop renormalization group evolution of gauge couplings: • SM: • MSSM:

  16. One can also re-write this as

  17. XX Can also be turned into a prediction of the weak mixing angle .....

  18. The MSSM

  19. 1 superpartner for each d.o.f.: qL,R and lL,R L-R mixing ~Yukawas ~ ~ Minimal supersymmetric model MSSM = minimal supersymmetric standard model gauginos + higgsinos mix to 2 charginos + 4 neutralinos Lightest neutralino = LSP 2 Higgs doublets → 5 physical Higgs bosons: neutral states: scalar h, H; pseudoscalar A charged states: H+, H-

  20. XXXX

  21. gluinos, squarks charginos, neutralinos, sleptons Minimal supergravity (mSUGRA) Universal boundary conditions @ GUT scale Heavy top effect, drives mH2 < 0 univ. gaugino mass univ. scalar mass

  22. Recall: Light Higgs XXXX XXXX XXXX c.f. talk by W. Hollik

  23. R parity: symmetry under which SM particles are even _ and SUSY particles are odd If R parity is conserved • SUSY particles can only be produced in pairs • Sparticles always decay to an odd number of sparticles • the lightest SUSY particle (LSP) is stable • any SUSY decay chain ends in the LSP, which is a dark matter candidate

  24. The scale of SUSY breaking

  25. Goldstino and Gravitino

  26. Gravitino mass

  27. SUSY @ colliders

  28. Large Hadron Collider • New accelerator currently built at CERN, scheduled to go in operation in 2007 • pp collisions at 14 TeV • Searches for Higgs and new physics beyond the Standard Model • „discovery machine“, • typ. precisions O(few%)

  29. SUSY searches at LHC

  30. Events for 10 fb-1 background signal Events for 10 fb-1  Tevatron reach ATLAS ET(j1) > 80 GeV ETmiss > 80 GeV signal background Spectacular and large signal From Meff peak first/fast measurement of SUSY mass scale to  20%(10 fb-1, mSUGRA) Caution: also other BSM models lead to missing energy signature → need spin determination

  31. Compare with Higgs search c.f. talk by G. Dissertori

  32. Mass measurements: cascade decays Mass reconstruction through kinematic endpoints [Allanach et al., hep-ph/0007009] Typical precisions: (a) few % [ATLAS, G. Polesello]

  33. International Linear Collider • e+e- collisions at 0.5-1 TeV • Tunable beam energy and polarization • Clean experimental env. • Precision measurements of O(0.1%), c.f. LEP • Global initiative, next big accelerator after LHC?

  34. ILC: Precision measurements with tunable beam energy and polarization [TESLA TDR] can reach O(0.1%) precision see talk by H.-U. Martyn

  35. High-scale parameter determination c.f. talk by W. Porod

  36. The cosmology connection Higgs? SUSY? • dark matter • dark energy • baryon asymmetry • inflation • .... 1 GeV ~ 1.3 * 1013 K

  37. What is the Universe made of? • Cosmological data: • 4% ±0.4% baryonic matter • 23% ±4% dark matter • 73% ±4% dark energy • Particle physics: • SM is incomplete; expect new physics at the TeV scale • Hope that this new physics also provides the dark matter • Discovery at LHC, precision measurements at ILC ?

  38. WIMPs (weakly interacting massive particles) • DM should be stable, electrically neutral, weakly and gravitationally interacting • WIMPs are predicted by most theories beyond the Standard Model (BSM) • Stable as result of discrete symmetries • Thermal relic of the Big Bang • Testable at colliders! Neutralino, gravitino, axion, axino, LKP, T-odd Little Higgs, branons, etc., ... BSM dark matter

  39. Relic density of WIMPs (weakly interacting massive particles) • Early Universe dense and hot; WIMPs in thermal equilibrium • Universe expands and cools;WIMP density is reduced through pair annihilation; Boltzmann suppression: n~e-m/T • Temperature and densitytoo low for WIMP annihilation to keep up with expansion rate → freeze out Final dark matter density: Wh2 ~ 1/<sv> Thermally avaraged cross section of all annihilation channels

  40. Neutralino LSP as dark matter candidate

  41. Neutralino system Gaugino m´s Higgsino mass Neutralino mass eigenstates → LSP

  42. Neutralino relic density c0 LSP as thermal relic: relic density computed as thermally avaraged cross section of all annihilation channels → Wh2 ~ 1/<sv> Wh2 = 0.1 with 10% acc. puts strong bounds on the parameter space

  43. Annihilation into gauge bosons • cc→ WW / ZZ mainly through t-channel chargino / neutralino exchange; typically also some annihilation into Zh, hh • Does not occur for pure bino; LSP needs to be mixed bino-higgsino(or bino-wino) • Pure wino or higgsino LSP: • neutral and charged states are a mass-degenerate triplet, • (co)annihilation too efficient • Right relic density for • (|m|-M1)/M1 ~ 0.3, • (M2-M1)/M1 ~ 0.1 [hep-ph/0604150]

  44. Coannihilations • Occur for small mass differences between LSP and next-to-lightest sparticle(s); efficient channel for a bino-like LSP • Typical case: coann. with staus • Key parameter is the mass difference DM = mNLSP−mLSP • Other possibilities: Coannihilation with stops (DM~20-30GeV), coann. with chargino and the 2nd neutralino (in non-unified models)

  45. mSUGRA parameter space • GUT-scale boundary conditions: m0, m1/2, A0 [plus tanb, sgn(m)] • 4 regions with right Wh2 • bulk (excl. by mh from LEP) • co-annihilation • Higgs funnel (tanb ~ 50) • focus point (higgsino scenario)

  46. Prediction of Wh2 from colliders: Requires precise measurements of • LSP mass and decomposition bino, wino, higgsino admixture • Sfermion masses (bulk, coannhilation) or at least lower limits on them • Higgs masses and widths: h,H,A • tanb Required precisions investigated in, e.g. Allanach et al, hep-ph/0410091 and Baltz et al., hep-ph/0602187 c.f. talks by H.U. Martyn & B. Allanach NB: determination of <sv> also gives a prediction of the (in)direct detection rates

  47. For a precise prediction of Wh2 we need precision measurements of most of the SUSY spectrum (masses and couplings) → LHC+ILC ← LHC WMAP ILC

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