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Supersymmetry at LHC

Supersymmetry at LHC. Hyun Min Lee CERN. Korea CMS-Theory meeting, CERN, January 14, 2011. Why is beyond the Standard Model?. Model Building. Predictions. Observations. Discrepancies of observed data with theoretical predictions call for “new models”.

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Supersymmetry at LHC

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  1. Supersymmetry at LHC Hyun Min Lee CERN Korea CMS-Theory meeting, CERN, January 14, 2011

  2. Why is beyond the Standard Model? Model Building Predictions Observations • Discrepancies of observed data with theoretical predictions call for “new models”. • Solving theoretical problems require “new ideas”, leading to predictions to be observed by experiments.

  3. The SM has been successful in explaining all the known electroweak data. However, the SM is incomplete. • Electroweak symmetry breaking: weak or strong dynamics? • Unification of forces? • Dark matter? • Quantum theory of gravity? • Neutrino masses? • Baryon asymmetry? • Fermion mass hierarchies and mixings? …

  4. The Standard Model • Based on gauge symmetry • 3 copies of quarks and leptons with different masses • Force carriers: gluon, • is broken to

  5. Higgs mechanism in the SM • Spontaneous symmetry breaking: through VEV of an operator that changes under the symmetry. • Higgs mechanism breaks electroweak symmetry by the weakly coupled scalar dynamics: • Higgs mechanism in the SM also gives masses to quarks and leptons. • Higgs mechanism leads to the neutral Higgs boson • Electroweak precision data are compatible with the SM predictions in the presence of the Higgs boson of weak-scale mass.

  6. Higgs mass bound • Weakly coupled until high energies: • Unitarity bound: • Electroweak precision data, direct searches: W W W W W W W H W

  7. Light Higgs and hierarchy problem • Suppose that the light Higgs boson is present as suggested by electroweak data. • If the SM is valid at high energy scales, Neutrino masses: Gauge coupling unification: Planck scale: it is unnatural to maintain the light Higgs boson such that : hierarchy problem.

  8. Solutions to hierarchy problem • Hierarchy problem consists in UV sensitive quantum corrections to the Higgs mass: • Solutions: i) : Strongly coupled dynamics like QCD, e.g. in technicolor, Higgs is composite, ii) Cancellation between various contributions to the Higgs mass: “Supersymmetry”

  9. Supersymmetry • The additional contribution of superpartners cancels the quadratic term in the one-loop Higgs mass by • SUSY is the mathematical extension of translation and Lorentz invariances: [Haag-Lopuszanski-Sohnius] with • SUSY generator is a spinor under Lorentz transformation so its action is the exchange between a fermion and a scalar boson with same masses and charges.

  10. MSSM squarks sleptons Higgsinos photino wino, zino gluino

  11. SUSY couplings • A pair of superparticles in each vertex

  12. R-parity & LSP • Baryon & Lepton number conservation in MSSM is not guaranteed by gauge symmetry only. • Imposing R-parity forbids dangerous B/L violations: • Consequences of R-parity • LSP(Lightestsuperparticle) is stable. If neutral, it becomes Dark matter (e.g. lightest neutralino). • Non-LSP decays into odd # of LSPs, typically one LSP. • Superparticles are produced in pairs.

  13. Spont. SUSY breaking • If SUSY is exact, superparticles would have equal masses to SM partners. • SUSY must be broken in the vacuum: • In order not to have masslessGoldstino, there must be a gauge fermion : supergravity. : super-Higgs mechanism × ×

  14. Goldstino interaction with superpartner pair • Squark contribute to the one-loop Higgs mass, meaning that for the light Higgs. for well-defined limit

  15. Any fermion in the MSSM cannot be a Goldtino. i) SM fermions: observed as independent d.o.f.s ii) Photino: scalar masses , Moreover, wino and zino remain massless. iii) Sum rule: • SUSY breaking must occur in hidden sector, being mediated to the MSSM. • SUSY breaking is parametrized by soft mass parameters,

  16. Gauge coupling unification • SM gauge couplings change in energy scale Q due to screening of charged particles in vacuum, • Weak-scale superpartners contribute to the running of gauge couplings: • cf. SM: • Gauge couplings are unified at • much better than in SM.

  17. Gaugino masses run in energy scales, • Universal gaugino masses at GUT scale lead to • Scalar masses also run. • Equal scalar masses at GUT scale become split. • large top Yukawa coupling drives up-type Higgs mass to negative for electroweak symmetry breaking.

  18. SUSY mediation Initial superpartner masses at GUT scale depend on SUSY mediation mechanisms.

  19. SUSY signals at LHC • 2010-2011 LHC at plans to collect luminosity of • Superparticles produced in pair, each cascade decaying into an LSP. • Undetected LSPs: large missing transverse momentum • Typical final states: LSP + jets + leptons • Needs cuts on pt to reduce QCD multi-jets and SM backgrounds, e.g. neutrinos from W/Z bosons • mSugra limits from Tevatron:

  20. Transverse mass Process: • Invariant mass • Missing transverse momentum • Transverse mass • Invariant under longitudinal boosts (: independent of lab and partonc.m.)

  21. zero-Lepton • zero-lepton 2jet channel : Highest discovery channel • Cuts: Pt(jet)>[70,30]GeV, MET>40GeV SU4 - SUSY benchmark point close to the Tevatron bound m(q,g)~410GeV

  22. 1-lepton • Electron, muon channels • Cuts: Pt(lepton)>20GeV (no further lepton with Pt>10GeV)), Pt(jets)>30GeV (at least two jets), MET>30GeV W,top background suppression

  23. Discovery reach at LHC • 0-lepton and 1-lepton channels most powerful • even with ATLAS and CMS can significantly surpass the Tevatron and LEP limits • With squark and gluino up to 600-700 GeV can be discovered mSUGRA , A0=0, tanβ=10, μ>0 (ATL-PHYS-SLIDE-2010-495)

  24. Update on jets at CMS • New result from CMS at 7TeV with (arXiv: 1101.1628 [hep-ex] ) • jets + missing transverse energy

  25. Agreement between estimated SM background and observed events exclude SUSY events more than 13.4 at 95% C.L. • In turn, constraints on msugra or CMSSM parameter space.

  26. SUSY Higgs boson • There are two Higgs doublets in MSSM: 3 would-be Goldstons: eaten by W/Z bosons 5 Higgs bosons: • give masses to up-type quarks and down-type quarks(charged leptons) by • Upper bound on the neutral light Higgs mass:

  27. Couplings to fermions and gauge bosons go to the SM case in the decoupling limit, (LHC wedge) (95% C.L.)

  28. Conclusion • Supersymmetry is a well-motivated scenario beyond the Standard Model, solving the hierarchy problem. • In mSugra with R-parity conservation, gluino and squark of masses 600-700 GeV could be discovered at LHC with • SUSY mediation can be identified by the nature of LSP. • SUSY prefers the light Higgs boson, which is accessible at LHC. • Other Higgs bosons in the MSSM could be also discovered with integrated luminosity at LHC.

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