1 / 69

The Search For Supersymmetry

The Search For Supersymmetry. Liam Malone and Matthew French. Supersymmetry A Theoretical View. Introduction. Why do we need a new theory? How does Supersymmetry work? Why is Supersymmetry so popular? What evidence has been found?. The Standard Model. 6 Quarks and 6 Leptons.

alban
Download Presentation

The Search For Supersymmetry

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. The Search For Supersymmetry Liam Malone and Matthew French

  2. SupersymmetryA Theoretical View

  3. Introduction • Why do we need a new theory? • How does Supersymmetry work? • Why is Supersymmetry so popular? • What evidence has been found?

  4. The Standard Model • 6 Quarks and 6 Leptons. • Associated Anti-Particles. • 4 Forces – but only successfully describes three.

  5. Symmetries and Group Theory • Each force has an associated symmetry. • This can be described by a group. • The group SU(N) has N2-1 parameters. • These parameters can be seen as the amount of mass-less bosons required to mediate the force. • Ideally the standard model is a SU(3)×SU(2)×U(1) model.

  6. Weak Force • Weak force is very short range due to its massive bosons. • Have difficulty adding massive bosons and keeping the gauge invariance of the theory. • Yet scalar bosons are proposed. • Some other process is taking place.

  7. The Higgs Mechanism • Higgs mechanism solves this problem. • Uses SPONTANEOUS SYMMETRY BREAKING. • Mix the SU(2) and U(1) symmetry into one theory. • Creates three massive bosons for the weak force, the Higgs and the mass-less photon.

  8. Renormalisation • Used to calculate physical quantities like the coupling constants of each force or the mass of a particle. • Sum over all interactions. • Have to use momentum cut-off. • Results in the quantity being dependant on the energy scale it is measured on.

  9. The Hierarchy Problem • Renormalizing fermion masses gives contributions from: • Renormalising the Higgs mass gives contributions from:

  10. Other Problems with the Standard Model • No one knows why the electroweak symmetry is broken at this scale. • Why are the three forces strengths so different? • Why the 21 seemingly arbitrary parameters?

  11. History of Supersymmetry • First developed by two groups, one in USSR and one in USA. • Gol’fund and Likhtmann were investigating space-time symmetries in the USSR. • Pierre Ramond and John Schwarz were trying to add fermions to boson string theory in the USA.

  12. Supersymmetry • In renormalisation fermion terms and boson terms have different signs. • Therefore a fermion with the same charge and mass a boson will have equal and opposite contributions. • The basis of supersymmetry – every particle has a super partner of the opposite type.

  13. Supersymmetry • In Quantum Mechanics this could be written as: • The operator Q changes particle type. • Q has to commute with the Hamiltonian because of the symmetry involved:

  14. Supersymmetry • The renormalised scalar mass now has the contributions from two particles: • The only thing that this requires is the stability of the weak scale:

  15. Constraints on SUSY • 124 parameters required for all SUSY models. • However some phenomenological constraints exist. • These mean some SUSY models are already ruled out.

  16. Minimal Supersymmetric Standard Model • In supersymmetry no restrictions are placed on the amount of new particles. • Normally restrict the amount of particles to least amount required. • This is the Minimal Supersymmetric Standard Model (MSSM).

  17. MSSM • All particles gain one partner. • Gauge bosons have Gauginos: • E.g The Higgs has the Higgsinos. • Fermions have Sfermions: • E.g Electron has Selectron and Up quark has the Sup.

  18. Constrained MSSM • A subset of the MSSM parameter space. • Assumes mass unification at a GUT scale. • This gives only five parameters to consider.

  19. The Five Parameters • M1/2 the mass that the gauginos unify at. • M0 the mass at which the sfermions unify at. • Tan β is the ratio of the vacuum values of the two Higgs bosons. • A0 is the scalar trilinear interaction strength. • The sign of the Higgs doublet mixing parameter.

  20. Figure showing the mass unification at grand scales. The five parameters m1/2=250 GeV, m0 = 100 GeV, tan β= 3, A0=0 and μ>0.

  21. Local or Global? • Supersymmetry could be local or global symmetry. • Local symmetries are like the current standard model. • If SUSY is global has implications on symmetry breaking mechanisms.

  22. SUSY Breaking • SUSY has to be broken between current experiment scales and Planck scale. • Natural to try and add in Higgs mechanism but this reintroduces Hierarchy problem. • Two possible ways: • Gravity • Interactions of the current gauge fields and the superpartners

  23. Gravity mediated breaking • In super gravity get graviton and gravitino. • Gravitino acquires mass when SUSY is broken. • If gravity mediates the breaking, LSP is the neutalino or sneutrino.

  24. Gauge Mediated Breaking • If SM gauge fields mediate the SUSY breaking then SUSY is broken a lower scale. • Gravitino therefore has a very small mass and is the LSP. • Other Models do exist.

  25. R-Parity Conservation • R-parity is a new quantity defined by: • All SM particles have R-parity 1 but all super partners have -1. • It is this that makes the LSP stable.

  26. Dark Matter • Cosmologists believe most matter is dark matter. • Inferred this from observing motions of galaxys. • No one’s sure what it is.

  27. Dark Matter • If R-parity is conserved then the Lightest Super Partner (LSP) will be stable. • Could explain the Dark Matter in the universe. • Depends on SUSY parameters whether the LSP is a gaugino or a sfermion.

  28. Which LSP? Graph showing regions of different LSP’s. Tan β =2

  29. Proton Decay • The best GUT prediction is 1028 years. • Current best guess is greater than 5.5×1032 years. • SUSY can be used to fix this problem.

  30. Other Advantages of SUSY • Grand Unified Theories (GUTs). • Current understanding is just a low energy approximation to some grand theory. • On a large energy scale all forces and particles should essentially be the same. • Coupling constants should equate at high energy.

  31. Figure (a): Coupling constants in the standard model Figure (b): Coupling constants a GUT based on SUSY

  32. Possible GUTs • The main competitor is a theory based on SU(5) symmetry. • Has 24 gauge bosons mediating a single force. • Others as well like one on SO(10) with 45 bosons!

  33. Conclusions • The Standard Model has problems when considered above the electroweak scale. • Supersymmetry solves some of these problems. • Supersymmetry can also be used to explain cosmological phenomena.

  34. SupersymmetryExperimental Issues and Developments

  35. Outline • Motivation for SUSY (continued) • Detecting SUSY • Current and future searches • Results & constraints so far

  36. Motivation for SUSY • Convergence of coupling constants • Proton lifetime • Dark matter (LSP) • Anomalous muon magnetic moment • Mass hierarchy problem

  37. Convergence of Coupling Constants 1 • In a GUT coupling constants meet at high energy • GUT gauge group must be able to contain SU(3)xSU(2)xU(1) • SU(5) best candidate • Three constants:

  38. Convergence of Coupling Constants 2 Source: Kazakov, D I; arxiv.org/hep-ph/0012288

  39. Dark Matter • A leading candidate is the LSP • SM has R=1 & SUSY has R=-1 • Conservation of R-parity • R-parity conservation ensures SUSY particles only decay to other SUSY particles so LSP is stable

  40. WMAP 1 Source: http://map.gsfc.nasa.gov

  41. WMAP 2 Source: http://map.gsfc.nasa.gov

  42. WMAP 3 • 73% dark matter in universe • Total matter density • Improves prospect of discovery at LHC • Within reach of 1TeV linear collider

  43. WMAP 4 Adapted from: J. Ellis et al, Phys, Lett B 565, 176-182

  44. Anomalous Muon Magnetic Moment • Experiment • Dirac theory: • QED corrections: virtual particles • Deviation from SM of

  45. Anomalous Muon Magnetic Moment 2

  46. Anomalous Muon Magnetic Moment 3 Source: http://arxiv.org/hep-ex/0401008

  47. Who is looking for SUSY particles? • LEP • Tevatron • LHC – from 2007? • ILC • Currently no experimental evidence found • Can only constrain models

  48. LEP Source: http://intranet.cern.ch/Press/PhotoDatabase/

  49. LEP Source: http://intranet.cern.ch/Press/PhotoDatabase/

  50. s-fermion searches • Production • Decay • Events with missing energy

More Related