The Search for Supersymmetry Melvin Eloy Irizarry PHY 599
Outline
What is supersymmetry? Standard
Model of particle physics Supersymmetry overview
Where are the superpartners? Experimental
hunt for supersymmetric particles
Why bother with supersymmetry? SUSY
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could answer some questions
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What is supersymmetry?
Standard model of particle physics
6 quarks and 6 leptons Force messengers
W and Z bosons, photons and gluons
Antiparticles Higgs (?)
Image courtesy of DESY 7 March 2007
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Fermions and Bosons Quantum number s – Spin Integer values of s are bosons Half-integer values of s are fermions
Quarks
and leptons are fermions Messenger particles are bosons
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The truth about Supersymmetry… Proposed in the early 1970s “The idea that at a fundamental level the laws of nature are invariant if fermions and bosons are interchanged” For each fermion (boson) there is a superpartner boson (fermion)
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Supersymmetric trivia
Introduces a generalization of spacetime called superspace Spacetime
dimensions + fermionic dimensions
We can have more than one supersymmetry in a given theory Number of fermionic dimensions is always a power of 2
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Minimal supersymmetric Standard Model (MSSM) Proposed in 1981 Assigns a yet-undiscovered partner to each of the known elementary particles of the Standard Model R-Parity is imposed in the MSSM Existence of a stable Lightest Super Partner (LSP) Supersymmetry must be broken
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R-Parity
Let L be the lepton quantum number, B the baryon quantum number and s the spin quantum number PR is 1 for SM particles and -1 for superpartners Multiplicative symmetry
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Supersymmetric interactions
plus
G.L. Kane 2000 7 March 2007
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Elementary particles quark
Superpartners squark
electron neutrino muon tau photon W-boson & Z-boson gluon Higgs boson graviton
Linear superposition are called Neutralinos Charginos
Lightest neutralino is a dark matter candidate
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Where are the superpartners?
Supersymmetric signal Superpartner must be produced in pairs (R-parity) After decay LSPs remain These LSPs do not have color nor electric charge They will escape the detector, leaving a missing energy trail Missing energy will be larger than in SM events
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CDF – Heavy quarks
Top and bottom squarks have large relatively production cross section in the Tevatron
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Bs meson oscillation Bs is a meson made of a bottom quark and a strange antiquark In September 2006 it was announced by CDF the discovery of antimatter-matter transitions at a rate of 3 trillion times per second This rules out some supersymmetric models… but not all!
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DØ – Chargino and neutralino production
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DØ
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LHC Proton-proton collision of 7 TeV per beam High energy collisions in mid 2008 SUSY breaking around LHC probing scale R-parity conservation – LSP and missing energy Higgs ???
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Why Supersymmetry?
Cold Dark Matter
Just after the big bang there were all kind of particles (photons, neutrinos, quarks, electrons, superpartners) Quarks combined to make baryons, then electrons and baryons make atoms Photons and neutrinos remain about the same Superpartners decay into the lightest superpartner (LSP), assumed to be stable Relic calculations of LSP density agree with amount of cold dark matter in the universe
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Higgs mass renormalization
First order corrections to Higgs mass squared are quadratically divergent This arises from Standard Model loop graphs Supersymmetric theories can cancel this divergence with the corresponding superpartner loop graphs Resultant correction is limited by how partnersuperpartner masses differ (SUSY breaking) SUSY breaking scale should be around 1 TeV
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Unification Couplings of interactions appear to met Under supersymmetry coupling strengths appear to meet in a more convincing way
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Conclusion Supersymmetry relates bosons to fermions, doubling the number of particles in the Standard Model No experimental data supports it… yet Hopefully all will be settled when the LHC turns on around 2008 (or the Tevatron gets lucky)
Kane, G. L. Supersymmetry: what? why? when? Contemporary Physics, 2000; vol. 41, num. 6, p 359 – 367 Wikipedia Schwarz, Patricia and John Schwarz Special Relativity: from Einstein to Strings Cambridge 2004 hep-ex/0605005 hep-ex/0609040 hep-ex/0504032
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More references Search for Direct Pair production of scalar top and scalar bottom quark in protonantiproton collisions at 1.96 Tev , CDF – Fermilab http://www-cdf.fnal.gov/physics/exotic/r2a/ 20060622.stopsbottom/ Thanks to Julia Novak
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Standard Model Interactions
G.L. Kane 2000 7 March 2007
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Heavy quarks - details Mass eigenstates of scalar quarks are a mixture of weak eigenstates Splitting of mass eigenvalues depends
Top
scalar quark – large mass of t, large Yukawa coupling Bottom scalar quark – large tan(β)
Likely that lighter stop and sbottom be much lighter compare to other flavor squarks
Mar 7, 2007 - 4. Standard model of particle physics. â 6 quarks and 6 leptons. â Force messengers. â W and Z bosons, photons and gluons. â Antiparticles. â Higgs (?) ... a strange antiquark. â In September 2006 it was announced by. CDF the discovery of antimatter-matter transitions at a rate of 3 trillion times per.
Jun 21, 2001 - Editor: P.V. Landshoff. Abstract. Inspired by .... left-handed electron. (1). eL = 1. F. (( ... electron is the superpartner of a selectron. Lattice sim-.
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D. I. Kazakov. BLTP, JINR, Dubna and ITEP, Moscow .... Page 3 of 48. Kazakov, Supersymmetry in Particle Physics, The Renormalization Group Viewpoint.pdf.
Jun 21, 2001 - phase, i.e., with a gauge symmetry broken by means of the Higgs mechanism and the theory in the confine- ment phase, i.e., a theory with ...
Page 3 of 86. Salam, Strathdee, Supersymmetry and Superfields.pdf. Salam, Strathdee, Supersymmetry and Superfields.pdf. Open. Extract. Open with. Sign In.
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