Jonathan Nistor
Purdue University
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 A symmetry relating elementary particles together in pairs whose
respective spins differ by half a unit  superpartners
 Provides a pairing between fermions and bosons
 A quantum symmetry of space-time (No classical analog!)
 Supersymmetry algebra first discovered in late 1960s (most general extension of
Poincare group)
 Subsequently applied to “bosonic” string theory to incorporate fermionic patterns
of vibration (1971)
 superstring theory is born
 First applied to the field of Particle Physics by Julius Wess and
Bruno Zumino (1973)
 By early 1980’s, several supersymmetric SM had been proposed (MSSM)
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
Allows for unification of the
couplings strengths at grand unification
scale

Offers a good candidate for cold dark
matter (a bit more on this one later…)

Predicts light Higgs Boson
MSSM  mh≤ 135 GeV
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 SUSY stabilizes the quadratic divergences in
the Higgs mass
 Fermion/boson pairing leads to “cancellation”
of similar Feynman loop diagrams
 Same vertices
 Same coupling constants
Higgs boson dissociating into a
virtual fermion-antifermion pair
 Amplitudes have “equal” magnitude
 Opposite sign
 SUSY is a broken symmetry – How broken?
 sparticle masses must be < ~1 TeV to maintain
cancellations
Higgs boson dissociating into a
virtual sfermion-antisfermion pair
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
Double the number of particles?

Five Higgs bosons:

Postulate superpartner for each SM
particle with identical coupling
strengths
Must also distinguish between left-handed and righthanded fermions, why?

Drastically increases the parameter space!
 124 parameters

Solutions? Work with constrained models
cMSSM
mSUGRA! Down to only 5 parameters!
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 R-Parity – a multiplicative quantum number
 R= +1
 R= –1
Production of pair of neutralinos
(SM particles)
(SUSY particles)
 R-Parity conservation – At every vertex the R-product
must be + 1
 Implications of R-Parity conservation
 Every SUSY interaction must involve two
SUSY particles
 SUSY particles created in pairs
 a SUSY particle decays into another SUSY particle
and SM particles
 Lightest sparticle (LSP) cannot decay  WIMP
R=(+1)(-1)(-1)
Good dark matter candidate !
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 SUSY provides compelling arguments for investigations of the TeV scale
 No evidence for sparticles has been found so far
 constraints on various models
 establishes lower bounds on the masses
 The Large Hadron Collider (LHC) promises to explore directly TeV
energy range.
 Low–Energy SUSY may be as risk
 CDF detector in Tevatron Run II
 Recent results on a search for gluino and squark production
 New limits on the gluino and squark masses were established
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At the Fermilab Tevatron Collider


Experiment performed within
the framework of mSUGRA
Assumed R-Parity consv.
squark production
Gluino production
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At the Fermilab Tevatron Collider
Squark/gluino production:
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At the Fermilab Tevatron Collider
Multijet-plus-ET Signature


If squarks much lighter than gluinos
 squark-squark production enhanced
 squark decay:
dijet signature with missing ET
If gluinos lighter than squarks
 gluino-gluino process dominates
 Gluino decay:
Large number of jets
missing ET
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At the Fermilab Tevatron Collider
Results:
 Observed events matched SM expected
events
 No significant deviation
 Data provided exclusion limits on
gluino/squark production
 eg. Excluded gluino masses up to 280
GeV for every squark mass
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
SUSY, “the best motivated scenario today for physics beyond the SM?”
Many motivations for recasting of the SM into a SUSY framework

Currently no experimental evidence that nature obeys SUSY

Future prospects

 LHC’s discovery potential extends up to squark/gluino masses of 2.5 -3 TeV
 If nothing is found at LHC  Low-energy SUSY will lose most of its motivation
No longer able to stabilize Higgs mass
 On the other hand…
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