jonathan nistor purdue university 1. a symmetry relating elementary particles together in pairs...
DESCRIPTION
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 m h ≤ 135 GeV 3TRANSCRIPT
Jonathan NistorPurdue 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 bosonsA 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
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 avirtual fermion-antifermion pair
Higgs boson dissociating into avirtual sfermion-antisfermion pair
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Double the number of particles?Five Higgs bosons:
Postulate superpartner for each SM particle with identical coupling
strengthsMust also distinguish between left-
handed and right- handed fermions, why?
Drastically increases the parameter space!
124 parametersSolutions? Work with constrained
modelscMSSMmSUGRA! Down to only 5 parameters! 5
Production of pair of neutralinos
R=(+1)(-1)(-1)
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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 IIRecent results on a search for gluino and squark
production New limits on the gluino and squark masses were
established
Experiment performed withinthe framework of mSUGRA
Assumed R-Parity consv.
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At the Fermilab Tevatron Collider
Gluino production
squark production
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 jetsmissing ET
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At the Fermilab Tevatron Collider
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At the Fermilab Tevatron Collider
Results:Observed events matched SM expectedevents
No significant deviationData provided exclusion limits on gluino/squark production
eg. Excluded gluino masses up to 280
GeV for every squark mass
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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