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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