Jonathan Nistor Purdue University 1

 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)  super string 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) 2

 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 3

 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 a virtual fermion-antifermion pair Higgs boson dissociating into a virtual sfermion-antisfermion pair 4

 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 right- handed fermions, why?  Drastically increases the parameter space!  124 parameters  Solutions? Work with constrained models cMSSM mSUGRA! Down to only 5 parameters! 5

 R-Parity – a multiplicative quantum number  R= +1(SM particles)  R= –1(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  Good dark matter candidate ! Production of pair of neutralinos R=(+1)(-1)(-1) 6

7  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

 Experiment performed within the framework of mSUGRA  Assumed R-Parity consv. 8 At the Fermilab Tevatron Collider Gluino production squark production

Squark/gluino production: 9 At the Fermilab Tevatron Collider

Multijet-plus-E T Signature  If squarks much lighter than gluinos  squark-squark production enhanced  squark decay:  dijet signature with missing E T  If gluinos lighter than squarks  gluino-gluino process dominates  Gluino decay:  Large number of jets  missing E T 10 At the Fermilab Tevatron Collider

11 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

 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 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… 12