Supersymmetry searches

As discussed before, SUSY theories introduce the existence of particles at the TeV scale, so these could be already accessible at the \textsf{LHC}.

The search for these particles and the determination of their properties, such as mass, spin, etc. and their coupling becomes of central importance in order to verify the existence of new Physics beyond the SM and to demonstrate the validity of the Supersymmetry theories.

Weak-scale supersymmetry is one of the most studied extensions of the SM and it can solve all the problems mentioned above. In R-parity conserving SUSY models, the LSP, typically the lightest neutralino (\tilde{\chi}_1^0), is stable and therefore a good DM candidate. The experimental search for the superpartners of the SM bottom and top quarks, known as bottom and top s-quarks or simply as s-bottom (\tilde{b}_1) and s-top (\tilde{t}_1), is one of the most active areas in the search for SUSY.
These particles can be relatively light, and therefore Naturalness arguments, introduced to avoid fine tuning in the theory, predict the s-bottom and s-top masses to be a few hundred GeV, which would therefore be produced with sizeable cross sections at colliders, and produce heavy quarks (t and b) in their decays.

The Tevatron and the \textsf{LHC} have active experimental programs searching for supersymmetric particles. Since both of these machines are hadron
colliders — proton-antiproton for the Tevatron and proton-proton for the \textsf{LHC} — their researches are more focused on strongly interacting particles. Therefore, most experimental signatures involve production of s-quarks or gluinos.

Phenomena that are object of the major physical interest for the research of SUSY particles at \textsf{LHC} take place from hard scattering processes between the fundamental constituents of protons i.e. valence quarks, sea quarks and gluons.

In the MSSM R-parity conservation scenario, supersymmetric particles would be produced in pairs providing that the number of superparticles at each stage is conserved and the LSP would be stable. Starting from s-quarks and gluinos, each decay chain will contain one LSP that will leave the detector unseen. This leads to the generic prediction that the MSSM will produce a missing energy signal due to these particles leaving the detector.

Particles originated from such processes are generally characterized by high energy and high transverse momentum p_T. However, partons that do not take part in processes, spectators, also contribute to the event through the production of new particles by hadronization. These secondary processes, described by QCD, are generally indicated as underlying events; they give rise to the production of hadronic jets with low transverse momentum p_T and they represent a background to the search for signals of new Physics.

See also ProductionDecay chains and A possible return on race.

 

References and further readings:
S. Baer and X. Tata, Weak Scale Supersymmetry, (Cambridge University Press), 2006
R.H. Mohapatra, Unification and Supersymmetry: the Frontiers of Quark-Lepton Physics – Third Edition, (Springer-Verlag), 2002.
Aitchison I.J.R., Supersymmetry in Particle Physics, (Cambridge University Press).
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