Supersymmetry is an extension to the Standard Model of particle physics that postulates the existence of additional massive, weakly-interacting particles ("supersymmetric particles" or "sparticles"). Dubbed "the last spacetime symmetry", every matter particle (fermion) in the Standard Model gains a complementary force-carrying (bosonic) sparticle, and every boson gains matter-like supersymmetric fermion. Some therefore see supersymmetry as a way of mathematically unifying matter and forces. Supersymmetry also helps to resolve some problems with the Standard Model; sparticles also provide candidates for the elusive "dark matter" thought to make up some fifth of the known Universe.

However, there is as yet no firm experimental evidence for supersymmetry. It is hoped that sparticles may be created in LHC collisions. Physicists at Imperial College are involved in the search for potential evidence of sparticle production with the CMS detector. In particular:

  • Dr Pieter Everaerts is co-convener of the CMS SUSY physics group (2019-present);
  • Imperial College physicists are involved in many of the CMS SUSY physics analyses;
  • Imperial College HEP group phenomenologists are working on the boundary between supersymmetric theory and experiment, notably on the MasterCode project.

3-jet candidate SUSY event as seen by the CMS detector
3-jet candidate SUSY event as seen by the CMS detector, Oct 2010. Credit: CMS

Exotic physics is typically used as an umbrella term for an experimental search programme that looks for evidence of rare new physics processes beyond the standard model of particle physics. The programme of Exotic searches within the CMS experiment is very broad and aims to cover as many experimentally viable signatures as possible. Typically, the focus is on non-supersymmetric models, such as Extra Dimensions and mini Black Holes, Dark Matter, Hidden Valley models, extended Higgs models, and Compositeness, to name just a few.

Within the Imperial HEP group, our studies are currently focused on searches involving unusual experimental signatures that may arise from as-yet-unseen Long-Lived Particles. These atypical signatures may arise in many of the data sets collected by the CMS experiment, including some special data sets that are unique to CMS, such as a dedicated “BParking” sample of 10 billion B hadron decays (and potentially new physics processes).

A simulated CMS collision that produces a long-lived particle
A simulated CMS collision where a long-lived particle is produced together with other “regular” jets. The long-lived particle may travel “incognito” for a short distance before it decays, creating visible particles that originate from a point in space away from the LHC beam collision point.