Where is SUSY?

Recent information from the LHC experiments, the relatively low mass of the new boson and other data coming from experiments looking for dark matter worldwide are placing new constraints on the existence of supersymmetry (SUSY). However, there is a large community of scientists that still believes that SUSY particles are out there. Like lost keys at night, perhaps we have been looking for SUSY under the wrong lamp-posts…


Can you work out this rebus? Source: Caroline Duc.

So far, SUSY is “just” a theoretical physics model, which could solve problems beyond the Standard Model by accounting for dark matter and other phenomena in the Universe. However, SUSY has not been spotted so far, and might be hiding because of features different from what physicists previously expected. “Currently, there is no evidence for SUSY, but neither has any experimental data ruled it out. Many searches have focused on simplified versions of the theory but, given the recent information we are gathering from experiments, theorists should rethink the way we are looking for it and the ways we should search for it in the future,” says John Ellis, professor at King’s College London and visiting professor in CERN’s Theory Group. “Maybe SUSY is hiding under a different experimental lamp-post; perhaps one we passed by, perhaps one further down the LHC road.”

A recent paper on SUSY was submitted to the European Journal of Physics C by a group of scientists including John Ellis: “We have combined information coming from CERN’s ATLAS, CMS and LHCb experiments," he continues, "as well as the XENON100 dark matter search, assuming that the new boson discovered with a mass around 125 GeV is indeed the Higgs boson. In the paper we discuss how this information can be combined to give new estimates of the masses of the supersymmetric particles. Before the advent of the LHC, low-energy data, in particular from muon (g-2) experiments, gave hope that SUSY might be discovered at the LHC within its first year of operation. This has not been the case.”

Does this mean that the LHC will not be able to find SUSY if it exists? “No,” replies John Ellis. “If the newly discovered boson is indeed the Higgs boson, some SUSY particles could still be accessible to the LHC experiments.” In other words, the search for SUSY is still open, even though data indicate that the masses involved are higher than originally expected. “If the masses of SUSY particles are in the lower or medium part of the range still allowed in simplified models, we could hope to discover them at the LHC operating close to its design energy of 14 TeV, otherwise we might need a different experimental tool,” explains John Ellis.

And let’s not forget that SUSY might also be discovered “indirectly” as deviations of known particles from their expected Standard Model behaviour could suddenly point scientists to where SUSY is. There are still many lamp-posts to look under!

by Antonella Del Rosso