Testing SUSY

by Prof. Graham Ross (University of Oxford)

Tuesday 30 Mar 2010, 17:15 → 18:15 Europe/Berlin

Max-Planck-Institut für Physik, Auditorium

Supersymmetry (SUSY) is probably the most promising extension of the Standard Model of the strong, electromagnetic and weak interactions. It can explain why the spontaneous symmetry breaking scale of the weak interactions is so much smaller than other fundamental scales of physics such as the Planck scale or the Grand Unified scale (the hierarchy problem) and it leads to a very precise unification of the strengths of the fundamental interactions. However, if SUSY does provides a solution to the hierarchy problem then supersymmetric states should not be too heavy. This requirement is quantified by a fine tuning measure that provides a quantitative test of SUSY. It is also useful in correlating the impact of the various experimental measurements relevant to the search for supersymmetry and also in identifying the most sensitive measurements for testing SUSY. A calculation of fine tuning to two-loop order in the CMSSM allows us to determine the present limits on the CMSSM parameter space and identify the measurements at the LHC that are most significant in covering the remaining space consistent with a given level of fine tuning. Without imposing the LEP Higgs mass bound, the most likely mass, consistent with the dark matter abundance and the non-observation of SUSY states to date, is found to be just above the current limit. Dark matter searches provide a sensitive probe of the lowest fine-tuned points. The extension of SUSY tests to cover the full MSSM parameter space is discussed. For the case of non-universal gaugino masses a second focus point is identified that reduces fine-tuning. As a result there remain significant low-fine-tuned regions of parameter space to be probed by the LHC.