Testing supersymmetry at future high energy colliders, in dark matter and high precision experiments

• Online Access: http://hdl.handle.net/2047/D20382015

The observation of the Higgs boson at 125 GeV indicates that the size of weak scale supersymmetry lies in the TeV region which makes the discovery of supersymmetry at the LHC more challenging. Here we discuss the potential for the discovery of sparticles and of heavier Higgs bosons at HL-LHC and also argue in favor of construction of a machine with higher energy, i.e., a 27 TeV high energy LHC (HE-LHC). We carry out a comparative study for the discovery of electroweakinos and heavier Higgs bosons at the two machines. For a number of test model points, it is found that the discovery of sparticles (or of heavier Higgs) would require a HL-LHC run between 5$-$8 years while the same parameter points can be discovered in a period of few weeks to $\sim 1.5$ yr at HE-LHC. The analysis indicates that the HE-LHC possibility should be seriously pursued as it would significantly increase the discovery reach for sparticles and for heavier Higgs beyond the reach of HL-LHC and decrease the run period for discovery for models which are also discoverable at HL-LHC. In this work we also discuss the possibility of detecting hidden sector dark matter at the LHC. Specifically we analyze the case when the dark matter resides in the hidden sector while a charged sparticle is the LSP of MSSM. We show that for the case when the portal to the hidden sector is via gauge kinetic mixing and Stueckelberg mass mixing generating feeble interactions between the visible sector and the hidden sector, the charged LSP of MSSM will decay into the hidden sector dark matter. In this case the charged particle will be long-lived and will leave a track inside the detector. We considered two cases: (i) a stau which produces a track but decays inside the detector and can be identified as a decaying particle with missing energy, (ii) a stop which produces an $R$-hadron and decays outside. Each case points to a hidden sector dark matter. For the case (ii) future detectors such as MATHUSLA and FASER will explore the lifetime frontier and are capable of detecting long-lived particles such as the stop which decay further away from their production vertex and they will provide further test of the hidden sector dark matter models. We show that models where the dark matter resides in the hidden sector require both the freeze-out and the freeze-in mechanisms to produce the desired amount of dark matter consistent with the Planck experiment. We also show that the existence of a hidden sector can expand the parameter space of natural supersymmetry. Finally we discuss how precision physics provides another avenue for the exploration of new physics beyond the standard model.--Author's abstract