Tracking down the elusive charginos / neutralinos through $τ$ leptons at the Large Hadron Collider

Abstract

An unconstrained minimal supersymmetric standard model with the superpartners of the strongly interacting particles very heavy (close to the kinematic reach of the LHC or even beyond it) and a relatively light electroweak sector is considered. Using the event generator Pythia it is shown that the 1$τ$-jet (tagged) + 2$l$ and 2$τ$-jets (tagged) + 1$l$ signals with a reasonably hard $\etslash$ spectrum either by themselves or in combination with the conventional $3l$ signal, which is known to be of rather modest size with a soft $\etslash$ spectrum, may appreciably extend the reach of chargino-neutralino search at the LHC with 10 fb$^{-1}$ of integrated luminosity. This is especially so if the lighter chargino and the second lightest neutralino decays via two body leptonic modes with large BRs. The theoretical motivation of this scenario, yielding large values of the fine-tuning parameters but consistent with various indirect constraints including the dark matter relic density, is briefly discussed. It is shown that in the minimal supergravity (mSUGRA) model with an universal scalar mass at the GUT scale, the signals involving $τ$-jets are not viable. Theoretically well-motivated variations of these boundary conditions are, however, adequate for reviving these signals.