A light sneutrino rescues the light stop

Abstract

Stop searches in supersymmetric frameworks with R-parity conservation usually assume the lightest neutralino to be the lightest supersymmetric particle. In this paper we consider an alternative scenario in which the left-handed tau sneutrino is lighter than neutralinos and stable at collider scales, but possibly unstable at cosmological scales. Moreover the (mostly right-handed) stop overset{sim }{t} is lighter than all electroweakinos, and heavier than the scalars of the third generation lepton doublet, whose charged component, overset{sim }{tau } , is heavier than the neutral one, overset{sim }{nu } . The remaining supersymmetric particles are decoupled from the stop phenomenology. In most of the parameter space, the relevant stop decays are only into toverset{sim }{tau}tau , toverset{sim }{nu}nu and boverset{sim }{nu}tau via off-shell electroweakinos. We constrain the branching ratios of these decays by recasting the most sensitive stop searches. Due to the “double invisible” kinematics of the overset{sim }{t}to toverset{sim }{nu}nu process, and the low efficiency in tagging the toverset{sim }{tau}tau decay products, light stops are generically allowed. In the minimal supersymmetric standard model with ∼ 100 GeV sneutrinos, stops with masses as small as ∼ 350 GeV turn out to be allowed at 95% CL.