Long-lived Higgsino pairs decaying within the LHC detectors

Abstract

Pair-produced long-lived lightest Higgsinos decaying within a few meters in the LHC detectors are considered. The relatively light nearly-pure Higgsino states object of this study are those of a supersymmetric minimal model with gauge-mediated supersymmetry breaking and heavy sfermions and gauginos. The heavier Higgsinos decay instantly into the lightest one, with very little activities. Hence, all pair-produced Higgsinos end up as a pair of the lightest neutral Higgsinos, possibly long lived and decaying into the gravitino and either the Higgs or the Z boson. If they decay inside the detectors, these bosons deposit huge energies in the calorimeters. The cross section $σ_2$ ($σ_1$) for the events with two (at least one) decaying-in-flight lightest Higgsinos is examined. The combination $(σ_1)^2/σ_2$ is found to be almost insensitive to the lightest Higgsino lifetime, thereby providing a good variable to measure its mass. The ratio $σ_1/σ_2$, instead, mildly dependent on its mass, can give good information on its lifetime. It is argued that the lightest Higgsinos in the events are rather slow, as the very relativistic ones escape away. Thus, the initial state radiations tend to be soft and a trigger system appropriate for such events is necessary to detect them.