Kaluza-Klein gravitino production with a single photon at e ⁺e^- colliders

In a supersymmetric large extra dimension scenario, the production of Kaluza-Klein gravitinos accompanied by a photino at e⁺e^- colliders is studied. We assume that a bulk supersymmetry is softly broken on our brane such that the low-energy theory resembles the MSSM. Low energy supersymmetry breaking is further assumed as in GMSB, leading to a sub-eV mass shift in each KK mode of the gravitino from the corresponding graviton KK mode. Since the photino decays within a detector due to the sufficiently large inclusive decay rate of γ̃ → γḠ, the process e ⁺e^- γ̃ Ḡ yields single photon events with missing energy. Even if the total cross section can be substantial at √s = 500 GeV, the KK graviton background of e⁺e^-→ γG is kinematically advantageous and .thus much larger. It is shown that the observable Δσ_LR = σ( can completely eliminate the KK graviton background but retain most of the KK gravitino signal, which provides a unique and robust method to probe the supersymmetric bulk.