Study of the gauge mediation signal with nonpointing photons at the CERN LHC

We study the gauge mediation signal with the ATLAS detector at the CERN LHC. We focus on the case where the NLSP is the long-lived lightest neutralino (chi/sub 1//sup -0/) which decays dominantly into a photon (gamma) and a gravitino (Gmacron). A nonpointing photon from the neutralino decay can be detected with good position and time resolutions by the electromagnetic calorimeter (ECAL), while the photon momentum would be precisely measured if the photon is converted inside the inner tracking detector before reaching the ECAL. A new technique is developed to determine the masses of the slepton (script lmacron) and the neutralino from events with a lepton and a converted nonpointing photon arising from the cascade decay l ~rightward arrowlchi~/sub 1.