We consider analysis targets at the International Linear Collider in which only a single photon can be observed. For such processes, we have developed a method which uses likelihood distributions using the full event information (photon energy and an
gle). The method was applied to a search for neutralino pair production with a photon from initial state radiation (ISR) in the case of supergravity in which the neutralino is the lightest supersymmetric particle. We determine the cross section required to observe the neutralino pair production with ISR as a function of the neutralino mass in the range of 100 to 250 GeV.
