Prospects for measuring the mass of heavy, long-lived neutral particles that decay to photons

Abstract

We describe a novel way to measure the mass of heavy, long-lived neutral particles that decay to photons using collider experiments. We focus on a Light Neutralino and Gravitino model in a Gauge Mediated Supersymmetry Breaking scenario where the neutralino has a long-lifetime (O(ns)) as it is not excluded by current experiments. To illustrate our method and give sensitivity estimates we use recent CDF results and a production mechanism where sparticles are produced via $\ddot{I}{•}_i\to \tilde{\ddot{I}}{‡}_0^1\tilde{\ddot{I}}{‡}_0^1\to ({\hat{I}}^3\tilde{G})({\hat{I}}^3\tilde{G})$ in which $\ddot{I}{•}_i$ indicates a neutral scalar boson, $\tilde{\ddot{I}}{‡}_0^1$ is the lightest neutralino and $\tilde{G}$ is the gravitino, as a full set of background shapes and rates are available. Events can be observed in the exclusive photon plus Missing $E_T$ final state where one photon arrives at the detector with a delayed time of arrival. Surprisingly, a simple measurement of the slope of the delayed-time distribution with the full CDF dataset is largely insensitive to all but the $\tilde{\ddot{I}}{‡}_0^1$ mass and allows for the possibility of determining its mass to approximately 25% of itself.

16 pages, 6 figures