Selectron Pair Production in e+e- Colliders and the Supergravity Spectrum

Selectrons may be produced in pairs at LEPII if their mass is less than about 100 GeV. Preferably, they decay into the lightest neutralino plus an electron. In a scenario where selectrons are observed at LEPII, we show that: (i) in a first stage where experimental errors are large, the measurement of the total cross section of selectron pair production, the selectron mass, and the lightest neutralino mass, allow us to validate or rule out the Minimal Supergravity Model in its simplest form, and that (ii) in a second stage where precision measurements are available, the value of $\tan\beta$ can be determined together with the rest of the parameters that specify the Minimal Supergravity Model and, with them, the entire supersymmetric spectrum can be calculated. We include experimental constraints from sparticle searches, $Z$--pole physics, stability of the lightest supersymmetric particle (LSP) and the decay $b\rightarrow s\gamma$. In these scenarios, small values of $\tan\beta$ and negative values of $\mu$ are preferred, and the lightest Higgs mass satisfies $m_h<110$ GeV, which makes it likely to be detected at LEPII.