Search for an LSP gluino at LEP with the DELPHI detector

In some supersymmetric models, the gluino (\glui) is predicted to be light and stable. In that case, it would hadronize to form R-hadrons. In these models, the missing energy signature of the lightest supersymmetric particle is no longer valid, even if R-parity is conserved. Therefore, such a gluino is not constrained by hadron collider results, which looked for the decay $\glui\to\qqbar\xoi$.\\ Data collected by the DELPHI detector in 1994 at 91.2~GeV have been analysed to search for $\qqbar\glui\glui$ events. No deviation from Standard Model predictions is observed and a gluino mass between 2 and 18~\GeVcc\ is excluded at the 95\% confidence level in these models. Then, R-hadrons produced in the squark decays were searched for in the data collected by DELPHI at the centre-of-mass energies of 189 to 208 GeV, corresponding to an overall integrated luminosity of 609~\pb. The observed number of events is in agreement with the Standard Model predictions. Limits at 95\% confidence level are derived on the squark masses from the excluded regions in the plane (\msqi,\mglui): \begin{itemize} \item[\ ] $\msti>90~\GeVcc$, and $\msbi>96~\GeVcc$ for purely left squarks. \item[\ ] $\msti>87~\GeVcc$, and $\msbi>82~\GeVcc$ independent of the mixing angle.