Search for an LSP gluino at LEP with the DELPHI detector

The DELPHI Collaboration

doi:doi:10.1140/epjc/s2002-01111-5

2021 Impact factor 4.991

Particles and Fields

Eur. Phys. J. C 26, 505-525 (2003)
DOI: 10.1140/epjc/s2002-01111-5

Search for an LSP gluino at LEP with the DELPHI detector

The DELPHI Collaboration

(Received: 6 November 2002 / Published online: 15 January 2003 )

Abstract
In some supersymmetric models, the gluino ( $\widetilde{{\mathrm g}}$ ) 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 In these models, the missing energy signature of the lightest supersymmetric particle is no longer valid, even if R-parity is conserved.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 $\mbox{$\widetilde{{\mathrm g}} $ }\to\mbox{$\mathrm{q\bar{q}} $ }\mbox{$\widetilde{{\mathrm \chi}}_1^0 $ }$ . Data collected by the DELPHI detector in 1994 at 91.2 GeV have been analysed to search for $\mbox{$\mathrm{q\bar{q}} $ }\mbox{$\widetilde{{\mathrm g}} $ }\mbox{$\widetilde{{\mathrm g}} $ }$ events. No deviation from Standard Model predictions is observed and a gluino mass between 2 and 18 GeV/c² 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^-1. 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 ( $m_{\tilde{{\mathrm q}}_1}$ , $m_{\tilde{{\mathrm g}}}$ ):

$\mbox{$m_{\tilde{{\mathrm t}}_1} $ }>90~\mbox{$\mathrm{GeV}/\mathrm{c}^2 $ }$ , and $\mbox{$m_{\tilde{{\mathrm b}}_1} $ }>96~\mbox{$\mathrm{GeV}/\mathrm{c}^2 $ }$ for purely left squarks.

$\mbox{$m_{\tilde{{\mathrm t}}_1} $ }>87~\mbox{$\mathrm{GeV}/\mathrm{c}^2 $ }$ , and $\mbox{$m_{\tilde{{\mathrm b}}_1} $ }>82~\mbox{$\mathrm{GeV}/\mathrm{c}^2 $ }$ independent of the mixing angle.