Search for an LSP gluino at LEP with the DELPHI detector

TL;DR

This paper searches for light, stable gluinos predicted by supersymmetric models using DELPHI detector data, setting new mass limits and excluding certain parameter regions based on the absence of observed deviations from the Standard Model.

Contribution

First experimental search for light, stable gluinos and R-hadrons at LEP, establishing new mass exclusion limits and constraining supersymmetric model parameters.

Findings

Excluded gluino masses between 2 and 18 GeV/c^2 at 95% CL.

Set lower bounds on squark masses: m_t1 > 90 GeV/c^2, m_b1 > 96 GeV/c^2.

Observed data consistent with Standard Model predictions.

Abstract

In some supersymmetric models, the gluino 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 In these models, the missing energy signature of the lightest supersymmetric particle is no longer valid, even if R-parity is conserved.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 gluino -> q qbar \tilde{\chi}_1^0. Data collected by the DELPHI detector in 1994 at 91.2 GeV have been analysed to search for (q qbar gluino gluino) events. No deviation from Standard Model predictions is observed and a gluino mass between 2 and 18 GeV/c^2 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{q_1},m_gluino): m_\tilde{t_1} > 90 GeV/c^2, and m_\tilde{b_1} > 96 GeV/c^2 for purely left squarks. m_\tilde{t_1} > 87 GeV/c^2, and m_\tilde{b_1} > 82 GeV/c^2 independent of the mixing angle.