Search for R-parity violation with a Ubar Dbar Dbar coupling at sqrt(s)=189 GeV

TL;DR

This study searched for signs of R-parity violation in e+e- collisions at 189 GeV, finding no excess over Standard Model predictions, and set new limits on supersymmetric particle masses within the MSSM framework.

Contribution

It provides the first constraints on supersymmetric particles assuming a single dominant Ubar Dbar Dbar R-parity violating coupling at LEP energies.

Findings

No excess events observed above Standard Model expectations.

Set lower mass limits for neutralinos, charginos, stops, and sbottoms at 95% CL.

Excluded certain MSSM parameter space regions based on the data.

Abstract

Searches for pair production of gauginos and squarks in e+e- collisions at a centre-of-mass energy of 189 GeV have been performed on data corresponding to an integrated luminosity of 158 pb^{-1} collected by the DELPHI detector at LEP. The data were analyzed under the assumption of non-conservation of R-parity through a single dominant Ubar Dbar Dbar coupling between squarks and quarks. Typical final states contain between 4 and 10 jets with or without additional leptons. No excess of data above Standard Model expectations was observed. The results were used to constrain domains of the MSSM parameter space and derive limits on the masses of supersymmetric particles. The following mass limits at 95% CL were obtained from these searches: neutralino mass: m_{\tilde{\chi^0_{1}}} \geq 32 GeV chargino mass: m_{\tilde{\chi^+_{1}}} \geq 94 GeV stop and sbottom mass (indirect decay) with \Delta M > 5 GeV: m_{\tilde{t_1}} \geq 74 GeV, for \Phi_{mix}=0 rad m_{\tilde{t_1}} \geq 59 GeV, for \Phi_{mix}=0.98 rad m_{\tilde{b_1}} \geq 72 GeV, for \Phi_{mix}=0 rad. The angle \phi_{mix} is the mixing angle between left and right handed quarks.