Abstract
A search for chargino, neutralino and scalar lepton pair-production in e+e- collisions at the centre-of-mass energy of 189 GeV is performed under the assumptions that R-parity is not conserved in decays and only one of the coupling constants lambda_ijk, lambda'_ijk or lambda''_ijk is non-negligible. No signal is found in a data sample corresponding to an integrated luminosity of 176.4 pb-1. Limits on the production cross sections, on the Minimal Supersymmetric Standard Model parameters and on the masses of the supersymmetric particles are derived.
Highlights
The most general superpotential of the Minimal Supersymmetric Standard Model (MSSM) [1], which describes a supersymmetric, renormalizable and gauge invariant theory, with minimal particle content, includes the term WR [2, 3]: WR = λijkLiLj Ek + λijkLiQj Dk + λijkUiDj Dk, (1)where λijk, λijk and λijk are the Yukawa couplings and i, j and k the generation indices; Li and Qi are the lefthanded lepton- and quark-doublet superfields, Ei, Di and Ui are the right-handed singlet superfields for charged leptons, down- and up-type quarks, respectively
In order to prevent the simultaneous presence of identical fermionic fields, the following antisymmetry relations are required: λijk = −λjik and λijk = −λikj, reducing to 9 + 27 + 9 the total number of independent Yukawa couplings
The simultaneous presence of L- and B-violating terms would lead to a fast proton decay1 [4]
Summary
Terms is enough to prevent a fast proton decay, there is no need to impose a priori R-parity conservation. Two new kinds of processes are allowed: single production of supersymmetric particles, or LSP decays into Standard Model particles via scalar lepton or quark exchange. In the latter case, the MSSM production mechanisms are unaltered by the operators in (1). Searches for R-parity violating decays of supersymmetric particles were performed by other LEP experiments [10]. If R-parity is conserved, supersymmetric particles can be produced only in pairs and they decay in cascade to the lightest supersymmetric particle (LSP), which is stable [6]. China 1 With contributions at the tree level from λ11kλ11k, and at one-loop level from any product λijkλlmn or λijkλlmn
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