Limits on the mass of a superstring Z′ from the CERN pp̄ collider

We illustrate how recent CERN pp̄ collider data can be used to bound the mass of a possible Z′ in superstring-inspired models. We take into account the fact that the Z′ couplings to quarks and leptons are smaller than those of the conventional Z, and the possibility that the Z′ may be able to decay into exotic particles, thereby suppressing the Z′→ℓ+ℓ- branching ratio. In the minimal rank-five model we find mZ′ > 167GeV if the Z′ can only decay into conventional quarks and leptons and mZ′ > 118 GeV for the least favourable spectrum of three E627 generations of particles and sparticles which is allowed by other experiments. When combined with a global analysis of neutral current data, the latter conservative limit can be increased to mZ′ > 156 GeV. We derive analogous limits for two other superstring-inspired models. We show how these limits can be improved using future FNAL Tevatron and SLC data. © 1988.