Search for new quarks suggested by the superstring

We discuss the possible phenomenology of the additional charge (-1/3) colour triplet particles D1/2 of spin 1/2 and D0, anti D0c of spin 0 which are contained in each matter generation if the superstring is compactified on a Calabi-Yau manifold. In the minimal model with no intermediate mass scales and supersymmetry breaking fed into the observable sector via a gaugino mass, either a spin-1/2 or a spin-0 D particle could be the lightest, and either could be as light as the present lower bound from e+e- experiments of about 20 GeV. The D particles could behave as leptoquarks coupling to quarks and leptons, in which case the single production process ep → D0(anti D0c)+X would occur, and D0(anti D0c) → lq, D1/2 → lq χ tilde decays would dominate, where χ tilde is the lightest supersymmetric particle. Alternatively, the D particles could behave as diquarks coupling to pairs of antiquarks, in which case the single production process anti pp → D0(anti D0c, anti D0, D0c)+X would occur, and D0(anti D0c) → anti qanti q, D0c(anti D0) → qq, D1/2 → anti qanti q χ tilde decays would dominate. We present cross sections for ep → D0(anti D0c)+X, anti pp → D0(anti D0c, D0c, anti D0)+X, e+e- → D0anti D0(D0canti D0c) and D1/2anti D1/2, anti pp → D0anti D0(D0canti D0c) and D1/2anti D1/2+X. We calculate the experimental signals and estimate backgrounds for D production and decay in these processes. The decays D0(anti D0c) → lq and D1/2 → lq χ tilde or anti qanti q χ tilde would be detectable in most of these reactions, but D0(anti D0c) → anti qanti q decays may only be detectable in e+e- → D0anti D0(D0canti D0c) collisions. (orig.)