Search for new quarks suggested by the superstring

We discuss the possible phenomenology of the additional charge (- 1 3) colour triplet particles D 1 2 of spin 1 2 and D0,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(D0c) + X would occur, and D0(D0c) → lq, D 1 2 → lqχ decays would dominate, where χ is the lightest supersymmetric particle. Alternatively, the D particles could behave as disquarks coupling (p)p → D0(D0(Dc,D0D0c) + K to pairs of antiquarks, in which case the single production process would occur, and D0(D0c) → qq, D0c(D0) → qq, D 1 2 → qqχ decays would dominate. We present cross sections for ep → D0(D0c + X,ep → D0(D0c) + X, (p)p → D0(D0c, D0c, D0c, D0) + X, e+e- → D0D0(D0c D0c) and D 1 2D 1 2, (p)p → D0D0(D0c D0c and D 1 2D 1 2 + X. We calculate the experimental signals and estimate backgrounds for D production and decay in these processes. The decays D0(D0c) → lq and D 1 2 → lqχ or qqχ would be detectable in most of these reactions, but D0(D0c → qq decays may only be detectable in e+ e- → D0D0(D0cD0c) collisions. © 1987.