2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/204339The quark model does not exclude states composed of more than three quarks, like pentaquark systems. Controversial evidence for such states has been published in the last years, in particular: for a strange pentaquark Theta(1540)+; for a double-strange state, the Xi(1862)--, subsequently called Phi(1860)--; and for a charmed state, the Theta_c(3100)^0. If confirmed, a full pentaquark family might exist; such pentaquark states could be produced in e+e- annihilations near the Z energy. In this paper a search for pentaquarks is described using the DELPHI detector at LEP, characterized by powerful particle identification sub-systems crucial in the separation of the signal from the background for these states. At 95% CL, upper limits are set on the production rates <N> of such particles and their charge-conjugate state per Z decay: <N_Theta+> x Br(Theta+ -> pK0_S) < 5.1 x 10^{-4} <N_Theta++> < 1.6 x 10^{-3} <N_Phi(1860)-- > x Br(Phi(1860)-- -> Xi- pi-) < 2.9 x 10^{-4} <Theta_c(3100)^0> x Br(Theta_c(3100)^0 -> D*+ pbar) < 8.8 x 10^{-4} .15 pages, 5 figures, Accepted by Phys. Lett. BHigh Energy Physics - Experimenttext