Search for pentaquark states in Z decays

Exotic hadrons made of five quarks (pentaquarks) are searched for in hadronic Z decays collected by the ALEPH detector at LEP. No significant signal is observed. At 95% C.L., upper limits are set on the production rates N of such particles and their charge-conjugate state per Z decay: N Theta(1535)+ . BR(Theta(1535)^+ -> pK0s xi^- pi^-) Xi^-pi^+ D*-p) D^-p) < 31 x 10^-4.