Search for pentaquark states in Z decays

A search for exotic baryons containing five quarks has been carried out in hadronic Z decays using the ALEPH detector at LEP I. No significant signal has been found. Preliminary Limits are set, at the 95% confidence level, on the following production rates per hadronic Z decay: N_Theta(1535)(+) < 0.0030 N_Xi(1862)(--)*BR(Xi(1862)(--) -> Xi(-)pi(-) ) < 4*10^(-4) N_Theta_(c)(3100)(0)*BR(Theta(c)(0) -> D(*-)p ) < 6*10^(-4) N_Theta_(c)(3100)(0)*BR(Theta(c)(0) -> D(-)p ) < 25*10^(-4) N_Theta_(c)(3100)(+)*BR(Theta(c)(0) -> Dbar(0)p) < 15*10^(-4) where the charge conjugated states are included in the limits. Also limits on the ratio to non-exotic related particles are obtained: N_Theta(+)/ N_Lambda(1520) < 0.13 N_Xi(1862)(--)/ N_Xi(1530)(0) < 0.06