Search for Pentaquarks in the Hadronic Decays of the Z Boson with the DELPHI Detector at LEP

TL;DR

This paper reports a search for pentaquark states in Z boson decays using the DELPHI detector at LEP, setting upper limits on their production rates and contributing to the understanding of exotic hadronic states.

Contribution

It provides the first comprehensive search for multiple pentaquark states in e+e- collisions at LEP energies, establishing upper limits on their production.

Findings

No evidence of pentaquark production was observed.

Upper limits on production rates were established at 95% confidence level.

The results constrain models predicting pentaquark formation in Z decays.

Abstract

The 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} .