A diquark model for pentaquark baryons and tetraquark mesons

In the spirit of quark-diquark model, used earlier for the nucleon [Ann. Phys. (N.Y.) 108 (1977) 198] we investigate here some properties of the newly discovered exotic pentaquark systems, viz., theta(+)(1540) and (say) zeta(0)(3099). For this purpose, in the first stage, we consider these multiquark states as three-body systems-two diquarks of (ud)-type and an antiquark with a Coulomb-type color force between them. In the second stage, we replace this three-body system with an effective two-body system in which the two bound diquarks constitute the core and the extra (fifth) antiquark (valence) revolves around this core in a Coulomb field. After accounting for the extended character of the diquark from the earlier work, we compute the form factors for these pentaquark systems and make some remarks about their magnetic moments. Predictions are also made for the form factors of the four-quark (tetraquark) mesons, i.e., for the diquark-antidiquark bound systems. In both theta(+)(1540) and zeta(0)(3099) the valance antiquarks are found to be embedded in the core unlike the case of nucleon. (C) 2004 Elsevier B.V. All rights reserved.