pentaquarks in the constituent quark model

The stability of strange pentaquarks uudds is studied in a constituent quark model based on a flavor-spin hyperfine interaction between quarks. With this interaction model, which schematically represents the Goldstone boson exchange interaction between constituent quarks, the lowest lying strange pentaquark is a p−shell state with positive parity. The flavor-spin interaction lowers the energy of the lowest p−shell state below that of the lowest s−shell state, which has negative parity because of the negative parity of the strange antiquark. It is found that the strange pentaquark is stable against strong decay provided that the strange antiquark interacts by a fairly strong spin-spin interaction with u and d quarks. This interaction has a form that corresponds to η meson exchange. Its strength may be inferred from the π 0 decay width of D * s mesons. Renewed interest in the existence of pentaquarks [1,2] has been raised by the recent observation of an S = 1 baryon resonance in photo-production of kaon pairs on neutrons: γn ← K + K − n [3]. This resonance has a peak at 1.54 ± 0.01 GeV/c 2 and a width, which is less than 25 MeV/c 2. It may be interpreted as a strange meson-baryon resonance or as a pentaquark of the form uudds. The expectation has been that stable pentaquarks should be likely to exist in the heavy flavor sectors [1,2,4,5], but experimental searches have remained inconclusive [6,7]. A constituent quark model study of pentaquark states of the form qqqq¯ s, indicates that such states are unstable against strong decay if the only interaction between the strange antiquark and the light flavor quarks is the confining interaction [8]. The prediction of a stable strange pentaquark with positive parity at an the energy close to that of the empirically found resonance was first made with a chiral soliton model, in which it was classified as the lowest state of the baryon antidecuplet multiplet [9]. Here it is shown that once an attractive spin dependent hyperfine interaction between the light flavor quarks and the strange antiquark is introduced, stable positive parity strange pentaquarks may * 2 also be accomodated within the constituent quark model. The originally proposed pentaquarks, which were introduced in the context of the conventional one-gluon exchange model for the hyperfine interaction between constituent quarks, had negative parity, as they represented states with all the light flavor quarks as well as the strange …