Production of Θ+(1540) and Ξ pentaquark states in proton–proton interactions

Abstract

The production of strange pentaquark states (e.g. Theta baryons and Ξ −− states) in hadronic interactions within a Gribov-Regge approach is explored. In this approach the Θ + (1540) and the Ξ are produced by disintegration of remnants formed by the exchange of pomerons between the two protons. We predict the rapidity and transverse momentum distributions as well as the 4π multiplicity of the Θ + , Ξ −− , Ξ − , Ξ 0 and Ξ + for √ s = 17 GeV (SPS) and 200 GeV (RHIC). For both energies more than 10 −3 Θ + and more than 10 −5 Ξ per pp event should be observed by the present experiments.Very recently in photon-nucleus [1,2] and Kaon-nucleus experiments [3] a new baryon, consisting of five quarks, uudds, has been identified in the K + n or K 0 p invariant mass spectrum. It has been been named Θ + particle and has spin 1/2, isospin 0 and strangeness +1. Its mass is about 1.54 GeV and its width is less than 25 MeV. Such a state has been predicted by Diakonov [4] in the framework of a chiral soliton model. This finding has renewed the experimental and theoretical interest for novel baryon states. Major progress has been reported on a possible extension of the original model [5,6], within the Skyrme model [7][8][9], and within the constituent quark model [10,11]. Also (lattice) QCD studies of the Θ + (see e.g. [12][13][14]) have been performed and first explorations of the Θ + multiplicity at SPS and RHIC energies are available [15][16][17]. Thus, the existence of this novel state has many perspectives for pp as well as for nucleus-nucleus collisions.In this letter, we present predictions for the Θ + in pp collisions from a newly developed approach for hadronic interactions. It has recently been shown [18] that the standard string fragmentation models which described spectra and multiplicities of many hadrons rather well need to be revised: due to their diquark-quark topology these models produce more Ω than Ω in medium and low energetic pp interactions, in contradistinction to experiments. Therefore a key issue is presently to gain information on the details of hadron production. Espe- * Alexander von Humboldt Fellow cially more exotic states like the Λ(1405) which may be a udsuu state or the Θ + carry important information to tackle this question. If their multiplicity can be related to that of other particles one can hope to get experimentally a handle on the hadronization process.In heavy ion collisions the multiplicity of the most abundant particles can be well described in a statistical model assuming a temperature close to that where the chiral/confinement phase transition is expected and a moderate chemical potential. Unstable particles can test how the expanding system interacts afterwards because if the decay products have still an interaction in the invariant mass spectra the resonance cannot be identified anymore. Especially long living states are very useful in this respect.Until this year, the search for multi-quark bags focused mainly on the H-particle [19], because it is closely related to the study of Ξ an...

Productions of hadrons, pentaquarksΘ+andΘ*++, and di-baryonShao1, Xie2, Wang3 2005Phys. Rev. C

“…Our estimates for Θ + and Θ * ++ are shown in [89,90]. For comparison, the yield of Θ + in proton-proton collision is predicted to be about 10 −2 − 10 −3 [92,93].…”

Production of the pentaquark Θ+ in np scattering

“…There exist already investigations on the production of the in the NN interaction [27][28][29][30]. References [28,29] are concerned with the prediction of the total cross sections and Ref.…”

“…References [28,29] are concerned with the prediction of the total cross sections and Ref. [30] has explored the production in high-energy pp scattering. In the present work, we want to investigate the np !…”

Review of the experimental evidence on pentaquarks and critical discussion

“…The current theoretical description of pentaquarks (e.g. [3,24,25,26,27,28,29,30,31]) does not lead to a unique picture on the pentaquark existence and characteristics, reflecting the complexity of the subject. In the following, we review and discuss the experimental observations of pentaquark candidates, as well as their lack of observation by some experiments.…”