Pentaquark Θ+(1540) production in γN→KK¯N reactions

Abstract

The recent developments in the search of exotic pentaquark hadrons are briefly reviewed. We then focus on investigating how the exotic pentaquark Θ(1540) baryon production can be identified in the γN → KKN reactions, focusing on the influence of the background (non-Θ production) mechanisms. By imposing the SU(3) symmetry and using various quark model predictions, we are able to fix the coupling constants for evaluating the kaon backgrounds, the KK production through the intermediate vector meson and tensor meson photoproduction, and the mechanisms involving intermediate Λ (1116), Λ(1405), Λ(1520), Σ(1193), Σ(1385), and ∆(1232) states. The vector meson photoproduction part is calculated from a phenomenological model which describes well the experimental data at low energies. We point out that the neutral tensor meson production can not be due to π 0 -exchange as done by Dzierba et al. [Phys. Rev. D 69, 051901 (2004)] because of C parity. The neutral tensor meson production is estimated by considering the vector meson exchange and found to be too weak to generate any peak at the position near Θ(1540). For Θ(1540) production, we assume that it is an isoscalar and hence can only be produced in γn → K + K − n and γp → K 0 K 0 p reactions, but not in γp → K + K − p and γn → K 0 K 0 n. The total cross section data of γp → K + K − p is thus used to fix the form factors which regularize the background amplitudes so that the signal of Θ(1540) in γn → K + K − n and γp → K 0 K 0 p cross sections can be predicted.We find that the predicted K + K − and K + n invariant mass distributions of the γn → K + K − n reaction can qualitatively reproduce the shapes of the JLab data. However, the predicted Θ(1540) peak can not be identified unambiguously with the data. High statistics experiments are needed to resolve the problem. We also find that an even-parity Θ is more likely to be detected, while it will be difficult to identify an odd-parity Θ, even if it exists, from the background continuum, if its coupling constants are small as in the present quark model predictions.

K*couplings for the antidecuplet excitation

“…The dominance of the tensor coupling over the vector one in hadronic non-diagonal transitions (between different flavor multiplets) is supported by the analysis [14] of data for transitions between 10 and 8 multiplets. Regretfully, many phenomenological calculations of Θ-production (e.g., [3,4,5,6,7]) have used only the vector coupling for vector-meson exchanges, assuming non-vanishing f a 1 | q 2 →0 and neglecting f a 2 (q 2 ) . To our best knowledge, the dominance of the tensor coupling has been used only in Refs.…”

Interactions and decays of high-spin baryon resonances

“…[17], the main contribution comes from the excitation of intermediate hyperons because of the 02008-p.5 absence of exotic mesons having strangeness S = 2. This feature is very different from the reaction mechanisms of γN → KKN, where the dominant contribution comes from the production of the φ meson [16]. Therefore, Ξ production is a very useful tool to investigate hyperon resonances having S = −1.…”

“…However, this can be done only for g 1 as the previous works were based on the Lagrangian which has only the g 1 term [15,16]. Therefore, here, we assume that g 2 ≈ g 3 ≈ 0.…”

Analysis of recent CLAS data onΣ*(1385) photoproduction off a neutron target

“…Furthermore, the coupling-constant value g KN Λ = −13.24 is an estimate based on flavor SU(3) symmetry relations [6,7,25]. For the u-channel Σ * exchange, the effective Lagrangian for γΣ…”