Pentaquark Theta(+)(1540) production in gamma N -> K(K)overbar N reactions

摘要

Recent developments in the search of exotic pentaquark hadrons are briefly reviewed. We then focus on investigating how the exotic pentaquark Theta(1540) baryon production can be identified in the gamma N -> K (K) over barN reactions, focusing on the influence of the background (non-Theta 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 K (K) over bar production through the intermediate vector meson and tensor meson photoproduction, and the mechanisms involving intermediate A(I 116), A(1405), A (1520), Sigma(1 193), Sigma(1 385), and A (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 cannot be due to pi(0)-exchange as done by Dzierba et al. [Phys. Rev. D 69 (2004) 051901] 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 Theta(1540). For Theta(1540) production, we assume that it is an isoscalar and hence can only be produced in gamma n K(+)K(-)n and gamma p -> K-0(K) over bar (0)p reactions, but not in gamma p -> K(+)K(-)p and gamma n -> K-0(K) over bar (0)n. The total cross section data of gamma p -> K(+)K(-)p is thus used to fix the form factors which regularize the background amplitudes so that the signal of Theta(1540) in gamma n -> K(+)K(-)n and gamma p -> K-0(K) over bar (0)p cross sections can be predicted. We find that the predicted K+K- and K(+)n invariant mass distributions of the gamma n -> K(+)K(-)n reaction can qualitatively reproduce the shapes of the JLab data. However, the predicted Theta(1540) peak cannot be identified unambiguously with the data. High statistics experiments are needed to resolve the problem. We also find that an even-parity Theta is more likely to be detected, while it will be difficult to identify an odd-parity Theta, even if it exists, from the background continuum, if its coupling constants are small as in the present quark model predictions. (c) 2005 Elsevier B.V. All rights reserved.