Photoproduction of theΘ+resonance on the nucleon in a Regge model

Abstract

We estimate the reaction mechanisms for the photoproduction of the 1540 resonance on the nucleon, through K and K Regge exchanges. We compare the size of the cross sections for the n ! K ÿ and p ! K 0 reactions and investigate their sensitivity to the spin-parity assignments J P 1 2; 3 2 for the resonance. The model allows one to estimate the cross sections corresponding with a given upper bound on the width of the . Within this model, the cross sections on the neutron are found to be around a factor of 5 larger than the ones on the proton, due to the presence of charged K exchange for the reaction on a neutron target. Furthermore, the photon asymmetry is found to display a pronounced sensitivity to the parity of the , making it a very promising observable to help determine the quantum numbers of the resonance.

Neutron anomaly inγN→ηNand the flavour SU(3) symmetry

“…[46] with the tiny result for the cross section in the sub-nanobarn range -too small to be observable even with the large CLAS statistics. However, the interference cross section is linear in the Θ + coupling and hence can be substantially larger.…”

“…However, they may be essential, e.g., for comparisons of Θ + -photoproduction off the proton and/or the neutron. In the works [43,44,46] we estimate the coupling of the K * vector meson to the N → Θ + transition employing unitary symmetry, vector meson dominance, and results from the GRAAL Collaboration for η photo-production off the neutron. Our small numerical value for the coupling constant is consistent with the non-observation of the Θ + in recent CLAS searches for its photo-production.…”

“…[46] to estimate the production cross section of Θ + in photo-reactions. With a Θ + -width of 1 MeV and the above value of f 2 (K * N Θ), calculations [46] find small cross sections σ tot (γp → K 0 Θ + ) < 0.22 nb and σ tot (γn → K − Θ + ) < 1 nb, which are below the limits given recently by the CLAS Collaboration.…”

VECTOR AND AXIAL-VECTOR STRUCTURES OF THE Θ+

“…Ref. [16] has kept the tensor coupling constant finite but dropped out the vector coupling constant.…”

Search forΣ50,N50, andΘQiang1, Annand2, Arrington3 et al. 2007Phys. Rev. C10080View full textAdd to dashboardCite

“…This paper reports on a high-resolution search at forward production angles for the Σ ++ as narrow resonances in the missing mass spectra of the re-actions ep → eK + X, ep → eπ + X and ep → eK − X, respectively. The measurements covered a limited range of small scattering angles, which did not allow a partialwave analysis; however, both experimental indications [4] and theoretical expectations [13] are for the Θ + cross section to be forward peaked. One of the interesting features of the reported observations of the Θ + is that the measured width was either an upper limit from the experimental resolution or consistent with having a negligible width [5].…”