Λ(1520,3/2−)-photoproduction reaction viaγN→KΛ

Abstract

We investigate Λ(1520, 3/2 − , D 03 ) photoproduction via the γN → KΛ * process. Using effective Lagrangians, we compute the total and differential cross sections. The dependence on the momentum transfer for the photoproduction at the tree-level is also examined. We find that the total cross sections for the proton target are well reproduced as compared with the experimental data. It turns out that the total cross sections for the neutron target are significantly smaller than those for the proton one. We also compare the present results with the γN →KΘ + reaction in order to extract information of Θ + . The role of K * -exchange in the production reaction is also discussed.Recent interest in excited baryons has been largely motivated by new experimental developments [1]: The observation of the exotic Θ + resonance of strangeness S = +1 has triggered diverse activities in both experimental and theoretical studies. The finding of the Θ + has renewed interest in baryon spectroscopy. For instance, properties of the Λ(1405) has been reanalyzed, based on the idea of chiral perturbation theory and of dynamical generation from (anti) kaon-nucleon scattering. A meson-baryon bound-state picture suggests another type of the multi-quark structure. A spin-3/2 − partner of this resonance, i.e. Λ(1520) (≡ Λ * ) whose mass is similar to that of Θ + but strangeness is opposite is yet another interesting resonance. It can be produced simultaneously in the Θ + photoproduction from the deuteron target. The LEPS collaboration is searching for the Θ + associated with the production of the Λ * in photoproduction off the deuteron [2]. Since the measurement of the Λ * can be performed much more reliably, the detailed understanding of the production mechanism of this resonance would be useful to extract information of the Θ + .As far as the experimental data of the Λ * production are concerned, there are experiments reported so far: Boyarski (photoproduction)et al. [3], the Daresbury group (photoproduction) [4], and the CLAS collaboration (electroproduction) [5]. However, these two production mechanisms showed rather different tendencies: While in Ref.[3] and in the Daresbury experiment K * -exchange is known to be dominant in the t-channel, the CLAS experiment indicates that pseudoscalar K-exchange governs the process. Moreover, the kinematical regions of these experiments are different, so that a mere comparison is not meaningful.In the present work, we investigate the photoproduction of the Λ * near the threshold. Based on the effective Lagrangian for meson-baryon vertices, we use the Born approximation. We introduce form factors at the vertices, which reflect the internal structure of hadrons but bring in model dependence. However, there is a caveat: Introducing the form factors violates the gauge invariance of the electromagnetic interaction, which causes the Ward-Takahashi identity to be broken. Thus, we have to take care of the form factors to restore the gauge invariance. Since there is no unique theoretical way to introduce the g...

Roles of nucleon resonances inΛ(1520) photoproduction off the proton

“…t−channel contact term as shown in the literatures [12,14,18] it is not considered in this work. Besides the Born terms, including s-, K exchanged t-channels and contact term, the contributions from the K * exchanged t-and resonance (R) intermediate s-channels are considered in the current work.…”

“…As discussion in Ref [19], the coupling constant for the Reggeized treatment can be different from the one in the effective Lagrangian approach. Here we do not adopt the value about 1 determined by S U(6) model [20], but the larger one, about 10, by quark model [20] and phenomenological fitting of Nam et al [18] and Totiv et al [21]. The scattering amplitude for the photoproduction can be written as follow:…”

“…(18,21) show both radiative and strong decay of the nucleon resonance with J > 1/2 are described by two coupling constants. In this appendix we will show how to extract coupling constants from the helicity amplitudes and partial decay amplitudes.…”

η-meson photoproduction andN* resonances

“…As indicated in Ref. [16,17], we use the simplified form for the spin-3/2 propagator as given in Eq. (11), since this form dominates the low energy region.…”

“…We utilize the phenomenological form factors in terms of a gauge-invariant manner as done in Ref. [15,16,17]. As a result, we observe that µ γnn * (1675) = 0.1 ∼ 0.2 and µ γpp * (1675) 0 for J P = 1/2 ± whereas µ γnn * (1675) = 0.01 ∼ 0.02 and µ γpp * (1675) 0 for J P = 3/2 ± to reproduce the GRAAL data qualitatively well.…”