Determination of exotic hadron structure by constituent-counting rule for hard exclusive processes

We propose to use hard exclusive production of an exotic hadron for finding its internal quark-gluon configuration by the constituent-counting rule in perturbative QCD. In particular, the cross section for the exclusive process π^-+p→K⁰+Λ(1405) is estimated at the scattering angle θ=90^∘ in the center-of-mass frame by using current experimental data. In comparison, the cross section for the ground-state Λ production π^-+p→K⁰+Λ is also shown. We suggest that the internal quark configuration of Λ(1405) should be determined by the asymptotic scaling behavior of the cross section. If it is an ordinary three-quark baryon, the scaling of the cross section is s⁸dσ/dt=constant, whereas it is s¹⁰dσ/dt=constant if Λ(1405) is a five-quark hadron, where s and t are Mandelstam variables. Such a measurement will be possible, for example, by using the high-momentum beam line at Japan Proton Accelerator Research Complex. In addition, another exclusive process γ+p→K⁺+Λ(1405) could be investigated at laser electron photon beam line at SPring-8 and JLab for finding the nature of Λ(1405). We indicate that the constituent-counting rule could be used as a valuable quantity in determining internal structure of exotic hadrons by high-energy exclusive processes, where quark-gluon degrees of freedom explicitly appear. Furthermore, it is interesting to investigate the transition from hadron degrees of freedom to quark-gluon ones for exclusive exotic-hadron production processes.