Abstract. Alpha-nucleon scattering in the GeV region is discussed in the framework of the folding model. The example of a-scattering from IH and 4He shows that for small momentum transfers a consistent description of elastic and inelastic scattering is obtained which may allow to extract quantitative information on scalar properties of baryons. 25.55.Ci; 14.20.Gk; 25.10.+S
PACS:The detailed experimental study of the properties of baryons is of large importance for the understanding of the features of the strong interaction at low energy. The investigation of baryons in the ground state and in the resonance region is possible with leptonic and hadronic probes. It is obvious that spin-isospin properties of baryon resonances can well be investigated in reactions with real and virtual photons. However, these probes present vector fields in which basic properties of baryons, like the scalar structure related to the coupling of scalar mesons, cannot be studied. Only by the time component of the electromagnetic field, the longitudinal part of virtual photon scattering, aspects of the charge distribution can be investigated. For a more general study of the scalar structure, one would like to have a rather pure scalar hadronic probe which may be provided by complex baryons like a-particles.The scattering problem of composite particles, in particular a-scattering in the GeV region, has been studied in many different approaches [1 8]. In this letter we concentrate on the discussion of a-scattering at small momentum transfer in a single scattering approximation within the framework of the folding model [9]. The advantage of this model is the consistent description of elastic and inelastic processes -using an optical potential and the distorted wave born approximation. Further, this formalism was very successfully applied to many problems in nuclear physics and allows to extract spectroscopic information on ground state and transition properties [10].Using a description of the a-scattering problem within the frame of the relativistic Schr6dinger equation the Hamilton operator contains an optical potential of the following form:
Vopt (R) = Vcom (R) --(Vo + i Wo) F (R) +( h 12(VI~+iWjF,(R)s.I. \m~ c/(1) Vo, W0, Vts and Wl, are the potential amplitudes for the real and imaginary potential part of the baryon central and spin-orbit potential, respectively, and Vco.1 represents the Coulomb potential. R is the distance between the target and projectile center of mass. The imaginary potential takes into account the effect of absorption. Although the strength of the effective interaction V 0 can be estimated in certain models, e.g. in meson exchange models, the complex amplitude Vo + i Wo is in general adjusted to the cross section of elastic scattering. The radial form of the potential F(R) is given by the folding integralwhere pl(r) and p2(r') present ground state densities of target and projectile, which are connected by an effective baryon-baryon interaction g(R + r-r') between the constituents of target and projectile. In the fol...
