Das Nukleon im modifizierten harten Streubild

Exclusive reactions involving nucleons are studied within the modified hard scattering picture which incorporates the transverse hadronic structure and gluonic radiative corrections in form of a Sudakov factor. Compared to conventional factorization which takes into account only longitudinal degrees of freedom and fails when gluon momenta become soft, the modified approach offers a framework to isolate the genuinely perturbative contribution to exclusive observables. This is achieved by introducing a finite transverse hadronic size which provides a natural infrared (IR) cutoff and thus guarantees the self-consistency of the calculation. In the case of the nucleon the proper choice of the IR-scale requires some care because of the existence of at least three distance scales. The formalism is applied to the magnetic nucleon form factor in the space- and timelike region and to the decay of J/#psi# into N anti N. Whereas the latter reaction is shown to be well explained within the modified hard scattering picture, the perturbative contribution to the form factors is found to fall short by orders of magnitude compared to experimental data. At least for the spacelike case a possible source of this discrepancy can be traced to the large Feynman contribution to such processes which is left out in a perturbative treatment. (orig.)SIGLEAvailable from TIB Hannover: RO 9740(95-10) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman