Q2-Dependence of the Drell-Hearn-Gerasimov integral
1 Kernfysisch Versneller Instituut, Zernikelaan 25, 9747 AA Groningen, The Netherlands
2 Department of Subatomic and Radiation Physics, University of Gent, Proeftuinstraat 86, 9000 Gent, Belgium
Received: 4 May 1999 Communicated by B. Povh
The energy and four-momentum (Q2) dependence of the photo-absorption cross section on the proton is calculated for helicity - and - states. An effective Lagrangian model is used, formulated in terms of meson and baryon degrees of freedom, which obeys crossing symmetry, unitarity, Lorentz and gauge invariance. The difference in the cross sections for the two helicity states, the Drell-Hearn-Gerasimov integral IDHG(Q2), is evaluated at different Q2. We find that at small momentum transfer the absolute value of IDHG(Q2)first increases to reach a maximum at GeV2 before decreasing at higher Q2.
13.40.-f Electromagnetic processes and properties - 13.60.Hb Total and inclusive cross sections (including deep-inelastic processes) - 13.60.Le Meson production - 25.20.Lj Photoproduction reactions - 25.30.-c Lepton-induced reactions