Dresden 2000 – scientific programme

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HK: Physik der Hadronen und Kerne

HK 2: Theorie I

HK 2.1: Talk

Monday, March 20, 2000, 14:15–14:30, B 81

Compton scattering off the nucleon and polarizabilities — •Barbara Pasquini, Dieter Drechsel, Michael Gorchtein und Marc Vanderhaeghen — Institut für Kernphysik, Universität Mainz, J.-J.-Becher Weg 45, D-55090 Mainz

We present a formalism of fixed-t subtracted dispersion relations for Compton scattering off the nucleon at energies E_γ≤ 500 MeV [1]. The Compton scattering amplitude is calculated in terms of subtracted integrals in the s-channel, which are well saturated by one-pion photoproduction multipoles, and t-dependent subtraction functions. These subtraction functions contain a first contribution from subtracted dispersion integrals in the t-channel which are evaluated using the contribution from ππ intermediate states along the positive-t cut and the s- and u- channel Δ(1232) and non-resonant π N exchange along the negative-t cut. A second contribution comes from subtraction constants which are directly related to the scalar polarizabilities, α and β, and the third order spin polarizabilities, γ_i. As a result, these low energy structure constants enter as free parameters which are extracted via a fit to recent Compton scattering data. We also discuss higher order polarizabilities of the nucleon which can be reasonably evaluated by means of the subtracted dispersion relations, comparing the dispersion results with predictions from heavy baryon chiral perturbation theory [2].

[1] D. Drechsel, M. Gorchtein, B. Pasquini, and M. Vanderhaeghen, hep-ph/9904290; Phys. Rev. C in press.

[2] B.R. Holstein, D. Drechsel, B. Pasquini, and M. Vanderhaeghen, hep-ph/9910427; submitted to Phys. Rev. D