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HK: Physik der Hadronen und Kerne

HK 15: Theorie II

HK 15.2: Talk

Tuesday, March 20, 2001, 14:30–14:45, B

Pion-Deuteron Dynamics in Effective Field Theory — •Harald W. Grießhammer and Bugra Borasoy — Technische Universität München

The Effective Field Theory of low energy few nucleon systems allows for simple, model independent, systematic and rigorous computations with an error estimate. We here deal with the formulation in which the dynamical pion is included as perturbation, as proposed by Kaplan, Savage and Wise. In this frame, our calculations are the first ones to include pions also in the initial or final state. First, the deuteron pion scattering length is calculated to next-to-leading order, i.e. with an accuracy of about 10%. One two nucleon, two pion contact interaction (counter term) which breaks chiral symmetry, and one which obeys it are encountered at that order. By comparing to the experimental results, we show that the combination of counter terms entering is of the expected, natural size and contributes about 30% of the scattering length. Secondly, we consider photo- and electro-production of neutral pions at rest off the deuteron. Besides the pion electro-production mechanism on one nucleon and by pion re-scattering, we predict that contact interactions between the pion, photon and two nucleons are next-to-leading order, i.e. effects of the order of 30%. These counter terms are fixed using recent MAMI data. We compare our findings to the EFT variant in which pion contributions are iterated.