Erlangen 2001 – wissenschaftliches Programm

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HK: Physik der Hadronen und Kerne

HK 10: Postersitzung: Theorie

HK 10.7: Poster

Dienstag, 20. März 2001, 10:30–12:45, R

Pion Charge Radius from Charged Pion Electroproduction — •Veronique Bernard¹, Norbert Kaiser² und Ulf-G. Meißner³ — ¹Laboratoire de Physique Theorique, Universite Louis Pasteur, Strasbourg — ²Physik-Department, Technische Universität München — ³Institut für Kernphysik (Theorie), Forschungszentrum Jülich

We analyze a low-energy theorem for threshold pion electroproduction which allows one the extract the charge radius of the pion [1]. We show that at the same order where the pion radius enters, pion loops induce a correction to the momentum dependence of the longitudinal dipole amplitude L₀₊⁽⁻⁾. This model-independent correction amounts to an increase of the pion charge radius squared from the electroproduction data, r_π² → r_π² = r_π² +(3/32 f_π²)(16/π²−1), by about 0.26 fm². This sheds light on the apparent discrepancy between the recent determination of the pion radius from π⁺-electroproduction [2] and the one based on elastic pion-electron scattering.

[1] V. Bernard, N, Kaiser, Ulf-G. Meißner, Phys.Rev.C62 028201 (2000).

[2] A. Liesenfeld et al., Phys. Lett. B468, 20 (1999). Supported in part by BMBF and DFG