Erlangen 2001 – wissenschaftliches Programm

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HK: Physik der Hadronen und Kerne

HK 22: Elektromagnetische und hadronische Proben IV

HK 22.5: Vortrag

Dienstag, 20. März 2001, 17:45–18:00, C

Charged Pion Capture on a Nucleon at Low Energies — •T.R. Hemmert², H.W. Fearing¹, R. Lewis³ und C. Unkmeir⁴ — ¹TRIUMF, Vancouver BC, Canada — ²Physik-Department T39, TU München — ³Physics Dept., U. Regina, Regina SK, Canada — ⁴Inst. f. Kernphysik, Universität Mainz

The differential cross sections for π⁻ p → γ n and π⁺ n → γ p for pion beam energies up to 40 MeV are computed [1] to next-next-to-leading (N²LO) order in heavy baryon chiral perturbation theory (HBChPT). The results at leading and and at next-to-leading order are completely determined by well-known nucleon properties like masses, anomalous magnetic moments, etc.. At N²LO one encounters three unknown parameters—low energy constants of the HBChPT Lagrangian—which are determined by fitting to experimental data [2]. Two acceptable fits are obtained, which can be separated by comparing with dispersion relation calculations [3] of the inverse process, recently measured at SAL [4]. Low energy theorems for the charged pion multipoles are obtained at threshold. For an incoming s-wave pion one of course obtains the well-known physics associated with the Kroll-Ruderman term [5]. In this contribution, however, we want to focus on the effects of the spontaneously broken chiral symmetry of QCD on the less familiar p-wave multipoles, accessible in charged pion capture or charged pion photoproduction on a nucleon.

[1] H.W. Fearing et al., Phys. Rev. C62 (2000) 054006

[2] M. Salomon et al., Nucl. Phys. A414 (1984) 493

[3] O. Hanstein, D. Drechsel and L. Tiator, Phys. Lett. B399 (1997) 13

[4] E. Korkmaz et al., Phys. Rev. Lett. 83 (1999) 3609

[5] e.g. V. Bernard, N. Kaiser and U.-G. Meißner, Phys. Lett. B383, (1996) 116