Eur. Phys. J. A (2007) 31: 327-333
https://doi.org/10.1140/epja/i2006-10235-1

Regular Article - Hadron Physics

Electromagnetic polarizabilities and the excited states of the nucleon

Zweites Physikalisches Institut der Universität Göttingen, Friedrich-Hund-Platz 1, D-37077, Göttingen, Germany

^* e-mail: mschuma3@gwdg.de

Received: 30 November 2006
Accepted: 9 February 2007
Published online: 29 March 2007

Abstract

The electromagnetic polarizabilities of the nucleon are shown to be essentially composed of the nonresonant α _p(E ₀₊) = + 3.2, α _n(E ₀₊) = + 4.1, the t-channel α ^t _{p, n} = - β ^t _{p, n} = + 7.6 and the resonant β _{p, n}(P ₃₃(1232)) = + 8.3 contributions (in units of 10^-4fm^3). The remaining deviations from the experimental data Δα _p = 1.2±0.6, Δβ _p = 1.2±0.6, Δα _n = 0.8±1.7 and Δβ _n = 2.0±1.8 are contributed by a larger number of resonant and nonresonant processes with cancellations between the contributions. This result confirms that dominant contributions to the electric and magnetic polarizabilities may be represented in terms of two-photon coupling to the σ-meson having the predicted mass m _σ = 666MeV and two-photon width Γ _γγ = 2.6keV.