Polarizabilities of the nucleon and spin dependent photo-absorption

Abstract

The polarizabilities $\alpha$ (electric), $\beta$ (magnetic) and $\gamma_\pi$ (backward spin) of the nucleon are investigated in terms of degrees of freedom of the nucleon using recent results for the CGLN amplitudes and resonance couplings $A_{1/2}$ and $A_{3/2}$. The photon excitation strengths of the excited states are given in terms of partial integrated photoabsorption cross sections and resonant contributions of the Gerasimov-Drell-Hearn (GDH) sum rule. As a test of the present predictions, cross section differences $(\sigma_{3/2}-\sigma_{1/2})$ of the excited states are compared with data recently measured at MAMI (Mainz) and ELSA (Bonn), In order to explain differences between proton and neutron, radiative widths of the excited states are compared with nonrelativistic and relativistic predictions based on the SU(6) harmonic oscillator (HO) quark model, A complete list of partial contributions from the s-channel and the $t$-channel are given for the polarizabilities

Observation of the Higgs Boson of strong interaction via Compton scattering by the nucleon

“…The present work is a continuation of a systematic series of studies [9,10,[19][20][21][22] on the electromagnetic structure of the nucleon, following experimental work on Compton scattering and a comprehensive review on this topic [23]. These recent investigations have shown [9,10,[19][20][21][22] that a systematic study of all partial resonant and nonresonant photoexcitation processes of the nucleon and of their relevance for the fundamental structure constants of the nucleon as there are the electric polarizability (α), the magnetic polarizability (β) and the backward spin-polarizability (γ π ) is essential for an understanding of the electromagnetic structure of the nucleon.…”

“…The third variable u is not taken into account because of the constraint given in (22). The degrees of freedom of the nucleon including the structure of the constituent quarks enter into the invariant amplitudes via a cut on the real axis of the complex s-plane and in terms of pointlike singularities on the positive real axis of the tplane.…”

“…(a) to (d), have to be supplemented by crossed graphs which are not shown here. Graph (f) is of special interest because it represents the scalar t-channel The main difference between the spin independent cross section (left panel) and the spin dependent cross section (right panel) is the enhancement of the P 33 (1232) contribution by a factor 1.26 which can be traced back to the E2/M1 ratio of the P 33 (1232) resonance [22]. Without the multipolarity mixing the two resonance curves would be the same for the P 33 (1232) resonance.…”

“…The polarizabilities of the nucleon have been measured with high precision and compared with predictions from dispersion theory in several investigations. The most recent one is published in [22]. Therefore, it is not necessary to give an extensive coverage of the polarizabilities here but it is sufficient to present the essential results.…”

“…These recent investigations have shown [9,10,[19][20][21][22] that a systematic study of all partial resonant and nonresonant photoexcitation processes of the nucleon and of their relevance for the fundamental structure constants of the nucleon as there are the electric polarizability (α), the magnetic polarizability (β) and the backward spin-polarizability (γ π ) is essential for an understanding of the electromagnetic structure of the nucleon. In addition it has been found that the structure of the constituent quarks and their coupling to pseudoscalar and scalar mesons is important for the understanding of the electric and magnetic polarizabilities and of the backward spin-polarizability.…”