Hadron Structure in the Non-Perturbative Regime of QCD: Isospin Symmetry and its Violation

Abstract

I discuss recent progress made in calculating electromagnetic corrections in the framework of the effective field theory of QCD. In the case of elastic pion-pion scattering, strong interaction predictions have been worked out to two loop accuracy. I present first results for the electromagnetic corrections in the case of neutral pions. Here, the only sizeable effect comes from the charged to neutral pion mass difference. In the presence of nucleons, isospin violation can be measured in threshold pion photoproduction. I review the present status of the theoretical predictions and the experimental data. I argue that a deeper understanding of isospin violation based on a more precise study of such reactions can be achieved.

10 pp, LaTeX file, 3 figures, uses espcrc1.sty and epsf, plenary talk, QULEN '97, Osaka, May 1997, to be published in the proceedings

References in corpus (2)

• Neutral pion photoproduction on deuterium in baryon chiral perturbation theory to order q^4
• A dispersion theoretical approach to the threshold amplitudes of pion photoproduction

Cited by in corpus (8)

• Chiral perturbation theory
• Observation of a cusp-like structure in the pizero-pizero invariant mass distribution from K+- ==> pi+- pizero pizero decay and determination of the pi-pi scattering lengths
• Interpretation of structure in the di-$J/\psi$ spectrum
• Effects of S-wave thresholds
• Electromagnetic corrections in eta --> 3 pi decays
• Measurement of the Slope Parameter $\alpha$ for the $\eta \to 3{\pi }^0$ decay with the Crystal Ball detector at the Mainz Microtron (MAMI-C)
• Determination of the Dalitz plot parameter alpha for the decay eta->3pi^0 with the Crystal Ball at MAMI-B
• On the size of isospin violation in low-energy pion-nucleon scattering