Pionic hydrogen and deuterium

Detlev Gotta,L M Simons

doi:10.21468/scipostphysproc.5.014

Abstract

The measurement of strong-interaction shift and broadening in pionic hydrogen and deuterium yields pion-nucleon scattering lengths as well as the threshold pion-production strength on isoscalar NN pairs. Results from recent high-resolution experiments at PSI using crystal spectrometers allow important comparisons with the outcome of the modern low-energy description of QCD within the framework of effective field theories.

Highlights

The last decades have seen a successful theoretical description of strong-interaction phenomena at threshold within effective field-theory (EFT) approaches: the chiral symmetry of the QCD Lagrangian allows the derivation of so-called low-energy theorems
The unknown structure of QCD at short distances is parametrized by so-called lowenergy constants (LECs), which must be taken from experiment as long as results from latticeQCD calculations are not available
Exotic atoms provide an ideal laboratory for the extraction of scattering lengths from experiment, because problems due to normalization and extrapolation to threshold inherent to scattering experiments are absent

Summary

14.1 Introduction

The last decades have seen a successful theoretical description of strong-interaction phenomena at threshold within effective field-theory (EFT) approaches: the chiral symmetry of the QCD Lagrangian allows the derivation of so-called low-energy theorems. The chiral symmetry is explicitly broken because of the finite masses of the light quarks u, d, and s. A chiral expansion, ordered by the powers of (small) momenta, the quarkmass differences, and the fine structure constant α, includes strong isospin-breaking effects resulting from the quark-mass differences and those of electromagnetic origin on the same footing. ΠN → πN reactions and the corresponding scattering lengths are of fundamental interest for the understanding of low-energy QCD phenomena. Properties of exotic atoms and experimental methods are outlined in [3]

14.2 Strong-interaction effects

14.3 Experimental approach

14.4 Results

14.5 Summary