2020/01/12 by Dmitrij Siemens, Siemens, Dmitrij · 2 citations
Physics and Astronomy · Chemistry · #Quantum Chromodynamics and Particle Interactions #Particle physics theoretical and experimental studies #Advanced NMR Techniques and Applications
paper · pdf · doi:10.48550/arxiv.2001.03906
For the first time, elastic pion-nucleon scattering is analyzed in the framework of chiral perturbation theory up to fourth order with explicit Δ degrees of freedom. The analysis is performed within the heavy-baryon expansion as well as in a covariant approach based on an extended on-mass-shell renormalization scheme. The renormalization of low-energy constants in both chiral approaches is discussed in detail and the explicit expressions to cancel both power-counting breaking as well as decoupling breaking terms are given. The low-energy constants from the 2πNN interaction as well as additional constants from the Δ sector are reliably constrained by fits to experimental data. The traditional K-matrix unitarization is employed in the near threshold region, whereas a complex mass approach is used to extend the applicability of the theory up to the Δ pole region. Additionally, we estimate a theoretical error based on the truncation of the chiral series as employed in recent analyses of nuclear forces as well as pion-nucleon scattering. The obtained results provide a clear evidence that the explicit inclusion of Δ degrees of freedom is fundamental to describe pion-nucleon physics at threshold. The resulting predictions for the subthreshold and threshold parameters as well as phase shifts are in excellent agreement with the ones determined by the recent Roy-Steiner analysis of pion-nucleon scattering.