Hadronic shift in pionic hydrogen

Elvira²,

Kubis³

et al. 2015

Phys. Rev. Lett.

191

176

We match the results for the subthreshold parameters of pion-nucleon scattering obtained from a solution of Roy-Steiner equations to chiral perturbation theory up to next-to-next-to-next-to-leading order, to extract the pertinent low-energy constants including a comprehensive analysis of systematic uncertainties and correlations. We study the convergence of the chiral series by investigating the chiral expansion of threshold parameters up to the same order and discuss the role of the ∆(1232) resonance in this context. Results for the low-energy constants are also presented in the counting scheme usually applied in chiral nuclear effective field theory, where they serve as crucial input to determine the long-range part of the nucleon-nucleon potential as well as three-nucleon forces.

Section: Introductionmentioning

confidence: 99%

Matching Pion-Nucleon Roy-Steiner Equations to Chiral Perturbation Theory

Elvira²,

Kubis³

et al. 2015

Phys. Rev. Lett.

191

176

“…In addition to the error estimates for the partial waves, we construct a description of the pion vector form factor fit to the latest experimental results from BaBar [47], KLOE [48], and BESIII [49] and consistent with the input for the ππ P -wave phase shifts used in the solution of the RS system. This procedure ensures that the resulting spectral function fulfills all available constraints from modern low-energy data, including the precision measurements of πN dynamics extracted from pionic atoms [50][51][52][53][54]. In addition to their relevance in stabilizing form-factor fits, the resulting spectral functions also find applications in improving the nucleon-pole-term contribution to bremsstrahlung of a ρ in proton-nucleus scattering [55] and in the transverse charge densities of the nucleon [56].…”

Section: Introductionmentioning

confidence: 99%

On the $\pi\pi$ π π continuum in the nucleon form factors and the proton radius puzzle

Kubis²,

Elvira³

et al. 2016

Eur. Phys. J. A

Abstract. We present an improved determination of the ππ continuum contribution to the isovector spectral functions of the nucleon electromagnetic form factors. Our analysis includes the most up-to-date results for the ππ →N N partial waves extracted from Roy-Steiner equations, consistent input for the pion vector form factor, and a thorough discussion of isospin-violating effects and uncertainty estimates. As an application, we consider the ππ contribution to the isovector electric and magnetic radii by means of sum rules, which, in combination with the accurately known neutron electric radius, are found to slightly prefer a small proton charge radius.

“…where the reference valuesā Is refer to the values extracted from high-precision data on pionic atoms taken at PSI [27][28][29], leading to [23,30,31] …”

Section: Introductionmentioning

confidence: 99%

Extracting the σ-term from low-energy pion-nucleon scattering

Elvira

J. Phys. G: Nucl. Part. Phys.

Kubis³

et al. 2017

Abstract. We present an extraction of the pion-nucleon (πN ) scattering lengths from low-energy πN scattering, by fitting a representation based on RoySteiner equations to the low-energy data base. We show that the resulting values confirm the scattering-length determination from pionic atoms, and discuss the stability of the fit results regarding electromagnetic corrections and experimental normalization uncertainties in detail. Our results provide further evidence for a large πN σ-term, σ πN = 58(5) MeV, in agreement with, albeit less precise than, the determination from pionic atoms.