Abstract
We present a theoretical parametrization of the nucleon electromagnetic form factors (FFs) based on a combination of chiral effective field theory and dispersion analysis. The isovector spectral functions on the two-pion cut are computed using elastic unitarity, chiral pion–nucleon amplitudes, and timelike pion FF data. Higher-mass isovector and isoscalar t-channel states are described by effective poles, whose strength is fixed by sum rules (charges, radii). Excellent agreement with the spacelike proton and neutron FF data is achieved up to Q2∼1 GeV2. Our parametrization provides proper analyticity and theoretical uncertainty estimates and can be used for low-Q2 FF studies and proton radius extraction.
Highlights
The electromagnetic form factors (EM FFs) parametrize the transition matrix element of the EM current between nucleon states and represent basic characteristics of nucleon structure
The FFs at spacelike momentum transfers Q2 1 GeV2 have been measured in a series of elastic electron scattering experiments [1, 2, 3], most recently at the Mainz Microtron (MAMI) [4, 5, 6] and at Jefferson Lab [7, 8, 9]
In recent work we developed a method for computing the spectral functions of nucleon FFs on the two-pion cut using a combination of χEFT and amplitude analysis
Summary
The electromagnetic form factors (EM FFs) parametrize the transition matrix element of the EM current between nucleon states and represent basic characteristics of nucleon structure. In this letter we use DIχEFT to calculate the nucleon FFs up to Q2 ∼ 1 GeV2 (and higher) and construct a dispersive parametrization of the FFs with theoretical uncertainty estimates This is achieved by extending our previous calculations in two aspects: (a) We partially include N2LO chiral loop corrections in the isovector magnetic spectral function, by parametrizing them in a form similar to the N2LO corrections in the electric case. (b) We account for higher-mass t-channel states in the spectral functions (isovector and isoscalar) by parametrizing them through effective poles, whose strength is determined by sum rules (charges, magnetic moments, radii) This allows us to extend the dispersion integrals to higher masses and compute the spacelike FFs up to higher Q2. In the following we describe the calculation and results and discuss potential applications of our FF parametrization
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