Pion-less Effective Field Theory on Low-Energy Deuteron Electro-Disintegration

TL;DR

This paper applies low-energy pion-less effective field theory to study deuteron electro-disintegration, achieving good agreement with potential models and data for most observables, but highlighting unresolved discrepancies in the longitudinal-transverse interference cross-section.

Contribution

It demonstrates the effectiveness of pion-less EFT at N2LO and NLO for describing deuteron electro-disintegration near threshold without free parameters, and discusses the limitations in explaining certain experimental discrepancies.

Findings

Good agreement with potential models for L+T, TT, and overall cross-sections.

Discrepancy of up to 30% in  in  between theory and experiment.

Unexplained differences suggest limitations of current theoretical approaches.

Abstract

In view of its relation to Big-Bang Nucleo-Synthesis and a reported discrepancy between nuclear models and data taken at S-DALINAC, electro-induced deuteron break-up 2H(e,e' p)n is studied at momentum transfer q<100MeV and close to threshold in the low-energy nuclear Effective Field Theory without dynamical pions. The result at N2LO for electric dipole currents and at NLO for magnetic ones converges order-by-order better than quantitatively predicted and contains no free parameter. It is at this order determined by simple, well-known observables. Decomposing the doubly differential cross-section into the longitudinal-plus-transverse (L+T), transverse-transverse (TT) and longitudinal-transverse interference (LT) terms, we find excellent agreement with a potential-model calculation by Arenh"ovel et al using the Bonn potential. Theory and data also agree well on \sigma_{L+T}. There is however no space on the theory-side for the discrepancy of up to 30%, 3-\sigma between theory and experiment in \sigma_{LT}. From universality, we conclude that no theoretical approach with the correct deuteron asymptotic wave-function can explain the data. Un-determined short-distance contributions that could affect \sigma_{LT} enter only at high orders, i.e. at the few-percent level. We notice some issues with the kinematics and normalisation of the data reported.