Measurement of the Partial Cross Sections s(TT), s(LT) and [s(T)+epsilon*s(L)] of the p(e,e' pi+)n Reaction in the Delta(1232) Resonance

TL;DR

This paper presents precise measurements of partial cross sections in the p(e,e' pi+)n reaction within the Delta(1232) resonance, providing critical data to test and challenge existing theoretical models at low Q2.

Contribution

It provides the first low-Q2 measurements in the pi+ channel, offering new experimental data to evaluate and refine theoretical descriptions of the resonance.

Findings

Chiral effective field theory does not match the experimental data.

Sato-Lee model calculations are inconsistent with the measurements.

The data reveal non-zero cross sections at the lowest Q2, challenging existing models.

Abstract

We report new precision p(e,e' pi+})n measurements in the Delta(1232) resonance at Q2 = 0.127(GeV/c)2 obtained at the MIT-Bates Out-Of-Plane scattering facility. These are the lowest, but non-zero, Q2 measurements in the pi+ channel. The data offer new tests of the theoretical calculations, particularly of the background amplitude contributions. The chiral effective field theory and Sato-Lee model calculations are not in agreement with this experiment.