Measurement of the N to Delta(1232) Transition at High Momentum Transfer by pi0 Electroproduction

TL;DR

This study measures the N to Delta(1232) transition via pi0 electroproduction at high Q2, revealing how the transition form factors evolve from non-perturbative to perturbative regimes.

Contribution

It provides the highest Q2 data for the N to Delta transition, showing the Q2 dependence of multipole ratios and form factors with unprecedented precision.

Findings

G*M decreases more steeply than proton magnetic form factor

E1+/M1+ ratio is small and negative, indicating helicity non-conservation

S1+/M1+ ratio is negative and increases in magnitude with Q2

Abstract

We report a new measurement of the exclusive electroproduction reaction gamma* p -> pi0 p to explore the evolution from soft non-perturbative physics to hard processes via the Q2 dependence of the magnetic (M1+), electric (E1+) and scalar (S1+) multipoles in the N to Delta transition. 9000 differential cross section data points cover W from threshold to 1.4 eV/c2, 4pi center-of-mass solid angle, and Q2 from 3 to 6 GeV2/c2, the highest yet achieved. It is found that the magnetic form factor G*M decreases with Q2 more steeply than the proton magnetic form factor, the ratio E1+/M1+ is small and negative, indicating strong helicity non-conservation, and the ratio S1+/M1+ is negative, while its magnitude increases with Q2.