The ratio of proton's electric to magnetic form factors measured by polarization transfer

TL;DR

This paper measures the ratio of proton's electric to magnetic form factors using polarization transfer, revealing a decreasing trend with increasing momentum transfer and indicating different spatial distributions of charge and magnetization.

Contribution

It provides the first detailed polarization transfer measurements of the form factor ratio over a range of momentum transfers, improving understanding of proton structure.

Findings

The ratio decreases with increasing momentum transfer.

Charge and magnetization distributions in the proton differ.

Systematic uncertainties were well controlled.

Abstract

The ratio of the proton's elastic electromagnetic form factors was obtained by measuring the transverse and longitudinal polarizations of recoiling protons from the elastic scattering of polarized electrons with unpolarized protons. The ratio of the electric to magnetic form factor is proportional to the ratio of the transverse to longitudinal recoil polarizations. The ratio was measured over a range of four-momentum transfer squared between 0.5 and 3.5 GeV-squared. Simultaneous measurement of transverse and longitudinal polarizations in a polarimeter provides good control of the systematic uncertainty. The results for the ratio of the proton's electric to magnetic form factors show a systematic decrease with increasing four momentum squared, indicating for the first time a marked difference in the spatial distribution of charge and magnetization currents in the proton.