Novel Measurement of the Neutron Magnetic Form Factor from $\mathrm{A}=3$ Mirror Nuclei

The electromagnetic form factors of the proton and neutron encode information on the spatial structure of their charge and magnetization distributions. While measurements of the proton are relatively straightforward, the lack of a free neutron target makes measurements of the neutron’s electromagnetic structure more challenging and more sensitive to experimental or model-dependent uncertainties. Various experiments have attempted to extract the neutron form factors from scattering from the neutron in deuterium, with different techniques providing different, and sometimes large, systematic uncertainties. We present results from a novel measurement of the neutron magnetic form factor using quasielastic scattering from the mirror nuclei ${}^3\mathrm{H}$ and ${}^3\mathrm{He}$, where the nuclear effects are larger than for deuterium but expected to largely cancel in the cross-section ratios. We extracted values of the neutron magnetic form factor for low-to-modest momentum transfer, $0.6<Q^2<2.9{\mathrm{GeV}}^2$, where existing measurements give inconsistent results. The precision and $Q^2$ range of these data allow for a better understanding of the current world’s data and suggest a path toward further improvement of our overall understanding of the neutron’s magnetic form factor.

Figure 1

Previous $G_M^n$ extractions [8, 9, 10, 13, 14, 15, 16, 17], uncertainties include statistical and uncorrelated systematics, while the Lachniet result includes a band representing their correlated systematic uncertainty. The plot also shows a recent fit (Ye) of world’s data [18], plus curves for the hypercentral (De Sanctis) constituent quark model [19] and a dispersion-theoretical analysis (Hammer) from Ref. [20].

Figure 2

Cross sections and statistical uncertainties for ${}^3\mathrm{H}$ and ${}^3\mathrm{He}$ compared to short-time approximation calculations of Ref. [32] for the L24 ($0.703{\mathrm{GeV}}^2$) and R24 ($2.313{\mathrm{GeV}}^2$) settings. The black (gray) points are the measured total cross section, and the red (orange) points are after subtraction of the inelastic contribution. The vertical lines represent $\pm 1\sigma$ from the QE peak (see text for details).

Figure 3

Our new $G_M^n$ results along with a subset of previous measurements [14, 15, 16, 17] (see text for details).