= Spin-independent WIMP-nucleus scattering
{title2=$\sigma_A(0)=\sigma_p(\mu_A/\mu_p)^2A^2$ for equal proton/neutron couplings}
An elastic recoil interaction whose leading coherent nuclear amplitude does not depend on nuclear spin. At low <momentum> transfer, <proton> and neutron amplitudes add; equal couplings give an $A$-fold amplitude and the displayed cross-section scaling, with reduced <masses> $\mu_A$ and $\mu_p$. A finite-momentum nuclear form factor reduces coherence. Unequal <nucleon> couplings or other interactions change how experiments on different targets should be compared.
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