Using the coherent elastic neutrino-nucleus scattering data of the COHERENT experiment, we determine for the first time the average neutron rms radius of $^{ 133}\text{ Cs}$ and $^{ 127}\text{ I}$. We obtain the practically model-independent value $ R_{ n} = 5.5 { }^{ +0.9}_{ -1.1} \, \text{ fm} $ using the symmetrized Fermi and Helm form factors. We also point out that the COHERENT data show a $2.3\sigma$ evidence of the nuclear structure suppression of the full coherence.
Categories: hep-ph hep-ex nucl-ex nucl-th