Average CsI neutron density distribution from COHERENT data

Abstract

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 $R_n=5.5{}_{-1.1}^{+0.9}\text{fm}$ 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.

Comments: 6 pages. To be published in Physical Review Letters