Probing Neutron Skins with KDAR Neutrinos: From Coherent to Diffractive Elastic Neutrino--Nucleus Scattering
Kyoungsu Heo🇰🇷 · Heesung Kwon🇰🇷 · Jaewon Kim🇰🇷 · Jubin Park🇰🇷 · Myung-Ki Cheoun🇰🇷 · Eunja Ha🇰🇷 · Kyung Kwang Joo🇰🇷
We investigate coherent elastic neutrino--nucleus scattering (CENS) induced by pion--decay--at--rest (DAR) and kaon--decay--at--rest (KDAR) neutrinos, with emphasis on the transition from strict coherence to the diffractive regime. Organizing CENS observables in terms of the dimensionless variable , we show that DAR measurements remain confined to the near--coherent region for all nuclei, whereas KDAR neutrinos (~MeV) extend the kinematics into , where recoil spectra develop genuine shape sensitivity to the nuclear weak form factor. Using representative light, medium--mass, and heavy nuclei (C, Ca, Ca, and Pb), we examine relevant cross sections and quantify the statistical sensitivity to the neutron skin thickness achievable at a JSNS--like facility. For a total exposure of 10~tonyear and realistic KDAR fluences, projected sensitivities reach --~fm for Ca and --~fm for Pb as the fluence increases. These sensitivities are competitive with, and complementary to, parity--violating electron--scattering measurements such as CREX and PREX, while relying on an electroweakly clean neutral--current probe with distinct systematic uncertainties. Our results establish KDAR--based CENS as a quantitatively robust and complementary avenue for probing neutron skins and nuclear weak densities beyond the coherent limit.