Neutrino-nucleus elastic scattering ($\nu { \rm A}_{ el}$) provides a unique laboratory to study the quantum-mechanical (QM) coherency effects in electroweak interactions. The deviations of the cross-sections from those of completely coherent systems can be quantitatively characterized through a coherency parameter $\alpha ( q^2 )$. The relations between $\alpha$ and the underlying nuclear physics in terms of nuclear form factors are derived. The dependence of cross-section on $\alpha ( q^2 )$ for the various neutrino sources is presented. The $\alpha ( q^2 )$-values are evaluated from the measured data of the COHERENT CsI and Ar experiments. Complete coherency and decoherency conditions are excluded by the CsI data with $p { =} 0.004$ at $q^2 { =} 3.1 { \times} 10^{ 3} ~ { \rm MeV^2}$ and with $p { =} 0.016$ at $q^2 { =} 2.3 { \times} 10^{ 3} ~ { \rm MeV^2}$, respectively, verifying that both QM superpositions and nuclear many-body effects contribute to $\nu { \rm A}_{ el}$ interactions.
Categories: hep-ex hep-ph nucl-ex