First Measurement of Parity-Nonconserving Neutron-Spin Rotation: The Tin Isotopes

Abstract

A parity-nonconserving (PNC) neutron-spin rotation, ${\ensuremath{\phi}}_{\mathrm{PNC}}$, for neutrons passing through matter due, presumably, to the weak interaction is observed for the first time. For tin isotopes, the following values for ${\ensuremath{\phi}}_{\mathrm{PNC}}$ in ${10}^{\ensuremath{-}6}$ rad/cm are found: $^{124}\mathrm{Sn}$, +0.48\ifmmode\pm\else\textpm\fi{}1.49; $^{117}\mathrm{Sn}$, +36.7\ifmmode\pm\else\textpm\fi{}2.7; and natural Sn, +4.95\ifmmode\pm\else\textpm\fi{}0.93, with the positive sign corresponding to a right-handed rotation about the momentum. Evidence in $^{117}\mathrm{Sn}$ for a larger total cross section for positive-helicity neutrons than for negative-helicity ones is also reported.