Energy separation of the 1+/1− parity doublet in 20Ne

The parity doublet of 1+/1− states of Ne-20 at 11.26 MeV excitation energy is one of the best known test cases to study the weak part of the nuclear Hamiltonian. The feasibility of parity violation experiments depend on the effective nuclear enhancement factor (RN/|E(1+) − E(l−)|) which amplifies the impact of the matrix element of the weak interaction on observables indicating parity mixing. An extreme large value of Rn/|E(1+) − E(l−)| = (670 ± 7000) MeV−1 was reported for the doublet in 20Ne. The large uncertainty depends amongst others on the large uncertainty of |E(1+) − E(l−)| = 7.7±5.5 keV of the parity doublet. Nuclear resonance fluorescence (NRF) experiments with linearly and circularly polarized photon beams were performed at the High Intensity Gamma-Ray Source at Duke University, Durham, NC, USA, to determine the energy difference of the parity doublet with higher precision. The different angular distributions for 0+ → 1− → 0+ and 0+ → 1+ → 0+ NRF cascades in polarized γ-ray beams were used to determine the energy difference of the parity doublet to 2.9(13) keV.