Lifetime measurements of excited states in 20O populated by direct nucleon transfer

The oxygen isotopes are a fantastic laboratory for the study of the nuclear force and phenomena when approaching the drip line. Neutron rich Oxygen isotopes have revealed the reduction of the N=20 shell gap and the possible role of the 3-body interaction in the nuclear force. Non-yrast states in even-even isotopes can provide relevant information in the study of realistic interactions in the sd-shells. In particular, the second 2+ and first 3+ states in 20O constructed from a pure neutron excitation (d5/2)3(s1/2)1 is sensitive to the relative position of d5/2 and s1/2 shell which can be influenced by the contribution of the 3-body interaction. Due to this simple configuration, the 2+2 state is strongly populated in the 19O(d,p)20O reaction. Using the selectivity of the VAMOS++ spectrometer, the high intense secondary beam of 19O from SPIRAL1, the accurate excitation energy selection in 20O using the MUGAST array and the high resolution gamma-ray spectrometer AGATA, we propose to perform an accurate measurement of the fs lifetime of the 2+2 and 3+1 states via their gamma decay to the first 2+ state. This experiment will be a pioneer experiment aiming at combining direct reaction with lifetime measurement in the fs range.