Unbound states of neutron-rich carbon isotopes

We work upon the model of a two-state mixing of states of pure proton and pure neutron
excitation to describe excited 2+ states in carbon isotopes. The first 2+ state of 16C
has been measured in other works showing it is dominated by neutron excitations and was
recently confirmed in a study that has determined the proton amplitude of the first 2+ state
for 16C, 18C and 20C. The aim of this thesis is to identify the mixed-symmetry 2+ state,
which is above the neutron separation energy and therefore unbound. Its observation will
add weight to our simple picture of describing the neutron-rich C isotopic chain, giving us
great insights into the shell evolution towards the neutron dripline at Z=6.
For that purpose, an experiment was carried out at GSI with the R3B/LAND setup in
order to investigate the structure of unbound states of 16C, 18C and 20C for the first time
via quasi-free scattering (p, 2p) reactions from 17N, 19N, and 21N, respectively.
In this work, the results of the invariant-mass spectroscopy of the one neutron evaporation
decay of 16C and 18C are presented, reporting three resonant states located at 5.71(06),
7.83(41) and 9.78(88) MeV for 16C and four unbound states observed at 5.54(10), 7.51(20),
9.83(33) and 12.31(30) MeV for 18C. These unbound states are discussed in comparison with
shell model calculations performed with WBP, WBT and WBT* interactions. Preliminary
exclusive cross sections are also presented for all of these states.