In-beam γ -ray spectroscopy toward the proton dripline: The curious case of Ar 32

High-resolution in-beam γ-ray spectroscopy was used to study excited states of the neutron-deficient nucleus Ar32 populated in fast-beam induced four- and six-nucleon removal reactions from Ca36,38. One new γ-ray transition and indications for an additional two were found, allowing for a glimpse at the level scheme beyond the 21+ state. The nature of the new 1900(4)-keV transition is discussed in the context of the known energy spectrum of the mirror nucleus Si32 and shell-model calculations using the FSU and SDPF-M cross-shell effective interactions. Its resulting parent state at 3767(5)keV, more than 1.3 MeV above the proton separation energy, is tentatively assigned to have mixed sd-shell and 2p-2h character. It might either be the mirror of the Jπ=22+ state of Si32 at 4230.8(8)keV, but with a decay branch favoring a transition to the 21+ over the ground state, or the mirror of the 4983.9(11)-keV state with quantum numbers 0+. The resulting mirror-energy differences of -473(5) and -1218(5)keV are both sizable when compared to systematics; in the latter case the result would, in fact, be among the largest reported to date in the nuclear chart or suggest the potential existence of an additional, hitherto unidentified, low-lying 0+ state of Si32.