Two-proton decay of12O and its isobaric analog state in12N

Abstract

Following neutron knockout from a 13 O beam, 12 O fragments were created and the three decay products following two-proton decay were detected. A new ground-state mass was determined by the invariant mass method implying a decay kinetic energy of 1.638(24) MeV, and the width was found to be less than 72 keV. The latter is inconsistent with previous measurements with lower experimental resolutions, but consistent with theoretical estimates. The isobaric analog of 12 O in 12 N was produced from proton knockout reactions with the same beam and decayed by twoproton emission to the isobaric analog state in 10 B with a decay kinetic energy of 1.165(29) MeV. It represents only the second case of an analog state where two-proton decay is the only isospin and energy conserving particle decay mode. With our measurements of the mass excesses of 12 O and it analog, the quadratic form of the isobaric multiplet mass equation was found to fit the A=12 quintet and any deviations are less than the magnitude found for the A=8 quintet and A=7 and 9 quartets.

Second0+state of unboundO12: Scaling of mirror asymmetry

“…We adopted a conservative systematic error for given its strong variation. The deduced E x is consistent with our previous value of 1.8(4) MeV [37,38], but lower than 1.986 (52) MeV reported in the recent study of the 1n knockout reaction at Texas A&M [39]. The difference is visualized in the insets of Figs.…”

“…In Ref. [39], the question as to whether their resonance is a singlet or a doublet is left open due to statistical uncertainties. As one possible scenario, two different states are observed in the present and knockout [39] experiments.…”

“…[39], the question as to whether their resonance is a singlet or a doublet is left open due to statistical uncertainties. As one possible scenario, two different states are observed in the present and knockout [39] experiments. The relative weight of the 0 + state and an unidentified 2 + state would differ in the knockout reaction due to reaction mechanisms and/or acceptance, resulting in energy shift.…”

Strong Neutron Pairing in core+4n Nuclei

“…The analysis of triple fragment-n-n correlations shows that the decay 19 Nð−1pÞ 18 C Ã → 16 C þ n þ n is clearly dominated by direct pair emission. The two-neutron correlation strength, the largest ever observed, suggests the predominance of a 14 C core surrounded by four valence neutrons arranged in strongly correlated pairs.…”

“…Experimental setup.-A stable beam of 40 Ar, accelerated at the GSI facility at 490 MeV=nucleon, was sent on a 4 g=cm 2 Be target to induce fragmentation reactions, in which the 19 …”