Neutron correlations in the decay of the first excited state of 11Li

Abstract

The decay of unbound excited 11 Li was measured after being populated by a two-proton removal from a 13 B beam at 71 MeV/nucleon. Decay energy spectra and Jacobi plots were obtained from measurements of the momentum vectors of the 9 Li fragment and neutrons. A resonance at an excitation energy of ∼1.2 MeV was observed. The kinematics of the decay are equally well fit by a simple dineutron-like model or a phase-space model that includes final state interactions. A sequential decay model can be excluded.

First Observation of Unbound O11 , the Mirror of the Halo Nucleus LiWebb1, Wang2, Brown3 et al. 2019Phys. Rev. Lett.445390View full textAdd to dashboardCite

“…Thus we are forced to also include contributions from the two 5/2 + states which would require the two knocked-out neutrons to come from different shells to conserve parity. An analogous state has been observed in the mirror reaction, i.e., in two-proton knockout from 13 B at a similar bombarding energy, the first-excited state of 11 Li was observed [35] which has positive parity [36,37]. This state is consistent with the 5/2 + The Q 2p value for the 3/2 − 1 state is only 1.1σ from the IMME extrapolation [15].…”

First observation of unbound $^{11}$O, the mirror of the halo nucleus $^{11}$Li

“…Thus we are forced to also include contributions from the two 5/2 + states which would require the two knocked-out neutrons to come from different shells to conserve parity. An analogous state has been observed in the mirror reaction, i.e., in two-proton knockout from 13 B at a similar bombarding energy, the first-excited state of 11 Li was observed [34] which has positive parity [35,36]. This state is consistent with the 5/2 + 1 11 Li state obtained in our calculations.…”

Chronology of the three-body dissociation of 8He

“…[27]. This model described accurately the lowenergy peaks observed in the n-n final state of previous works [11,12,13,22,24,25], although contrary to Refs. [26,27] the value of a nn was fixed and it was the size of the source that was varied.…”

“…The origin of the difference in the interpretation of these core-n-n final states and the analogous core-p-p ones is not clear yet. While the microscopic structure of the 2p emitter, a rather narrow state, seems to govern the p-p distributions [4,19,20], the n-n ones appear to be dominated by the effects of the s-wave n-n FSI [11][12][13][22][23][24][25], as if the system went directly into the three-body continuum. In fact, in all the neutron works the systems were populated in a broad continuum of decay energies.…”

“…However, the core-n-n final states measured to date do not exhibit any such patterns. In the 2n decay from the continuum of 5 H [22, 23], 6 He [11,22], 8 He (this work), 11 Li [11,24], 14 Be [11,12], 16 Be [25], 18 C and 20 O [13], the strength is systematically located at low n-n energy, as predicted by [6,7]. This low-energy signal is originated by the s-wave n-n interaction, and is in fact used in the reaction with the simplest two-neutron final state, 2 H(π − ,γ)2n, to determine the n-n scattering length a nn [26,27].…”