Abstract
Abstract The structure of the second 2 + resonance in 6 Li is investigated with special emphasis on its isospin 0 components. The wave functions are computed in a three-body model ( α + n + p ) using the hyperspherical adiabatic expansion method combined with complex scaling. In the decay into three free particles the symmetry conserving short-range interaction dominates at short distance whereas the symmetry breaking Coulomb interaction dominates at intermediate and large distances resulting in substantial isospin mixing. We predict the mixing and the energy distributions of the fragments after decay. Computations are consistent with available experiments. We conjecture that nuclear three-body decays frequently produce such large isospin mixing at large distance where the energy distributions are determined.
Highlights
The spatial extension of halo states depends sensitively on their binding energy [1]
For ordinary states the isospin mixing has been established to be in the range 10−4 –10−5 [2]
Reasonable agreement between measurements and simple model calculations can only be obtained with inclusion of both spin zero neutron–proton s-wave (2 H∗ ) and nucleon-α relative d-waves. Some of these authors [8] suggest the large isospin mixture to be due to direct reactions bypassing the 6 Li resonance, whereas others [9] call for better methods for including the Coulomb interaction in three-body calculations
Summary
The spatial extension of halo states depends sensitively on their binding energy [1]. Due to the effect of the Coulomb interaction, the structure of isobaric analog resonances can be very different This influence can be reflected in mixing of different isospin components. Reasonable agreement between measurements and simple model calculations can only be obtained with inclusion of both spin zero neutron–proton s-wave (2 H∗ ) and nucleon-α relative d-waves Some of these authors [8] suggest the large isospin mixture to be due to direct reactions bypassing the 6 Li resonance, whereas others [9] call for better methods for including the Coulomb interaction in three-body calculations. The dominant isospin 1 wave function at small distance can decay into continuum final states with isospin 0 provided the coupling is sufficiently strong This is most likely at distances just outside the ranges of the short-range interactions where the Coulomb interaction still is substantial and completely dominating.
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