Data from AR_93034_5.ens

The stability of the first excited state of ⁸Li against decay into decay into ⁴He+⁴h (1988Aj01) sets an upper limit for B(⁴h)≤3.53 MeV (see refs in 1992Ti02). This also sets a lower limit to the β^- decay energy ⁴h-->⁴He of 17.06 MeV. The upper limit of the β^- decay energy would be 20.06 MeV, if ⁴h is stable against decay into ³h+n. Estimates for the expected half-life of the β decay: if J^π(⁴h)=0-, 1-, 2-, T_½≥10 min; if J^π (⁴h)=0+, 1+, T_½≥0.03 s (see discussion in 1992Ti02). Experimentally there is no evidence for any β^- decay of ⁴H, nor has particle stable ⁴h been observed. Evidence for a particle-unstable state of ⁴h has been obtained in ⁷Li(π^-,t)³h+n at 8 MeV 3 above the unbound ³h+n mass with a width of 4 MeV. For other theoretical work see (1976Ja24, 1983Va31, 1985Ba39, 1988Go27).

The level structure presented here is obtained from a charge-symmetric reflection of the R-matrix parameters for ⁴Li after shifting all the p-³He E(λ) values by the internal Coulomb energy difference ΔE(Coulomb)=-0.86 MeV. The parameters then account well for measurements of the n-³h total cross section (1980Ph01) and coherent scattering length (1985Ra32), as is reported in (1990Ha23). The Breit-Wigner resonance parameters from that analysis for channel radius a(n-t)=4.9 fm are given. The levels are located substantially lower in energy than they were in the previous compilation (1973Fi04), as will be true for all the T=1 levels of the A=4 system. The ⁴Li analysis unambiguously determined the lower 1- level to be predominantly ³p₁ and the upper one to be mainly ¹p₁; that order is preserved, of course, in the ⁴h levels. In addition to the given levels, the analysis predicts very broad positive-parity states at excitation energies in the range 14-22 MeV, having widths much greater than the excitation energy, as well as antibound p-wave states approximately 13 MeV below the 2- ground state. Parameters were not given for these states because there is no clear evidence for them in the data.

The structure given by the s-matrix poles is quite different, however. The p-wave resonances occur in a different order, and the positive-parity levels (especially for 0+ and 1+) are much narrower and lower in energy. It is possible that these differences in the s-matrix and K(R)-matrix pole structures, which are not yet fully understood, could explain the puzzling differences that occur when these resonances are observed in the spectra of multi-body final states.