New insight into the low-energy ${}^9$He spectrum

Abstract

The spectrum of ${}^9$He was studied by means of the ${}^8$He($d$,$p$)${}^9$He reaction at a lab energy of 25 MeV/n and small center of mass (c.m.) angles. Energy and angular correlations were obtained for the ${}^9$He decay products by complete kinematical reconstruction. The data do not show narrow states at $\sim$1.3 and $\sim$2.4 MeV reported before for ${}^9$He. The lowest resonant state of ${}^9$He is found at about 2 MeV with a width of $\sim$2 MeV and is identified as $1/2^{-}$. The observed angular correlation pattern is uniquely explained by the interference of the $1/2^{-}$ resonance with a virtual state $1/2^{+}$ (limit on the scattering length is obtained as $a>-20$ fm), and with the $5/2^{+}$ resonance at energy $\ge 4.2$ MeV.

5 pages, 4 figures, 2 tables