A two-neutron halo is unveiled in $^{29}$F

Authors :: Bagchi, S.
Kanungo, R.
Tanaka, Y. K.
Geissel, H.
Doornenbal, P.
Horiuchi, W.
Hagen, G.
Suzuki, T.
Tsunoda, N.
Ahn, D. S.
Baba, H.
Behr, K.
Browne, F.
Chen, S.
Cortés, M. L.
Estradé, A.
Fukuda, N.
Holl, M.
Itahashi, K.
Iwasa, N.
Jansen, G. R.
Jiang, W. G.
Kaur, S.
Macchiavelli, A. O.
Matsumoto, S. Y.
Momiyama, S.
Murray, I.
Nakamura, T.
Novario, S. J.
Ong, H. J.
Otsuka, T.
Papenbrock, T.
Paschalis, S.
Prochazka, A.
Scheidenberger, C.
Schrock, P.
Shimizu, Y.
Steppenbeck, D.
Sakurai, H.
Suzuki, D.
Suzuki, H.
Takechi, M.
Takeda, H.
Takeuchi, S.
Taniuchi, R.
Wimmer, K.
Yoshida, K.
Source :: Phys. Rev. Lett. 124, 222504 (2020)
Publication Year :: 2020
Abstract: We report the measurement of reaction cross sections ($\sigma_R^{\rm ex}$) of $^{27,29}$F with a carbon target at RIKEN. The unexpectedly large $\sigma_R^{\rm ex}$ and derived matter radius identify $^{29}$F as the heaviest two-neutron Borromean halo to date. The halo is attributed to neutrons occupying the $2p_{3/2}$ orbital, thereby vanishing the shell closure associated with the neutron number $N = 20$. The results are explained by state-of-the-art shell model calculations. Coupled-cluster computations based on effective field theories of the strong nuclear force describe the matter radius of $^{27}$F but are challenged for $^{29}$F.<br />Comment: 8 pages, 4 figures