arXiv · 2603.24341
The dipole strength distribution of $^8$He and decay characteristics
Abstract
The weak binding and spatially extended neutron densities characteristic of drip-line nuclei give rise to a distinctive low-energy dipole response. The drip-line nucleus $^8$He is the most neutron-rich bound nucleus with a mass-to-charge ratio of $A/Z=4$. We measure the dipole response of $^8$He, including for the first time the four-neutron decay channel. A total dipole strength of $\sum B(E1)(E^*<15$~MeV$)=0.95(16)~e^2$fm$^2$ and a dipole polarizability of $\alpha_D = 0.61(1)$~fm$^3$ are extracted from the differential Coulomb-excitation cross section and compared to state-of-the-art theoretical calculations employing coupled cluster and three-body approaches. We find that the dipole continuum is dominated, even at high excitation energies well above the $4n$ decay threshold, by two-neutron emission, pointing to a $^6$He$+2n$ structure of the excited dipole mode. No indication was found for a $4n$ final-state correlation, while pronounced $nn$ and $^6$He-$n$ final-state correlations are apparent.
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C. Lehr, T. Aumann, M. Duer, A. T. Saito, T. Nakamura, N. L. Achouri, D. Ahn, H. Baba, S. Bacca, C. A. Bertulani, M. Böhmer, F. Bonaiti, K. Boretzky, C. Caesar, N. Chiga, D. Cortina-Gil, C. A. Douma, F. Dufter, Z. Elekes, J. Feng, B. Fernández-Domínguez, U. Forsberg, N. Fukuda, I. Gasparic, Z. Ge, R. Gernhäuser, J. M. Gheller, J. Gibelin, A. Gillibert, K. I. Hahn, Z. Halász, M. N. Harakeh, A. Hirayama, M. Holl, N. Inabe, T. Isobe, J. Kahlbow, N. Kalantar-Nayestanaki, D. Kim, S. Kim, T. Kobayashi, Y. Kondo, D. Körper, P. Koseoglou, Y. Kubota, P. J. Li, S. Lindberg, Y. Liu, F. M. Marqués, S. Masuoka, M. Matsumoto, J. Mayer, K. Miki, M. Miwa, B. Monteagudo, A. Obertelli, N. A. Orr, H. Otsu, V. Panin, S. Y. Park, M. Parlog, S. Paschalis, P. M. Potlog, S. Reichert, A. Revel, D. M. Rossi, R. Roth, M. Sasano, H. Scheit, F. Schindler, T. Shimada, S. Shimoura, H. Simon, S. Storck Dutine, L. Stuhl, H. Suzuki, D. Symochko, H. Takeda, S. Takeuchi, J. Tanaka, Y. Togano, T. Tomai, H. T. Törnqvist, J. Tscheuschner, T. Uesaka, V. Wagner, H. Yamada, B. Yang, L. Yang, Z. H. Yang, M. Yasuda, K. Yoneda, L. Zanetti, J. Zenihiro. 2026-03-25. The dipole strength distribution of $^8$He and decay characteristics. https://doi.org/10.1103/vp3m-5rpp
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