Observation of a correlated free four-neutron system

M. Duer*, T. Aumann, R. Gernhäuser, V. Panin, S. Paschalis, D. M. Rossi, N. L. Achouri, D. Ahn, H. Baba, C. A. Bertulani, M. Böhmer, K. Boretzky, C. Caesar, N. Chiga, A. Corsi, D. Cortina-Gil, C. A. Douma, F. Dufter, Z. Elekes, J. FengB. Fernández-Domínguez, U. Forsberg, N. Fukuda, I. Gasparic, Z. Ge, 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, T. Kobayashi, Y. Kondo, D. Körper, P. Koseoglou, Y. Kubota, I. Kuti, C. Lehr, S. Lindberg, F. M. Marqués, S. Masuoka, M. Matsumoto, J. Mayer, K. Miki, B. Monteagudo, T. Nakamura, T. Nilsson, A. Obertelli, N. A. Orr, H. Otsu, M. Parlog, P. M. Potlog, S. Reichert, A. Revel, A. T. Saito, M. Sasano, H. Scheit, F. Schindler, S. Shimoura, H. Simon, L. Stuhl, H. Suzuki, D. Symochko, H. Takeda, J. Tanaka, Y. Togano, T. Tomai, H. T. Törnqvist, J. Tscheuschner, T. Uesaka, V. Wagner, H. Yamada, M. Yasuda, K. Yoneda, L. Zanetti, J. Zenihiro, M. V. Zhukov

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


A long-standing question in nuclear physics is whether chargeless nuclear systems can exist. To our knowledge, only neutron stars represent near-pure neutron systems, where neutrons are squeezed together by the gravitational force to very high densities. The experimental search for isolated multi-neutron systems has been an ongoing quest for several decades1, with a particular focus on the four-neutron system called the tetraneutron, resulting in only a few indications of its existence so far2–4, leaving the tetraneutron an elusive nuclear system for six decades. Here we report on the observation of a resonance-like structure near threshold in the four-neutron system that is consistent with a quasi-bound tetraneutron state existing for a very short time. The measured energy and width of this state provide a key benchmark for our understanding of the nuclear force. The use of an experimental approach based on a knockout reaction at large momentum transfer with a radioactive high-energy 8He beam was key.

Original languageEnglish
Pages (from-to)678-682
Number of pages16
Issue number7915
Early online date22 Jun 2022
Publication statusPublished - 23 Jun 2022

Bibliographical note

© The Author(s) 2022

Funding Information:
We thank M. Göbel and H. W. Hammer for providing the theoretical input of the two-neutron energy distribution. This work was supported by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) Project-ID 279384907 - SFB 1245, the GSI-TU Darmstadt cooperation agreement, by the UK STFC under contract numbers ST/P003885/1 and ST/L005727/1 and the University of York Pump Priming Fund, by the German Federal Ministry of Education and Research - BMBF project numbers 05P15RDFN1, 05P15WOFNA and 05P15WOCIA, by project FAIR-RO-04/DEMAND - IFA, by JSPS KAKENHI grant numbers JP16H02177, JP16H02179 and JP18H05404, by the Spanish Research grant PGC2018-099746-B-C21, and by the Swedish Research Council, project grant 2011-5324 and 2017-03839. K.I.H., D. Kim, S.K., L.S., S.Y.P. and D.A. acknowledge the support from the IBS grant funded by the Korea government grant number IBS-R031-D1. C.A.B. acknowledges partial support by the US DOE grant number DE-FG02- 08ER41533. I.G. acknowledges support by HIC for FAIR and Croatian Science Foundation under project numbers 1257 and 7194. Z.E., Z.H. and I.K. acknowledge the support by NKFIH grants numbers 114454, 128947 and GINOP-2.3.3-15-2016-00034. The LPC group acknowledge support from the France-Japanese LIA-International Associated Laboratory for Nuclear Structure Problems as well as the French ANR-14-CE33-0022-02 EXPAND.

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