Letter
Open Access

Direct observation of three-neutron emission from ${}^{7}{He}^{*}$ and the search for the trineutron

S. W. Huang ^1,2,3, C. Lenain ⁴, Z. H. Yang ^1,2,*, F. M. Marqués ⁴, J. Gibelin ⁴, J. G. Li ^5,6,7, A. Matta ⁴, N. A. Orr ⁴, N. L. Achouri ⁴ et al.

D. S. Ahn^2,8,9, A. Anne ⁴, T. Aumann ^10,11, H. Baba², D. Beaumel ¹², M. Böhmer¹³, K. Boretzky ^11,2, M. Caamaño ¹⁴, N. Chen ^5,6, S. Chen¹⁵, N. Chiga², M. L. Cortés², D. Cortina¹⁴, P. Doornenbal ², C. A. Douma ¹⁶, F. Dufter¹³, J. Feng¹, B. Fernández-Domínguez ¹⁴, Z. Elekes ^17,18, U. Forsberg ^19,20, T. Fujino²¹, N. Fukuda², I. Gašparić ^22,2, Z. Ge², R. Gernhäuser ¹³, J. M. Gheller²³, A. Gillibert²³, Z. Halász ¹⁷, T. Harada^2,24, M. N. Harakeh ^11,16, A. Hirayama^25,2, N. Inabe², T. Isobe ², J. Kahlbow ^10,2, N. Kalantar-Nayestanaki ¹⁶, D. Kim⁸, S. Kim ⁸, S. Kiyotake²⁶, T. Kobayashi²⁷, D. Koerper¹¹, Y. Kondo²⁵, P. Koseoglou ^10,11, Y. Kubota ², I. Kuti ¹⁷, C. Lehr^10,2, P. J. Li ^28,15, Y. Liu¹, Y. Maeda ²⁶, S. Masuoka²⁹, M. Matsumoto^25,2, J. Mayer ³⁰, N. Michel ^5,6, H. Miki²⁵, M. Miwa^2,31, B. Monteagudo⁴, I. Murray², T. Nakamura ²⁵, A. Obertelli¹⁰, H. Otsu², V. Panin ², S. Park⁸, M. Parlog⁴, S. Paschalis ^10,19, P. M. Potlog ³², S. Reichert ¹³, A. Revel ^33,4, D. Rossi ^10,11, A. T. Saito²⁵, M. Sasano², H. Sato ², H. Scheit ¹⁰, F. Schindler¹⁰, T. Shimada²⁵, Y. Shimizu², S. Shimoura ²⁹, H. Simon ¹¹, I. Stefan ³⁴, S. Storck¹⁰, L. Stuhl ^29,8, H. Suzuki², D. Symochko ¹⁰, H. Takeda², S. Takeuchi²⁵, J. Tanaka ¹⁰, Y. Togano ^2,21, T. Tomai ^25,2, H. T. Törnqvist ^10,11, E. Tronchin ⁴, J. Tscheuschner¹⁰, V. Wagner¹⁰, K. Wimmer ²⁹, M. R. Xie ^5,6, H. Yamada²⁵, B. Yang¹, L. Yang²⁹, M. Yasuda^25,2, Y. L. Ye ¹, K. Yoneda², L. Zanetti^10,2, J. Zenihiro ^2,35, and T. Uesaka²

¹School of Physics and State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing 100871, China
²RIKEN Nishina Center, Hirosawa 2-1, Wako, Saitama 351-0198, Japan
³Institute for Rare Isotope Science, Institute for Basic Science, Daejeon 34000, Republic of Korea
⁴Université de Caen Normandie, CNRS/IN2P3, ENSICAEN, LPC Caen, UMR6534, 14050 Caen Cedex, France
⁵Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China
⁶School of Nuclear Science and Technology, University of Chinese Academy of Sciences, Beijing 100049, China
⁷Southern Center for Nuclear-Science Theory (SCNT), Institute of Modern Physics, Chinese Academy of Sciences, Huizhou 516000, China
⁸CENS, Institute for Basic Science, Daejeon 34126, Republic of Korea
⁹Facility for Rare Isotope Beams, Michigan State University, East Lansing, MI 48824, USA
¹⁰Institut für Kernphysik, Technische Universität Darmstadt, D-64289 Darmstadt, Germany
¹¹GSI Helmholtzzentrum für Schwerionenforschung, 64291 Darmstadt, Germany
¹²Université Paris-Saclay, CNRS/IN2P3, IJCLab, 91405 Orsay, France
¹³Technical University of Munich, TUM School of Natural Sciences, 85747 Garching, Germany
¹⁴Departamento de Física de Partículas and IGFAE, Universidade de Santiago de Compostela, E-15782 Santiago de Compostela, Spain
¹⁵Department of Physics, The University of Hong Kong, Hong Kong, China
¹⁶ESRIG, University of Groningen, Zernikelaan 25, 9747 AA Groningen, The Netherlands
¹⁷Institute for Nuclear Research (HUN-REN ATOMKI), Debrecen, Hungary
¹⁸Institute of Physics, Faculty of Science and Technology, University of Debrecen, Egyetem tér 1, H-4032 Debrecen, Hungary
¹⁹School of Physics, Engineering and Technology, University of York, York YO10 5DD, United Kingdom
²⁰Department of Physics, Lund University, 22100 Lund, Sweden
²¹Department of Physics, Rikkyo University, 3-34-1, Nishi-Ikebukuro, Toshima, Tokyo 171-8501, Japan
²²Ruđer Bošković Institute (RBI), Zagreb, Croatia
²³Département de Physique Nucléaire, IRFU, CEA, Université Paris-Saclay, 91191 Gif-sur-Yvette, France
²⁴Department of Physics, Toho University, Funabashi, Chiba 274-8510, Japan
²⁵Department of Physics, Institute of Science Tokyo, 2-12-1 O-Okayama, Meguro, Tokyo 152-8551, Japan
²⁶Faculty of Engineering, University of Miyazaki, Miyazaki 889-2192, Japan
²⁷Department of Physics, Tohoku University, Aramaki Aza-Aoba 6-3, Aoba, Sendai, Miyagi 980-8578, Japan
²⁸Key Laboratory of Nuclear Physics and Ion-Beam Application (MOE), Institute of Modern Physics, Fudan University, Shanghai 200433, China
²⁹Center for Nuclear Study, University of Tokyo, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
³⁰Institut für Kernphysik, Universität zu Köln, Köln, Germany
³¹Department of Physics, Saitama University, Shimo-Okubo 255, Sakura-ku, Saitama-shi 338-8570, Japan
³²Institute of Space Science - INFLPR Subsidiary, Magurele, Romania
³³Grand Accélérateur National d’Ions Lourds (GANIL), CEA/DRF-CNRS/IN2P3, Bvd Henri Becquerel, 14076 Caen, France
³⁴Institut de Physique Nucléaire Orsay, IN2P3-CNRS, 91406 Orsay Cedex, France
³⁵Department of Physics, Kyoto University, Kitashirakawa, Sakyo, Kyoto 606-8502, Japan

^*Contact author: zaihong.yang@pku.edu.cn

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Phys. Rev. Research 8, L022003 – Published 1 April, 2026

DOI: https://doi.org/10.1103/sr8h-2n6v

Abstract

Three-neutron emission from ${}^{7}{He}$ has been directly measured for the first time, following neutron knockout from a ${}^{8}{He}$ beam at 156 MeV/nucleon. A resonancelike structure at 2.08(4) MeV above the ${}^{4}{He} + 3 n$ threshold $[E_{x} = 2.68 (4)$ MeV] with a width of 3.9(2) MeV was observed and deduced to arise predominately from the predicted $J^{π} = 3 / 2_{2}^{-}$ level. The three-neutron invariant-mass spectrum was reconstructed and found to peak at around 1 MeV and could, through complete simulations incorporating neutron-neutron correlations, be very well described by the sequential decay of ${}^{7}{He}^{*}$ via the $2_{1}^{+}$ excited state of ${}^{6}{He}$ . No evidence was found for any significant three-neutron correlations beyond those expected from well-established two-body interactions, including a trineutron resonance.

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Phys. Rev. Research 8, L022003– Published 1 April, 2026

Vol. 8, Iss. 2 — April - June 2026

Received 11 August 2025
Revised 15 December 2025
Accepted 10 February 2026

DOI: https://doi.org/10.1103/sr8h-2n6v

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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Direct observation of three-neutron emission from ${}^{7}{He}^{*}$ and the search for the trineutron

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Direct observation of three-neutron emission from He*7 and the search for the trineutron

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Direct observation of three-neutron emission from ${}^{7}{He}^{*}$ and the search for the trineutron