Abstract
A hypernucleus, a subatomic bound system with at least one hyperon, is a great test ground to investigate nuclear forces and general baryonic interactions with up, down and strange quarks. Hypernuclei have been extensively studied for almost seven decades in reactions involving cosmic rays and with accelerator beams. In recent years, experimental studies of hypernuclei have entered a new stage using energetic collisions of heavy-ion beams. However, these investigations have revealed two puzzling results related to the lightest three-body hypernuclear system, the so-called hypertriton, and the unexpected existence of a bound state of two neutrons with a Λ hyperon. Solving these puzzles will not only impact our understanding of the fundamental baryonic interactions with strange quarks but also of the nature of the deep interior of neutron stars. In this Perspective, we discuss approaches to solving these puzzles, including experiments with heavy-ion beams and the analysis of nuclear emulsions using state-of-the-art technologies. We summarize ongoing projects and experiments at various facilities worldwide and outline future perspectives.
This is a preview of subscription content, access via your institution
Relevant articles
Open Access articles citing this article.
-
Status of the high-intensity heavy-ion accelerator facility in China
AAPPS Bulletin Open Access 08 November 2022
Access options
Access Nature and 54 other Nature Portfolio journals
Get Nature+, our best-value online-access subscription
$29.99 / 30 days
cancel any time
Subscribe to this journal
Receive 12 digital issues and online access to articles
$99.00 per year
only $8.25 per issue
Rent or buy this article
Get just this article for as long as you need it
$39.95
Prices may be subject to local taxes which are calculated during checkout



References
Weber, F. Strangeness in neutron stars. J. Phys. G Nucl. Part. Phys. 27, 465–474 (2001).
Weber, F., Ho, A., Negreiros, R. P. & Rosenfield, P. Strangeness in neutron stars. Int. J. Mod. Phys. D 16, 231–245 (2007).
Demorest, P. B., Pennucci, T., Ransom, S. M., Roberts, M. S. E. & Hessels, J. W. T. A two-solar-mass neutron star measured using Shapiro delay. Nature 467, 1081–1083 (2010).
Antoniadis, J. et al. A massive pulsar in a compact relativistic binary. Science 340, 1233232 (2013).
Barr, E. D. et al. A massive millisecond pulsar in an eccentric binary. Mon. Not. R. Astron. Soc. 465, 1711–1719 (2016).
Yamamoto, Y., Furumoto, T., Yasutake, N. & Rijken, T. A. Hyperon mixing and universal many-body repulsion in neutron stars. Phys. Rev. C 90, 045805 (2014).
Ekawa, H. et al. Observation of a Be double-Lambda hypernucleus in the J-PARC E07 experiment. Prog. Theor. Exp. Phys. 2019, 021D02 (2019).
Hayakawa, S. H. et al. Observation of coulomb-assisted nuclear bound state of Ξ−–14N system. Phys. Rev. Lett. 126, 062501 (2021).
Takahashi, H. et al. Observation of a \({}_{\Lambda \Lambda }^{6}{\rm{He}}\) double hypernucleus. Phys. Rev. Lett. 87, 212502 (2001).
Nakazawa, K. & Takahashi, H. Experimental study of double-Λ hypernuclei with nuclear emulsion. Prog. Theor. Phys. Suppl. 185, 335–343 (2010).
Rappold, C. et al. Hypernuclear production cross section in the reaction of 6Li + 12C at 2 A GeV. Phys. Lett. B 747, 129–134 (2015).
The STAR Collaboration Observation of an antimatter hypernucleus. Science 328, 58–62 (2010).
Xu, Y. for the STAR Collaboration in Proceedings of the 12th International Conference on Hypernuclear and Strange Particle Physics (HYP2015) 021005 (2017).
Adamczyk, L. et al. Measurement of the \({\,}_{\Lambda }^{3}{\rm{H}}\) lifetime in Au+Au collisions at the BNL Relativistic Heavy Ion Collider. Phys. Rev. C 97, 054909 (2018).
Chen, J., Keane, D., Ma, Y.-G., Tang, A. & Xu, Z. Antinuclei in heavy-ion collisions. Phys. Rep. 760, 1–39 (2018).
Adam, J. et al. \({\,}_{\Lambda }^{3}{\rm{H}}\) and \({\,}_{\bar{\Lambda }}^{3}\bar{{\rm{H}}}\) production in Pb–Pb collisions at \(\sqrt{{s}_{{\rm{NN}}}}\) = 2.76 TeV. Phys. Lett. B 754, 360–372 (2016).
Acharya, S. et al. \({\,}_{\Lambda }^{3}{\rm{H}}\) and \({\,}_{\bar{\Lambda }}^{3}\bar{{\rm{H}}}\) lifetime measurement in Pb–Pb collisions at \(\sqrt{{s}_{{\rm{NN}}}}\) = 5.02 TeV via two-body decay. Phys. Lett. B 797, 134905 (2019).
Adam, J. et al. Measurement of the mass difference and the binding energy of the hypertriton and antihypertriton. Nat. Phys. 16, 409–412 (2020).
Rappold, C. et al. Search for evidence of \({\,}_{\Lambda }^{3}n\) by observing d + π− and t + π− final states in the reaction of 6Li+12C at 2A GeV. Phys. Rev. C 88, 041001 (2013).
Davis, D. H. 50 years of hypernuclear physics: I. The early experiments. Nucl. Phys. A 754, 3–13 (2005).
Bohm, G. et al. A determination of the binding-energy values of light hypernuclei. Nucl. Phys. B 4, 511–526 (1968).
JuriÄ, M. et al. A new determination of the binding-energy values of the light hypernuclei (A ≤ 15). Nucl. Phys. B 52, 1–30 (1973).
Prem, R. J. & Steinberg, P. H. Lifetimes of hypernuclei, ΛH3, ΛH4, ΛH5. Phys. Rev. 136, B1803–B1806 (1964).
Keyes, G. et al. New measurement of the ΛH3 lifetime. Phys. Rev. Lett. 20, 819–821 (1968).
Phillips, R. E. & Schneps, J. Lifetimes of light hyperfragments. II. Phys. Rev. 180, 1307–1318 (1969).
Bohm, G. et al. On the lifetime of the \({}_{\Lambda }^{3}{\rm{H}}\) hypernucleus. Nucl. Phys. B 16, 46–52 (1970).
Keyes, G. et al. Properties of ΛH3. Phys. Rev. D 1, 66–77 (1970).
Keyes, G., Sacton, J., Wickens, J. & Block, M. A measurement of the lifetime of the \({}_{\Lambda }^{3}{\rm{H}}\) hypernucleus. Nucl. Phys. B 67, 269–283 (1973).
Particle Data Group et al.Review of particle physics. Prog. Theor. Exp. Phys. 2020, 083C01 (2020).
Rappold, C. et al. Hypernuclear spectroscopy of products from 6Li projectiles on a carbon target at 2 AGeV. Nucl. Phys. A 913, 170–184 (2013).
Yu-Gang, M. (Anti)hypertriton lifetime puzzle. EPJ Web Conf. 117, 03003 (2016).
Perez-Obiol, A., Gazda, D., Friedman, E. & Gal, A. Revisiting the hypertriton lifetime puzzle. Phys. Lett. B 811, 135916 (2020).
Hildenbrand, F. & Hammer, H.-W. Lifetime of the hypertriton. Phys. Rev. C 102, 064002 (2020).
Hiyama, E. et al. Three-body structure of the nnΛ system with ΛN–ΣN coupling. Phys. Rev. C 89, 061302 (2014).
Gal, A. & Garcilazo, H. Is there a bound \({}_{\Lambda }^{3}{\rm{n}}\)? Phys. Lett. B 736, 93–97 (2014).
Garcilazo, H. & Valcarce, A. Nonexistence of a Λnn bound state. Phys. Rev. C 89, 057001 (2014).
Schafer, M. et al. The continuum spectrum of hypernuclear trios. Phys. Lett. B 808, 135614 (2020).
Ando, S.-I., Raha, U. & Oh, Y. Investigation of the nnΛ bound state in pionless effective theory. Phys. Rev. C 92, 024325 (2015).
Hildenbrand, F. & Hammer, H.-W. Three-body hypernuclei in pionless effective field theory. Phys. Rev. C 100, 034002 (2019).
Afnan, I. R. & Gibson, B. F. Resonances in the Λnn system. Phys. Rev. C 92, 054608 (2015).
Tang, L. et al. Determining the unknown Λ-n interaction by investigating the Λnn Resonance. Approved proposal E12-17-003 by PAC at Jefferson Lab. https://www.jlab.org/exp_prog/proposals/17/PR12-17-003.pdf (2017).
Bleser, S. et al. Has the neutral double hypernucleus \({}_{\Lambda \Lambda }^{4}{\rm{n}}\) been observed? Phys. Lett. B 790, 502–508 (2019).
Le, H., Haidenbauer, J., Meiner, U.-G. & Nogga, A. Implications of an increased λ-separation energy of the hypertriton. Phys. Lett. B 801, 135189 (2020).
Haidenbauer, J., Meißner, U.-G. & Nogga, A. Hyperon–nucleon interaction within chiral effective field theory revisited. Eur. Phys. J. A 56, 91 (2020).
Geissel, H. et al. The GSI projectile fragment separator (FRS): a versatile magnetic system for relativistic heavy ions. Nucl. Instrum. Methods Phys. Res. B 70, 286–297 (1992).
Bargholtz, C. et al. The WASA detector facility at CELSIUS. Nucl. Instrum. Methods Phys. Res. A 594, 339–350 (2008).
Saito, T. R. et al. Studies of the d+π− signal and lifetime of the \({}_{\Lambda }^{3}{\rm{H}}\) and \({}_{\Lambda }^{4}{\rm{H}}\) hypernuclei by new spectroscopy techniques with FRS. Approved proposal S447 by GSI G-PAC (2017).
Outa, H. et al. Mesonic and non-mesonic decay widths of \({}_{\Lambda }^{4}{\rm{H}}\) and \({}_{\Lambda }^{4}{\rm{He}}\). Nucl. Phys. A 639, 251c–260c (1998).
Facility for Antiproton and Ion Research in Europe (FAIR). https://fair-center.eu.
High Intensity Heavy-ion Accelerator Facility (HIAF). http://hiaf.impcas.ac.cn/hiaf_en/public/c/news.html.
Imai, K., Nakazawa, K. & Tamura, H. J-PARC E07 experiment: Systematic study of double strangeness system with an emulsion-counter hybrid method. Proposal for Nuclear and Particle Physics Experiments at J-PARC (2006). http://j-parc.jp/researcher/Hadron/en/pac_0606/pdf/p07-Nakazawa.pdf.
Aoki, S. et al. Nuclear capture at rest of Ξ− hyperons. Nucl. Phys. A 828, 191–232 (2009).
Ahn, J. K. et al. Double-Λ hypernuclei observed in a hybrid emulsion experiment. Phys. Rev. C 88, 014003 (2013).
LeCun, Y., Bengio, Y. & Hinton, G. Deep learning. Nature 521, 436–444 (2015).
He, K., Zhang, X., Ren, S. & Sun, J. Deep residual learning for image recognition. Preprint at arXiv http://arxiv.org/abs/1512.03385 (2015).
Yoshida, J. et al. CNN-based event classification of alpha-decay events in nuclear emulsion. Nucl. Instrum. Methods Phys. Res. A 989, 164930 (2021).
Goodfellow, I. J. et al. Generative adversarial networks. Preprint at arXiv https://arxiv.org/abs/1406.2661 (2014).
Wang, T. et al. High-resolution image synthesis and semantic manipulation with conditional GANs. Preprint at arXiv http://arxiv.org/abs/1711.11585 (2017).
He, K., Gkioxari, G., Dollár, P. & Girshick, R. B. Mask R-CNN. Preprint at arXiv https://arxiv.org/abs/1703.06870 (2017).
Barkas, W. H. Nuclear Research Emulsions. Pure & Applied Physics Series 15-1 (Academic, 1963).
Danysz, M. et al. The identification of a double hyperfragment. Nucl. Phys. 49, 121–132 (1963).
Dalitz, R. H. et al. The identified ΛΛ-hypernuclei and the predicted H-particle. Proc. R. Soc. Lond. A Math. Phys. Sci. 426, 1–17 (1989).
Aoki, S. et al. Direct observation of sequential weak decay of a double hypernucleus. Prog. Theor. Phys. 85, 1287–1298 (1991).
Nakazawa, K. et al. The first evidence of a deeply bound state of Xi−–14N system. Prog. Theor. Exp. Phys. 2015, 033D02 (2015).
Ichikawa, A. et al. Production of twin Λ-hypernuclei from Ξ− hyperon capture at rest. Phys. Lett. B 500, 37–46 (2001).
Yoshimoto, M. et al. First observation of a nuclear s-state of a Ξ hypernucleus, \({}_{\Xi }^{15}{\rm{C}}\). Prog. Theor. Exp. Phys. 2021, 073D02 (2021).
Yoshida, J., Nakazawa, K. & Umehara, K. New methods and technologies for double-lambda hypernucleus search in nuclear emulsion in J-PARC E07. https://doi.org/10.7566/JPSCP.1.013070 (2014).
Yoshida, J. et al. A new scanning system for alpha decay events as calibration sources for range-energy relation in nuclear emulsion. Nucl. Instrum. Methods Phys. Res. A 847, 86–92 (2017).
Yamamoto, T. O. et al. Observation of spin-dependent charge symmetry breaking in ΛN interaction: gamma-ray spectroscopy of \({}_{\Lambda }^{4}{\rm{He}}\). Phys. Rev. Lett. 115, 222501 (2015).
Superconducting fragment separator (Super-FRS). https://fair-center.eu/en/for-users/experiments/nustar/super-frs.html.
Rappold, C. & López-Fidalgo, J. Examination of experimental conditions for the production of proton-rich and neutron-rich hypernuclei. Phys. Rev. C 94, 044616 (2016).
Saito, T. R., Ekawa, H. & Nakagawa, M. Novel method for producing very-neutron-rich hypernuclei via charge-exchange reactions with heavy ion projectiles. Eur. Phys. J. A 57, 159 (2021).
Bass, S. et al. Microscopic models for ultrarelativistic heavy ion collisions. Prog. Part. Nucl. Phys. 41, 255–369 (1998).
Bleicher, M. et al. Relativistic hadron-hadron collisions in the ultra-relativistic quantum molecular dynamics model. J. Phys. G Nucl. Part. Phys. 25, 1859–1896 (1999).
Yang, J. et al. High intensity heavy ion accelerator facility (hiaf) in China. Nucl. Instrum. Methods Phys. Res. B 317, 263–265 (2013).
Kalantar-Nayestanaki, N. & Bruce, A. NUSTAR: NUclear STructure Astrophysics and Reactions at FAIR. Nucl. Phys. News 28, 5–11 (2018).
Danysz, M. & Pniewski, J. Delayed disintegration of a heavy nuclear fragment: I. Phil. Mag. 44, 348–350 (1953).
Hashimoto, O. & Tamura, H. Spectroscopy of Λ hypernuclei. Prog. Part. Nucl. Phys. 57, 564–653 (2006).
Saito, T. R. et al. Hypernuclei with stable heavy ion beam and RI-beam induced reactions at GSI (HypHI). Letter of intent submitted to GSI G-PAC (2005).
Saito, T. R. et al. Phase 0 experiment of the HypHI project: Hypernuclear spectroscopy of \({}_{\Lambda }^{3}{\rm{H}}\), \({}_{\Lambda }^{4}{\rm{H}}\) and \({}_{\Lambda }^{5}{\rm{He}}\)He with a 6Li beam at 2 A GeV on a 12C target. Proposal approved by GSI G-PAC (2006).
Acknowledgements
Discussions presented for the WASA-FRS experiment here are based on the experiment S447, which is currently scheduled in 2022 at the FRS at the GSI Helmholtzzentrum fuer Schwerionenforschung, Darmstadt (Germany) in the context of FAIR Phase 0. The authors thank the accelerator departments at GSI and IMP, the FRS department at GSI and the Experiment Electronics department at GSI for the technical support. The authors thank the J-PARC E07 collaboration for providing us with the nuclear emulsion data. The authors thank Luise Doersching-Steitz of GSI, Rita Krause of GSI, Yukiko Kurakata of RIKEN, Daniela Press of GSI, Miao Yang of IMP and Xiaohua Yuan of IMP for supporting the projects, including the administrative works. The authors also thank Risa Kobayashi of RIKEN and Yoko Tsuchii of Gifu University for their technical support in mining hypertriton events in the E07 nuclear emulsions. K.N., J.Y. and M.Y. acknowledge support by JSPS KAKENHI grant numbers JP23224006, JP16H02180, JP20H00155 and JP20J00682, and MEXT KAKENHI grant numbers JP24105002 (Grant-in-Aid for Scientific Research on Innovative Areas 2404), JP18H05403 and JP19H05147 (Grant-in-Aid for Scientific Research on Innovative Areas 6005). S.E. and C.R. are supported by the grant 2019-T1/TIC-13194 of the program ‘Atracción de Talento Investigador’ of the Community of Madrid.
Author information
Authors and Affiliations
Contributions
All authors contributed to the manuscript. T.R.S., V.D., H.E., S.E., N.K.-N., A.K., M.K., E.L., S.M., A.M., M.N., C.R., N.S., C.S., M.T., Y.K.T., J.Y. and H.W. contributed to the WASA-FRS experiment at GSI and will contribute to future hypernuclear projects at FAIR. T.R.S., W.D., H.E., A.K., E.L., A.M., M.N., K.N., C.R., N.S., M.T., Y.K.T., J.Y., M.Y. and H.W. contributed to the development of the method to analyse the nuclear emulsion with machine learning. T.R.S., H.E., Y.H., E.L., Y.M., M.N., C.R., H.W. and X.Z. are working on the hypernuclear project at HIAF.
Corresponding author
Ethics declarations
Competing interests
The authors declare no competing interests.
Additional information
Peer review information
Nature Reviews Physics thanks Yu-Gang Ma, Stefano Trogolo, Ed Hungerford and the other, anonymous, reviewer for their contribution to the peer review of this work.
Publisher’s note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Supplementary information
Rights and permissions
About this article
Cite this article
Saito, T.R., Dou, W., Drozd, V. et al. New directions in hypernuclear physics. Nat Rev Phys 3, 803–813 (2021). https://doi.org/10.1038/s42254-021-00371-w
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1038/s42254-021-00371-w
This article is cited by
-
The interplay of single-particle and collective motions in the low-lying states of $$_\Lambda ^{21}$$ with quadrupole-octupole correlations
Science China Physics, Mechanics & Astronomy (2023)
-
Gravitational-wave and X-ray probes of the neutron star equation of state
Nature Reviews Physics (2022)
-
Status of the high-intensity heavy-ion accelerator facility in China
AAPPS Bulletin (2022)