Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Measurement of the mass difference and the binding energy of the hypertriton and antihypertriton


According to the CPT theorem, which states that the combined operation of charge conjugation, parity transformation and time reversal must be conserved, particles and their antiparticles should have the same mass and lifetime but opposite charge and magnetic moment. Here, we test CPT symmetry in a nucleus containing a strange quark, more specifically in the hypertriton. This hypernucleus is the lightest one yet discovered and consists of a proton, a neutron and a Λ hyperon. With data recorded by the STAR detector1,2,3 at the Relativistic Heavy Ion Collider, we measure the Λ hyperon binding energy BΛ for the hypertriton, and find that it differs from the widely used value4 and from predictions5,6,7,8, where the hypertriton is treated as a weakly bound system. Our results place stringent constraints on the hyperon–nucleon interaction9,10 and have implications for understanding neutron star interiors, where strange matter may be present11. A precise comparison of the masses of the hypertriton and the antihypertriton allows us to test CPT symmetry in a nucleus with strangeness, and we observe no deviation from the expected exact symmetry.

This is a preview of subscription content, access via your institution

Access options

Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Fig. 1: A typical \(_{\bar{\Lambda }}^{3}\overline{{\rm{H}}}\) 3-body decay in the detectors.
Fig. 2: Particle identification and the invariant mass distributions for \(_{\Lambda }^{3}{\rm{H}}\) and \(_{\bar{\Lambda }}^{3}\overline{{\rm{H}}}\) reconstruction.
Fig. 3: Measurements of the relative mass-to-charge ratio differences between nuclei and antinuclei.
Fig. 4: Measured Λ binding energy in the hypertriton compared to earlier results and theoretical calculations.

Data availability

All raw data for this study were collected by the STAR detector at Brookhaven National Laboratory. Data tables for the results reported in this Letter are publicly available on the STARwebsite ( or from the corresponding authors upon reasonable request.


  1. Anderson, M. et al. The STAR Time Projection Chamber: a unique tool for studying high multiplicity events at RHIC. Nucl. Inst. Methods Phys. Res. A 499, 659–678 (2003).

    ADS  Article  Google Scholar 

  2. Contin, G. et al. The STAR MAPS-based pixel detector. Nucl. Inst. Methods Phys. Res. A 907, 60–80 (2018).

    ADS  Article  Google Scholar 

  3. Llope, W. J. & The STAR Collaboration. Multigap RPCs in the STAR experiment at RHIC. Nucl. Inst. Methods Phys. Res. A 661, S110–S113 (2012).

    Article  Google Scholar 

  4. Juric, M. et al. A new determination of the binding-energy values of the light hypernuclei \(\left(A\le 15\right)\). Nucl. Phys. B 52, 1–30 (1973).

    ADS  Article  Google Scholar 

  5. Haidenbauer, J., Meißner, U.-G. & Nogga, A. Hyperon–nucleon interaction within chiral effective field theory revisited. Preprint at (2019).

  6. Miyagawa, K., Kamada, H., Glöckle, W. & Stoks, V. Properties of the bound Λ (Σ)NN system and hyperon–nucleon interactions. Phys. Rev. C 51, 2905–2913 (1995).

    ADS  Article  Google Scholar 

  7. Nogga, A., Kamada, H. & Glöckle, W. The hypernuclei \(_{\Lambda }^{4}{\rm{He}}\) and \(_{\Lambda }^{4}{\rm{H}}\): challenges for modern hyperon–nucleon forces. Phys. Rev. Lett. 88, 172501 (2002).

    ADS  Article  Google Scholar 

  8. Wirth, R. et al. Ab initio description of p-shell hypernuclei. Phys. Rev. Lett. 113, 192502 (2014).

    ADS  Article  Google Scholar 

  9. Hammer, H.-W. The hypertriton in effective field theory. Nucl. Phys. A 705, 173–189 (2002).

    ADS  Article  Google Scholar 

  10. Abelev, B. I. et al. Star Collaboration. Observation of an antimatter hypernucleus. Science 328, 58–62 (2010).

    ADS  Article  Google Scholar 

  11. Chatterjee, D. & Vidaña, I. Do hyperons exist in the interior of neutron stars? Eur. Phys. J. A 52, 1–18 (2016).

    Article  Google Scholar 

  12. Tanabashi, M. et al. Particle Data Group. Review of particle physics. Phys. Rev. D 98, 030001 (2018).

    ADS  Article  Google Scholar 

  13. Adam, J. et al. ALICE Collaboration. Precision measurement of the mass difference between light nuclei and anti-nuclei. Nat. Phys. 11, 811–814 (2015).

    Article  Google Scholar 

  14. Chatrchyan, S. et al. CMS Collaboration. Measurement of the mass difference between top quark and antiquark in pp collisions at \(\sqrt{s}\) = 8 TeV. Phys. Lett. B 770, 50–71 (2017).

    ADS  Article  Google Scholar 

  15. Aad, G. et al. ATLAS Collaboration. Measurement of the mass difference between top and anti-top quarks in pp collisions at \(\sqrt{s}\) = 7 TeV using the ATLAS detector. Phys. Lett. B 728, 363–379 (2014).

    ADS  Article  Google Scholar 

  16. Chan, A. W. et al. E756 Collaboration. Measurement of the properties of the \({\overline{\Omega }}^{+}\) and Ω hyperons. Phys. Rev. D 58, 072002 (1998).

    ADS  Article  Google Scholar 

  17. Kostelecký, V. A. & Russell, N. Data tables for Lorentz and CPT violation. Rev. Mod. Phys. 83, 11–31 (2011).

    ADS  Article  Google Scholar 

  18. Colladay, D. & Kostelecký, V. A. CPT violation and the standard model. Phys. Rev. D 55, 6760 (1997).

    ADS  Article  Google Scholar 

  19. Beane, S. R. et al. NPLQCD Collaboration. Light nuclei and hypernuclei from quantum chromodynamics in the limit of Su(3) flavor symmetry. Phys. Rev. D 87, 034506 (2013).

    ADS  Article  Google Scholar 

  20. Achenbach, P., Bleser, S., Pochodzalla, J. & Steinen, M. High-precision measurement of the hypertriton mass. PoS Hadron 2017, 207 (2018).

    Google Scholar 

  21. Acharya, S. et al. ALICE Collaboration. \(_{\Lambda }^{3}{\rm{H}}\) and \(_{\bar{\Lambda }}^{3}{\overline{\rm{H}}}\) lifetime measurement in Pb–Pb collisions at \(\sqrt{s_{\mathrm{NN}}}\) = 5.02 TeV via two-body decay. Phys. Lett. B 797, 134905 (2019).

    Article  Google Scholar 

  22. Adamczyk, L. et al. STAR Collaboration. 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).

    ADS  Article  Google Scholar 

  23. Lonardoni, D., Lovato, A., Gandolfi, S. & Pederiva, F. Hyperon puzzle: hints from quantum Monte Carlo calculations. Phys. Rev. Lett. 114, 092301 (2015).

    ADS  Article  Google Scholar 

  24. Fortin, M., Avancini, S. S., Providência, C. & Vidaña, I. Hypernuclei and massive neutron stars. Phys. Rev. C 95, 065803 (2017).

    ADS  Article  Google Scholar 

  25. Contessi, L., Barnea, N. & Gal, A. Resolving the Λ hypernuclear overbinding problem in pionless effective field theory. Phys. Rev. Lett. 121, 102502 (2018).

    ADS  Article  Google Scholar 

  26. Chen, J. H., Keane, D., Ma, Y. G., Tang, A. H. & Xu, Z. B. Antinuclei in heavy-ion collisions. Phys. Rep. 760, 1–39 (2018).

    ADS  MathSciNet  Article  Google Scholar 

  27. Mohr, P. J., Newell, D. B. & Taylor, B. N. CODATA recommended values of the fundamental physical constants: 2014. Rev. Mod. Phys. 88, 035009 (2016).

    ADS  Article  Google Scholar 

  28. Gajewski, W. et al. A compilation of binding energy values of light hypernuclei. Nucl. Phys. B 1, 105–113 (1967).

    ADS  Article  Google Scholar 

  29. Bohm, G. et al. A determination of the binding-energy values of light hypernuclei. Nucl. Phys. B 4, 511–526 (1968).

    ADS  Article  Google Scholar 

  30. Keyes, G. et al. Properties of ΛH3. Phys. Rev. D 1, 66–77 (1970).

    ADS  Article  Google Scholar 

  31. Davis, D. H. 50 years of hypernuclear physics: I. The early experiments. Nucl. Phys. A 754, 3–13 (2005).

    ADS  Article  Google Scholar 

  32. Dalitz, R. H., Herndon, R. C. & Tang, Y. C. Phenomenological study of s-shell hypernuclei with ΛN and ΛNN potentials. Nucl. Phys. B 47, 109–137 (1972).

    ADS  Article  Google Scholar 

  33. Fujiwara, Y., Suzuki, Y., Kohno, M. & Miyagawa, K. Addendum to triton and hypertriton binding energies calculated from SU6 quark-model baryon–baryon interactions. Phys. Rev. C 77, 027001 (2008).

    ADS  Article  Google Scholar 

  34. Lonardoni, D. & Pederiva, F. Medium-mass hypernuclei and the nucleon-isospin dependence of the three-body hyperon–nucleon–nucleon force. Preprint at (2018).

  35. Hildenbrand, F. & Hammer, H.-W. Three-body hypernuclei in pionless effective field theory. Phys. Rev. C 100, 034002 (2019).

    ADS  Article  Google Scholar 

  36. Le, H., Haidenbauer, J., Meißner, U.-G. & Nogga, A. Implications of an increased Λ-separation energy of the hypertriton. Phys. Lett. B 801, 135189 (2020).

    Article  Google Scholar 

Download references


The STAR Collaboration acknowledges contributions from V. Dexheimer, F. Hildenbrand and H.-W. Hammer. We thank the Relativistic Heavy Ion Collider (RHIC) Operations Group and the RHIC Computing Facility (RCF) at Brookhaven National Laboratory (BNL), the National Energy Research Scientific Computing (NERSC) Center at Lawrence Berkeley National Laboratory and the Open Science Grid Consortium for providing resources and support. This work was supported in part by the Office of Nuclear Physics within the US Department of Energy Office of Science, the US National Science Foundation, the Ministry of Education and Science of the Russian Federation, the National Natural Science Foundation of China, Chinese Academy of Science, the Ministry of Science and Technology of China and the Chinese Ministry of Education, the National Research Foundation of Korea, the Czech Science Foundation and Ministry of Education, Youth and Sports of the Czech Republic, the Hungarian National Research, Development and Innovation Office, the New National Excellency Programme of the Hungarian Ministry of Human Capacities, the Department of Atomic Energy and Department of Science and Technology of the Government of India, the National Science Centre of Poland, the Ministry of Science, Education and Sports of the Republic of Croatia, RosAtom of Russia and the German Bundesministerium für Bildung, Wissenschaft, Forschung und Technologie (BMBF) and the Helmholtz Association.

Author information

Authors and Affiliations



All authors made important contributions to this publication, in one or more of the areas of detector hardware and software, operation of the experiment, acquisition of data and data analysis. All STAR collaborations who are authors reviewed and approved the submitted manuscript.

Corresponding authors

Correspondence to J. H. Chen or P. Liu.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Peer review information Nature Physics thanks Stefan Ulmer and the other, anonymous, reviewer(s) 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.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

The STAR Collaboration. Measurement of the mass difference and the binding energy of the hypertriton and antihypertriton. Nat. Phys. 16, 409–412 (2020).

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI:

This article is cited by


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing