Precise Measurement of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi mathvariant="normal">Λ</mi></mrow></math>-Binding-Energy Difference between <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mmultiscripts><mrow><mi mathvariant="normal">H</mi></mrow><mprescripts></mprescripts><mrow><mi mathvariant="normal">Λ</mi></mrow><mrow><mn>3</mn></mrow></mmultiscripts></mrow></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mmultiscripts><mrow><mi mathvariant="normal">H</mi></mrow><mprescripts></mprescripts><mrow><mi mathvariant="normal">Λ</mi></mrow><mrow><mn>4</mn></mrow></mmultiscripts></mrow></math> via Decay-Pion Spectroscopy at MAMI

A1 Collaboration; Ryoko Kino; Sho Nagao; Patrick Achenbach; Satoshi N. Nakamura; Josef Pochodzalla; Takeru Akiyama; Ralph Böhm; Mirco Christmann; Michael O. Distler; Luca Doria; Anselm Esser; Julian Geratz; Christian Helmel; Matthias Hoek; Tatsuhiro Ishige; Masashi Kaneta; Pascal Klag; David Markus; Harald Merkel; Masaya Mizuno; Ulrich Müller; Kotaro Nishi; Ken Nishida; Kazuki Okuyama; Jonas Pätschke; Björn Sören Schlimme; Concettina Sfienti; Tianhao Shao; Daniel Steger; Marcell Steinen; Liguang Tang; Michaela Thiel; Philipp Vonwirth; Luca Wilhelm

doi:10.1103/19gd-jqw2

Precise Measurement of the $Λ$ -Binding-Energy Difference between ${}_{Λ}^{3}H$ and ${}_{Λ}^{4}H$ via Decay-Pion Spectroscopy at MAMI

Ryoko Kino ^1,*, Sho Nagao^2,3,†, Patrick Achenbach⁴, Satoshi N. Nakamura^2,3,5, Josef Pochodzalla^4,6, Takeru Akiyama^5,7, Ralph Böhm⁸, Mirco Christmann⁴, Michael O. Distler⁴ et al. (A1 Collaboration)

Michael O. Distler⁴, Luca Doria⁴, Anselm Esser⁴, Julian Geratz⁴, Christian Helmel⁴, Matthias Hoek⁴, Tatsuhiro Ishige^5,7, Masashi Kaneta⁵, Pascal Klag⁴, David Markus⁴, Harald Merkel⁴, Masaya Mizuno⁵, Ulrich Müller⁴, Kotaro Nishi², Ken Nishida², Kazuki Okuyama^5,7, Jonas Pätschke⁴, Björn Sören Schlimme⁴, Concettina Sfienti⁴, Tianhao Shao^9,4, Daniel Steger⁴, Marcell Steinen⁴, Liguang Tang^10,11, Michaela Thiel⁴, Philipp Vonwirth⁴, and Luca Wilhelm⁴ (A1 Collaboration)

¹RIKEN Nishina Center for Accelerator-Based Science, Saitama 351-0198, Japan
²Department of Physics, Graduate School of Science, The University of Tokyo, Tokyo 113-0033, Japan
³Quark Nuclear Science Institute, Graduate School of Science, The University of Tokyo, Tokyo 113-0033, Japan
⁴Institute for Nuclear Physics, Johannes Gutenberg University Mainz, 55099 Mainz, Germany
⁵Department of Physics, Graduate School of Science, Tohoku University, Miyagi 980-8578, Japan
⁶Helmholtz Institute Mainz, GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, and Johannes Gutenberg University Mainz, 55099 Mainz, Germany
⁷Graduate Program on Physics for the Universe (GP-PU), Tohoku University, Miyagi 980-8578, Japan
⁸Facility for Antiproton and Ion Research (FAIR), 64291 Darmstadt, Germany
⁹Key Laboratory of Nuclear Physics and Ion-beam Application (MOE), Institute of Modern Physics, Fudan University, 200433 Shanghai, China
¹⁰Department of Physics, Hampton University, Hampton, Virginia 23668, USA
¹¹Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, USA

^*Contact author: ryoko.kino@riken.jp
^†Contact author: sho.nagao@nex.phys.s.u-tokyo.ac.jp

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Phys. Rev. Lett. 136, 152301 – Published 17 April, 2026

DOI: https://doi.org/10.1103/19gd-jqw2

Abstract

We performed high-precision decay-pion spectroscopy of light $Λ$ hypernuclei at the Mainz Microtron (MAMI) using the A1 spectrometer facility. By measuring the monochromatic $π^{-}$ momentum from the two-body weak decay ${}_{Λ}^{3}H \to {}^{3}{He} + π^{-}$ and referencing it to the ${}_{Λ}^{4}H \to {}^{4}{He} + π^{-}$ decay, we determined the $Λ$ binding energy of ${}_{Λ}^{3}H$ with unprecedented accuracy. The obtained value, $B_{Λ} (_{Λ}^{3} H) = 0.523 \pm 0.01 3_{stat} \pm 0.07 5_{syst} . MeV$ , is consistent with the STAR result, but indicates a significantly deeper binding than inferred from earlier measurements. This result implies a stronger $Λ$ -deuteron interaction and provides stringent constraints on hyperon-nucleon interactions.

Physical Review Letters

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Precise Measurement of the $Λ$ -Binding-Energy Difference between ${}_{Λ}^{3}H$ and ${}_{Λ}^{4}H$ via Decay-Pion Spectroscopy at MAMI

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Precise Measurement of the Λ-Binding-Energy Difference between HΛ3 and HΛ4 via Decay-Pion Spectroscopy at MAMI

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Precise Measurement of the $Λ$ -Binding-Energy Difference between ${}_{Λ}^{3}H$ and ${}_{Λ}^{4}H$ via Decay-Pion Spectroscopy at MAMI