Quenching of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>π</mi><mn>0</mn><msub><mrow><mi>p</mi></mrow><mrow><mn>3</mn><mo>/</mo><mn>2</mn></mrow></msub><mo>−</mo><mi>π</mi><mn>0</mn><msub><mrow><mi>p</mi></mrow><mrow><mn>1</mn><mo>/</mo><mn>2</mn></mrow></msub></mrow></math> Spin-Orbit Splitting in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mmultiscripts><mrow><mi mathvariant="normal">O</mi></mrow><mprescripts></mprescripts><none></none><mrow><mn>20</mn></mrow></mmultiscripts></mrow></math> and the Effect of the Tensor Force

J. Lois-Fuentes; B. Fernández-Domínguez; T. Roger; F. Delaunay; M. Lozano-González; O. Sorlin; T. Otsuka; T. Suzuki; N. L. Achouri; M. Caamaño; C. Cabo; L. Caceres; A. Candiello; A. Cassisa; A. Ceulemans; F. Cresto; Q. Delignac; J. A. Dueñas; D. Fernández-Fernández; S. Fracassetti; J. Giovinazzo; S. Grévy; G. F. Grinyer; V. Guimarães; O. Kamalou; T. Kurtukian-Nieto; M. B. Latif; B. Mauss; C. Nicolle; A. Ortega-Moral; J. Pancin; J. Piot; O. Poleshchuk; R. Raabe; D. Ramos; D. Regueira-Castro; A. M. Sánchez-Benítez; J. C. Thomas; M. Vandebrouck; J. C. Zamora

doi:10.1103/6gyv-qr54

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Quenching of the $π 0 p_{3 / 2} - π 0 p_{1 / 2}$ Spin-Orbit Splitting in ${}^{20}O$ and the Effect of the Tensor Force

J. Lois-Fuentes ^1,*, B. Fernández-Domínguez ^1,†, T. Roger ², F. Delaunay ³, M. Lozano-González ¹, O. Sorlin ², T. Otsuka ⁴, T. Suzuki ^5,‡, N. L. Achouri ³ et al.

M. Caamaño ¹, C. Cabo ¹, L. Caceres ², A. Candiello ⁶, A. Cassisa ^7,8, A. Ceulemans ⁶, F. Cresto⁹, Q. Delignac⁹, J. A. Dueñas ¹⁰, D. Fernández-Fernández¹, S. Fracassetti⁶, J. Giovinazzo ⁹, S. Grévy ⁹, G. F. Grinyer ¹¹, V. Guimarães ¹², O. Kamalou², T. Kurtukian-Nieto ⁹, M. B. Latif⁶, B. Mauss ², C. Nicolle², A. Ortega-Moral⁹, J. Pancin², J. Piot ², O. Poleshchuk⁶, R. Raabe ⁶, D. Ramos ², D. Regueira-Castro¹, A. M. Sánchez-Benítez ¹³, J. C. Thomas ², M. Vandebrouck ¹⁴, and J. C. Zamora ¹²

¹IGFAE and Departamento de Física de Partículas, University of Santiago de Compostela, E-15758, Santiago de Compostela, Spain
²GANIL, CEA/DRF-CNRS/IN2P3, Bd. Henri Becquerel, BP 55027, F-14076 Caen, France
³LPC Caen UMR6534, Université de Caen Normandie, ENSICAEN, CNRS/IN2P3, F-14000 Caen, France
⁴CNS, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, Japan
⁵NAT Research Center, NAT Corporation, 3129-45 Hibara, Muramatsu, Tokai, Naka, 319-1112, Ibaraki, Japan
⁶KU Leuven, Instituut voor Kern- en Stralingsfysica, Celestijnenlaan 200d, 3001 Leuven, Belgium
⁷Nuclear Physics Institute of the Czech Academy of Sciences, Husinec-Řež CZ-25068 No. 130, Czech Republic
⁸Charles University, Faculty of Mathematics and Physics Ke Karlovu 3, 121 16 Praha 2, Czech Republic
⁹Laboratoire de Physique des deux Infinis Bordeaux (LP2IB), UMR 5797, CNRS/IN2P3, Université de Bordeaux, Chemin du Solarium, F-33170 Gradignan, France
¹⁰Departamento de Ingeniería Eléctrica y Centro de Estudios Avanzados en Física, Matemáticas y Computación, Universidad de Huelva, 21071 Huelva, Spain
¹¹Department of Physics, University of Regina, Regina, SK S4S 0A2, Canada
¹²Instituto de Física da Universidade de São Paulo, CEP 05508-090 São Paulo SP, Brazil
¹³Departamento de Ciencias Integradas y Centro de Estudios Avanzados en Física, Matemáticas y Computación, Universidad de Huelva, 21071 Huelva, Spain
¹⁴IRFU, CEA, Université Paris-Saclay, F-91191 Gif-sur-Yvette, France

^*Contact author: fuentes@lpccaen.in2p3.fr
^†Contact author: beatriz.fernandez.dominguez@usc.es
^‡Present address: Department of Physics, College of Humanities and Sciences, Nihon University, Sakurajosui 3, Setagaya-ku, Tokyo 156-8550, Japan and School of Physics, Beihang University, 37 Xueyuan Road, Haidian District, Beijing 100191, People’s Republic of China.

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Phys. Rev. Lett. 136, 212501 – Published 27 May, 2026

DOI: https://doi.org/10.1103/6gyv-qr54

Abstract

We present the first direct measurement of the $Z = 6$ shell gap in the neutron-rich ${}^{20}O$ nucleus. The one-proton removal transfer reaction ${}^{2}H ({}^{20}O, {}^{3}{He}) {}^{19}N$ has been studied using the ACTAR TPC setup at GANIL. The use of ACTAR TPC enabled the measurement of low-cross section proton-removal reactions while preserving resolution. Eight $p$ -hole states with $ℓ = 1$ were identified in ${}^{19}N$ accounting for total strengths of 86% and 72% of the $0 p_{3 / 2}$ and $0 p_{1 / 2}$ single-particle orbitals, respectively. The energies and spectroscopic factors of the measured states allowed to determine the proton spin-orbit splitting $π 0 p_{3 / 2} - π 0 p_{1 / 2}$ in ${}^{20}O$ . The $Z = 6$ shell gap has been established to be 5.30(14) MeV. These findings indicate a reduction of the $Z = 6$ shell gap while adding neutrons to the $s d$ -valence orbitals, consistent with the effects of the tensor force predicted by state-of-the-art shell model interaction SFO-tls while at variance with the emergence of a large $Z = 6$ gap observed in other studies.

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The Shell Model’s Shell Game

Published 27 May, 2026

A new experiment settles a controversy over proton and neutron energies in light nuclei.

Physical Review Letters

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Quenching of the $π 0 p_{3 / 2} - π 0 p_{1 / 2}$ Spin-Orbit Splitting in ${}^{20}O$ and the Effect of the Tensor Force

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The Shell Model’s Shell Game

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Quenching of the π0p3/2−π0p1/2 Spin-Orbit Splitting in O20 and the Effect of the Tensor Force

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The Shell Model’s Shell Game

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Quenching of the $π 0 p_{3 / 2} - π 0 p_{1 / 2}$ Spin-Orbit Splitting in ${}^{20}O$ and the Effect of the Tensor Force