First Measurement of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mrow><mi>K</mi></mrow><mrow><mo>−</mo></mrow></msup></mrow></math> Escape Cross Section in the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mmultiscripts><mrow><mi mathvariant="normal">C</mi></mrow><mprescripts></mprescripts><none></none><mrow><mn>12</mn></mrow></mmultiscripts><mo stretchy="false">(</mo><msup><mrow><mi>K</mi></mrow><mrow><mo>−</mo></mrow></msup><mo>,</mo><mi>p</mi><mo stretchy="false">)</mo></mrow></math> Reaction

J-PARC E42 Collaboration; Fumiya Oura; Yudai Ichikawa; Junko Yamagata-Sekihara; Jung Keun Ahn; Sung Wook Choi; Manami Fujita; Takeshi Harada; Shoichi Hasegawa; Shuhei Hayakawa; Kenneth Hicks; Satoru Hirenzaki; Sang Hoon Hwang; Ken’ichi Imai; Yuji Ishikawa; Woo Seung Jung; Shunsuke Kajikawa; Kento Kamada; Byung Min Kang; Shin Hyung Kim; Tomomasa Kitaoka; Jaeyong Lee; Jong Won Lee; Koji Miwa; Taito Morino; Tamao Sakao; Hiroyuki Sako; Masayoshi Saito; Susumu Sato; Toshiyuki Takahashi; Kiyoshi Tanida; Hirokazu Tamura; Mifuyu Ukai; Shunsuke Wada; Takeshi O. Yamamoto; Seongbae Yang

doi:10.1103/y6wr-rqjp

First Measurement of the $K^{-}$ Escape Cross Section in the ${}^{12}C (K^{-}, p)$ Reaction

Fumiya Oura ^1,2,*, Yudai Ichikawa ^2,1, Junko Yamagata-Sekihara ³, Jung Keun Ahn ⁴, Sung Wook Choi⁴, Manami Fujita ⁵, Takeshi Harada ⁶, Shoichi Hasegawa ¹, Shuhei Hayakawa ² et al. (J-PARC E42 Collaboration)

Shuhei Hayakawa ², Kenneth Hicks⁷, Satoru Hirenzaki ⁸, Sang Hoon Hwang⁹, Ken’ichi Imai ^1,6, Yuji Ishikawa², Woo Seung Jung ¹, Shunsuke Kajikawa², Kento Kamada ², Byung Min Kang ⁴, Shin Hyung Kim ¹⁰, Tomomasa Kitaoka², Jaeyong Lee ¹¹, Jong Won Lee¹², Koji Miwa ^2,13, Taito Morino ², Tamao Sakao², Hiroyuki Sako¹, Masayoshi Saito², Susumu Sato¹, Toshiyuki Takahashi ¹³, Kiyoshi Tanida ¹, Hirokazu Tamura ^2,1, Mifuyu Ukai^13,2, Shunsuke Wada², Takeshi O. Yamamoto¹, and Seongbae Yang⁴ (J-PARC E42 Collaboration)

¹Advanced Science Research Center, Japan Atomic Energy Agency, Tokai 319-1195, Japan
²Department of Physics, Tohoku University, Sendai 980-8578, Japan
³Kyoto Sangyo University, Kyoto, Japan
⁴Department of Physics, Korea University, Seoul 02841, Republic of Korea
⁵Department of Physics, The University of Tokyo, Tokyo 113-0033, Japan
⁶Department of Physics, Kyoto University, Kyoto 606-8502, Japan
⁷Department of Physics and Astronomy, Ohio University, Athens, Ohio 45701, USA
⁸Nara Women’s University, Nara 630-8506, Japan
⁹Korea Research Institute of Standards and Science, Daejeon 34113, Republic of Korea
¹⁰Department of Physics, Kyungpook National University, Daegu 41566, Republic of Korea
¹¹Department of Physics and Astronomy, Seoul National University, Seoul 08826, Republic of Korea
¹²Department of Physics Education, Jeonbuk National University, Jeonju 54896, Republic of Korea
¹³Institute of Particle and Nuclear Studies, High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801, Japan

^*Contact author: fumiya.oura@gmail.com

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Phys. Rev. Lett. 137, 132501 – Published 22 September, 2026

DOI: https://doi.org/10.1103/y6wr-rqjp

Abstract

We investigated the $\bar{K}$ -nucleus interaction through the simultaneous measurement of the inclusive ${}^{12}C (K^{-}, p)$ and exclusive $K^{-}$ escape ${}^{12}C (K^{-}, p K_{esc}^{-})$ reactions at $1.8 GeV / c$ at J-PARC. The present measurement explicitly focuses on the $K^{-}$ escape process for the first time, successfully accomplishing a direct experimental determination of the imaginary part of the $K^{-}$ optical potential. The differential cross section for the $K^{-}$ escape reaction was determined to be $436 \pm 6 (stat .) \pm 44 (syst .) μ b / sr$ . A simultaneous likelihood fit yielded real and imaginary potential strengths of $V_{0} = - 72_{- 5}^{+ 3} (stat .)_{- 8}^{+ 0} (syst .) MeV$ and $W_{0} = - 100_{- 1}^{+ 7} (stat .)_{- 16}^{+ 0} (syst .) MeV$ at the nuclear center, respectively. The derived $W_{0}$ is significantly stronger than that predicted by theoretical models based on one-nucleon processes, ssuggesting possible contributions from processes involving multiple nucleons.

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First Measurement of the $K^{-}$ Escape Cross Section in the ${}^{12}C (K^{-}, p)$ Reaction

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First Measurement of the K− Escape Cross Section in the C12(K−,p) Reaction

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First Measurement of the $K^{-}$ Escape Cross Section in the ${}^{12}C (K^{-}, p)$ Reaction