Resonance-like structure near the <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>η</mi><mi>d</mi></mrow></math> threshold in the <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>γ</mi><mi>d</mi><mo>→</mo><msup><mi>π</mi><mn>0</mn></msup><mi>η</mi><mi>d</mi></mrow></math> reaction

T. Ishikawa; H. Fujimura; H. Fukasawa; R. Hashimoto; Q. He; Y. Honda; T. Iwata; S. Kaida; J. Kasagi; A. Kawano; S. Kuwasaki; K. Maeda; S. Masumoto; M. Miyabe; F. Miyahara; K. Mochizuki; N. Muramatsu; A. Nakamura; K. Nawa; Y. Obara; S. Ogushi; Y. Okada; K. Okamura; Y. Onodera; K. Ozawa; Y. Sakamoto; M. Sato; H. Shimizu; H. Sugai; K. Suzuki; Y. Tajima; S. Takahashi; Y. Taniguchi; Y. Tsuchikawa; H. Yamazaki; R. Yamazaki; H. Y. Yoshida

doi:10.1103/PhysRevC.104.L052201

Letter

Resonance-like structure near the $η d$ threshold in the $γ d \to π^{0} η d$ reaction

T. Ishikawa ^1,*, H. Fujimura^1,†, H. Fukasawa¹, R. Hashimoto^1,‡, Q. He^1,§, Y. Honda¹, T. Iwata², S. Kaida¹, J. Kasagi¹ et al.

A. Kawano³, S. Kuwasaki¹, K. Maeda⁴, S. Masumoto⁵, M. Miyabe¹, F. Miyahara^1,∥, K. Mochizuki¹, N. Muramatsu¹, A. Nakamura¹, K. Nawa¹, Y. Obara⁵, S. Ogushi¹, Y. Okada¹, K. Okamura¹, Y. Onodera¹, K. Ozawa⁶, Y. Sakamoto³, M. Sato¹, H. Shimizu¹, H. Sugai^1,¶, K. Suzuki^1,**, Y. Tajima², S. Takahashi¹, Y. Taniguchi¹, Y. Tsuchikawa^1,††, H. Yamazaki^1,‡‡, R. Yamazaki¹, and H. Y. Yoshida²

¹Research Center for Electron Photon Science (ELPH), Tohoku University, Sendai 982-0826, Japan
²Department of Physics, Yamagata University, Yamagata 990-8560, Japan
³Department of Information Science, Tohoku Gakuin University, Sendai 981-3193, Japan
⁴Department of Physics, Tohoku University, Sendai 980-8578, Japan
⁵Department of Physics, University of Tokyo, Tokyo 113-0033, Japan
⁶Institute of Particle and Nuclear Studies (IPNS), High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801, Japan

^*Corresponding author: ishikawa@lns.tohoku.ac.jp
^†Present address: Department of Physics, Wakayama Medical University, Wakayama 641-8509, Japan.
^‡Present address: Institute of Materials Structure Science (IMSS), KEK, Tsukuba 305-0801, Japan.
^§Present address: Department of Nuclear Science and Engineering, Nanjing University of Aeronautics and Astronautics (NUAA), Nanjing 210016, China.
^∥Present address: Accelerator Laboratory, KEK, Tsukuba 305-0801, Japan.
^¶Present address: Gunma University Initiative for Advanced Research (GIAR), Maebashi 371-8511, Japan.
^**Present address: The Wakasa Wan Energy Research Center, Tsuruga 914-0192, Japan.
^††Present address: J-PARC Center, Japan Atomic Energy Agency (JAEA), Tokai 319-1195, Japan.
^‡‡Present address: Radiation Science Center, KEK, Tokai 319-1195, Japan.

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Phys. Rev. C 104, L052201 – Published 29 November, 2021

DOI: https://doi.org/10.1103/PhysRevC.104.L052201

Abstract

To investigate the interaction between the nucleon $N$ and nucleon resonance $N (1535) 1 / 2^{-}$ , the $η d$ threshold structure connected to the isoscalar $S$ -wave $N − N (1535) 1 / 2^{-}$ system has been experimentally studied in the $γ d \to π^{0} η d$ reaction at incident photon energies ranging from the reaction threshold to 1.15 GeV. A strong enhancement is observed near the $η d$ threshold over the three-body phase-space contribution in the $η d$ invariant-mass distribution. An analysis incorporating the known isovector resonance $D_{12}$ with a spin parity of $2^{+}$ in the $π^{0} d$ channel reveals the existence of a narrow isoscalar resonance-like structure with $1^{-}$ in the $η d$ system. Using a Flatté parametrization, the mass is found to be $2 . 427_{- 0.006}^{+ 0.013}$ GeV, close to the $η d$ threshold, and the width is $(0 . 029_{- 0.029}^{+ 0.006} GeV) + (0 . 00_{- 0.00}^{+ 0.41}) p_{η} c$ , where $p_{η}$ denotes the $η$ momentum in the rest frame of the $η d$ system. The observed structure would be attributed to a predicted isoscalar $1^{-} η N N$ bound state from $η N N$ and $π N N$ coupled-channel calculation, or an $η d$ virtual state owing to strong $η d$ attraction.

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Resonance-like structure near the $η d$ threshold in the $γ d \to π^{0} η d$ reaction

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Resonance-like structure near the ηd threshold in the γd→π0ηd reaction

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Resonance-like structure near the $η d$ threshold in the $γ d \to π^{0} η d$ reaction