1. Resonance-like structure near the $\eta d$ threshold in the $\gamma{d}${$\to$}$\pi^0\eta{d}$ reaction
- Author
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Ishikawa, T., Fujimura, H., Fukasawa, H., Hashimoto, R., He, Q., Honda, Y., Iwata, T., Kaida, S., Kasagi, J., Kawano, A., Kuwasaki, S., Maeda, K., Masumoto, S., Miyabe, M., Miyahara, F., Mochizuki, K., Muramatsu, N., Nakamura, A., Nawa, K., Obara, Y., Ogushi, S., Okada, Y., Okamura, K., Onodera, Y., Ozawa, K., Sakamoto, Y., Sato, M., Shimizu, H., Sugai, H., Suzuki, K., Tajima, Y., Takahashi, S., Taniguchi, Y., Tsuchikawa, Y., Yamazaki, H., Yamazaki, R., and Yoshida, H. Y.
- Subjects
High Energy Physics::Experiment ,Nuclear Experiment - Abstract
To investigate the interaction between the nucleon $N$ and nucleon resonance $N(1535)1/2^-$, the $\eta d$ threshold structure connected to the isoscalar $S$-wave $N$-$N(1535)1/2^-$ system has been experimentally studied in the $\gamma{d}${$\to$}$\pi^0\eta{d}$ reaction at incident photon energies ranging from the reaction threshold to 1.15 GeV. A strong enhancement is observed near the $\eta d$ threshold over the three-body phase-space contribution in the $\eta d$ invariant-mass distribution. An analysis incorporating the known isovector resonance $\mathcal{D}_{12}$ with a spin-parity of $2^+$ in the $\pi^0d$ channel reveals the existence of a narrow isoscalar resonance-like structure with $1^-$ in the $\eta d$ system. Using a Flatt\'e parametrization, the mass is found to be $2.427_{-0.006}^{+0.013}$ GeV, close to the $\eta d$ threshold, and the width is $\left(0.029_{-0.029}^{+0.006}{\rm\ GeV}\right)+\left(0.00_{-0.00}^{+0.41}\right) p_\eta c$, where $p_\eta$ denotes the $\eta$ momentum in the rest frame of the $\eta d$ system. The observed structure would be attributed to a predicted isoscalar $1^-$ $\eta NN$ bound state from $\eta NN$ and $\pi NN$ coupled-channel calculation, or an $\eta d$ virtual state owing to strong $\eta d$ attraction., Comment: 6 pages, 3 figures
- Published
- 2021