T. Kishimoto, F. Khanam, T. Hayakawa, S. Ajimura, T. Itabashi, K. Matsuoka, S. Minami, Y. Mitoma, A. Sakaguchi, Y. Shimizu, K. Terai, T. Sato, H. Noumi, M. Sekimoto, H. Takahashi, T. Fukuda, W. Imoto, Y. Mizoi
We have searched for a bound state of kaon and pion denoted by $X$. The $X$ was conjectured to explain the so-called $\Theta^+$ resonance as a bound state of kaon, pion and nucleon. This model explains almost all properties of the $\Theta^+$, however, the model works only if the $K \pi$ interaction is strongly attractive. It is so strong that it could make a bound state $X$. Here we report a result of the search for the $X$ by using the $K^+ + N \rightarrow X^+ + N$ reaction at P$_K\sim$ 1.2 GeV/c. The $X^+ \rightarrow K^+ \gamma \gamma$ decay produces $K^+$ in momentum region where other processes cannot fill. We observed signature of the $X^+$ with statistical significance of 2 $\sigma$. Production cross section of $X$ with respect to that of $\pi^0$ is 1$\pm$0.5% if we take it as an evidence and 1.5% if we set an upper limit.
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http://arxiv.org/abs/1209.6216
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