1. Angular distribution in s-channel formation of the pentaquark $\Theta^+$ baryon
- Author
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DIANA Collaboration, Barmin, V. V., Asratyan, A. E., Curceanu, C., Davidenko, G. V., Guaraldo, C., Kubantsev, M. A., Larin, I. F., Matveev, V. A., Shebanov, V. A., Shishov, N. N., Sokolov, L. I., and Tarasov, V. V.
- Subjects
High Energy Physics - Experiment ,Nuclear Experiment - Abstract
Using the DIANA data on the charge-exchange reaction $K^+n \rightarrow pK^0$ on a bound neutron, in which the s-channel formation of the pentaquark baryon $\Theta^+(1538)$ has been observed, we analyze the dependence of the background-subtracted $\Theta^+ \rightarrow pK^0$ signal on the $K^0$ emission angle in the $pK^0$ rest frame. In order to describe the observed $\cos\Theta_K^\mathrm{cms}$ distribution, invoking the interference between the nonresonant s-wave and the $\Theta^+$-mediated higher-wave contributions to the amplitude of the charge-exchange reaction is required at a 2.8$\sigma$ level. The spin--parity assignment of 1/2$^-$ for the $\Theta^+$ baryon is ruled out at a statistical level of 2.9 standard deviations. A physically-meaningful selection in $\cos\Theta_K^\mathrm{cms}$ based on the observed angular dependence of the $\Theta^+ \rightarrow pK^0$ signal allows to boost the statistical significance of the signal up to 7.1 standard deviations. This is far in excess of previously reported signals and renders the $\Theta^+$ existence more credible., Comment: 13 pages, 7 figures
- Published
- 2015