Search for eta-mesic 3He in non-mesonic final states

Abstract

In May-June 2014, the experiment devoted to the search for the bound state of the $\eta$ meson and ${}^3$$He$ nucleus has been performed at COSY accelerator in Research Center Jülich in Germany with WASA-at-COSY facility. The excitation functions for $pd{\to }^3$$He2\gamma$, $pd{\to }^3$$He6\gamma$, $pd\to ppp{\pi }^{-}$, $pd\to ppn{\pi }^0$, $pd\to dn{\pi }^{-}$, $pd\to dp{\pi }^0$, $pd\to pd$, and $pd\to ppn$ reactions have been measured in the vicinity of the $\eta$ meson production threshold. The experiment was carried out using COSY ramped proton beam and deuterium pellet target. The beam momentum varied continuously in the range of $1.426-1.635GeV/c$ corresponding to ${}^3$$He-\eta$ excess energy range from $-70$ to $+30MeV$. The analysis of the obtained excitation functions for the $pd{\to }^3$$He\eta$ indicate slightly the signal from the bound state for $\Gamma >20MeV$ and $B\in [0;15]MeV$. However, the observed indication is in the range of the systematic error. Therefore the final conclusion of this thesis is that no narrow structure that could be interpreted as $\eta$-mesic nucleus was observed in both excitation curves. Thus, the upper limit for the total cross section of the bound state formation was estimated assuming that the $\eta$ decay branching ratios in the bound state is the same as in free space. The upper limit at the $90\%$ confidence level varies from $2$ to $15nb$ within the binding energy range from $0$ to $60MeV$ and the width from $2.5$ to $40MeV$.

References in corpus (5)

• Measurement of the dp -->3He eta reaction near threshold
• Is there an eta-3He quasi--bound state ?
• Search for eta-mesic 4He in the dd->3He n pi0 and dd->3He p pi- reactions with the WASA-at-COSY facility
• Precision study of the d+p->3He+eta reaction for excess energies between 20 and 60 MeV
• Unresolved issues in the search for eta-mesic nuclei