Search for eta-mesic 3He in non-mesonic final states
In May-June 2014, the experiment devoted to the search for the bound state of the $η$ meson and $^3$$He$ nucleus has been performed at COSY accelerator in Research Center Jülich in Germany with WASA-at-COSY facility. The excitation functions for $pd\rightarrow^3$$He2γ$, $pd\rightarrow^3$$He6γ$, $pd\rightarrow pppπ^{-}$, $pd\rightarrow ppnπ^{0}$, $pd\rightarrow dnπ^{-}$, $pd\rightarrow dpπ^{0}$, $pd\rightarrow pd$, and $pd\rightarrow ppn$ reactions have been measured in the vicinity of the $η$ meson production threshold. The experiment was carried out using COSY ramped proton beam and deuterium pellet target. The beam momentum varied continuously in the range of $1.426-1.635~GeV/c$ corresponding to $^3$$He-η$ excess energy range from $-70$ to $+30~MeV$. The analysis of the obtained excitation functions for the $pd\rightarrow^3$$Heη$ indicate slightly the signal from the bound state for $Γ>20~MeV$ 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 $η$-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 $η$ 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 $15~nb$ within the binding energy range from $0$ to $60~MeV$ and the width from $2.5$ to $40~MeV$.