Search for $\eta$-bound Nuclei

Abstract

The $\eta$ meson can be bound to atomic nuclei. Experimental search is discussed in the form of final state interaction for the reactions $dp\to {}^3\text{He}\eta$ and $dd\to {}^4\text{He}\eta$. For the latter case tensor polarized deuterons were used in order to extract the s-wave strength. For both reactions complex scattering lengths are deduced: $a_{{}^3\mathrm{He}\eta }=\left[\pm \left(10.7\pm 0.8_{-0.5}^{+0.1}\right)+i\cdot \left(1.5\pm 2.6_{-0.9}^{+1.0}\right)\right]$ fm and $a_{{}^4\text{He}\eta }=\left[\pm \left(3.1\pm 0.5\right)+i\cdot \left(0\pm 0.5\right)\right]$ fm. In a two-nucleon transfer reaction under quasi-free conditions, $p^{27}\text{Al}\to {}^3\text{He}X$, was investigated. The system $X$ can be the bound ${}^{25}\text{Mg}\otimes \eta$ at rest. When a possible decay of an intermediate $N^{\ast }/1535)$ is required, a highly significant bump shows up in the missing mass spectrum. The data give for a bound state a binding energy of 13.3$\pm$1.6 MeV and a width of $\sigma$=4.4$\pm$1.3 MeV.

Comments: Presented at the International Symposium on Mesic Nuclei, Kraków, Poland, June 16, 2010