The $\eta {-}^3$He scattering length revisited

Abstract

The possible existence of $\eta$-mesic nuclei poses an interesting and still open issue of research. Since the occurence of such $\eta$-nucleus bound states is reflected in the corresponding $\eta$-nucleus scattering length, we critically review the present knowledge for the $\eta$${}^3$He system. Specifically, we scrutinize the available experimental information for the reaction $p+d\to \eta {+}^3\mathrm{He}$ which is commonly used to extract the $\eta$${}^3$He scattering length. We point out several striking discrepancies between the various measurements. Subject to those inconsistencies we deduce a value of $a=|4.3\pm 0.3|+i(0.5\pm 0.5)$ fm.

8 pages, 9 figures, accepted for publication in Eur. Phys. J. A