$\Lambda \bar{\Lambda }$ final-state interaction in the reactions $e^{+}{e}^{-}\to \varphi \Lambda \bar{\Lambda }$ and $e^{+}{e}^{-}\to \eta \Lambda \bar{\Lambda }$

Abstract

Near-threshold $\Lambda \bar{\Lambda }$ mass spectra for the reactions $e^{+}{e}^{-}\to \eta \Lambda \bar{\Lambda }$ and $e^{+}{e}^{-}\to \varphi \Lambda \bar{\Lambda }$ are investigated with an emphasis on the role played by the interaction in the $\Lambda \bar{\Lambda }$ system. A variety of $\Lambda \bar{\Lambda }$ potential models is employed that have been established in the analysis of data on $p\bar{p}\to \Lambda \bar{\Lambda }$ in the past. It is shown that the near-threshold enhancement observed for the two $e^{+}{e}^{-}$ reactions can be reproduced by considering the $\Lambda \bar{\Lambda }$ final-state interaction in the partial waves suggested by the helicity-angle analysis of the experiments. For $e^{+}{e}^{-}\to \eta \Lambda \bar{\Lambda }$ the same $\Lambda \bar{\Lambda }$ $S$-wave interaction as in $e^{+}{e}^{-}\to \Lambda \bar{\Lambda }$ is relevant and with it a consistent description of the pertinent measurements can be achieved. It is pointed out that a nonzero threshold cross section as observed for the latter reaction is not supported by the new $\eta \Lambda \bar{\Lambda }$ data.

Comments: 8 pages, 5, figures