An analysis of the reaction pp --> ppηnear threshold

Abstract

It is shown that most of the available data on the $pp\to pp\hat{I}\cdot$ reaction, including the invariant mass distributions in the $pp\to pp\hat{I}\cdot$ reaction recently measured at COSY, can be understood in terms of the partial-wave amplitudes involving final $pp$ $S$ and $P$ states and the $\hat{I}\cdot$ meson s-wave. This finding, together with the fact that results within a meson--exchange model are especially sensitive to the details of the excitation mechanism of the $S_{11}(1535)$ resonance, demonstrates the possibility of investigating the properties of this resonance in $NN$ collisions. The spin correlation function $C_{xx}$ is shown to disentangle the $S$- and $P$-wave contributions. It is also argued that spin correlations may be used to help constrain the contributions of the amplitudes corresponding to the final $pp$ ${}^3{P}_0$

10 pages, 7 figures, minor revision with one additional figure