${\pi }^{-}p\to {\eta }^{(\mathrm{\prime })}{\pi }^{-}p$ in the double-Regge region

The production of ${\eta }^{(\mathrm{\prime })}\pi$ pairs constitutes one of the golden channels to search for hybrid exotics, with explicit gluonic degrees of freedom. Understanding the dynamics and backgrounds associated to ${\eta }^{(\mathrm{\prime })}\pi$ production above the resonance region is required to impose additional constraints to the resonance extraction. We consider the reaction ${\pi }^{-}p\to {\eta }^{(\mathrm{\prime })}{\pi }^{-}p$ measured by COMPASS. We show that the data in $2.4<m_{{\eta }^{(\mathrm{\prime })}\pi }<3.0$ GeV can be described by amplitudes based on double-Regge exchanges. The angular distribution of the meson pairs, in particular in the ${\eta }^{\mathrm{\prime }}\pi$ channel, can be attributed to flavor singlet exchanges, suggesting the presence of a large gluon content that couples strongly to the produced mesons.