Potential of the reaction $e^+e^-\to p\bar{p}π^0$ for constructing higher $ρ$-meson spectroscopy above 2.4 GeV

Abstract: The spectrum of light unflavored vector mesons above 2.4 GeV has not yet been firmly established experimentally. In this work, we demonstrate that the process $e^+e^- \to p\bar{p}\pi$ serves as a particularly promising channel as a probe for higher isovector $\rho$ excitations. In contrast to typical electron-positron annihilation processes into purely light-meson final states, the reaction $e^+e^- \to p\bar{p}\pi$ benefits from a relatively low continuum background, on the order of $(50\sim100)~\text{pb}$ around 2.4 GeV, which enhances the visibility of even modest resonance contributions. In addition, the comparatively high production threshold further suppresses potential contamination from lower $\rho$-meson excitations. Our analysis based on effective Lagrangian approach indicates that the observed lineshape of the $e^+e^- \to p\bar{p}\pi$ cross section measured by BESIII can be naturally interpreted by including the $\rho(5S)$ and $\rho(6S)$ contributions, namely the fourth and fifth radial excitations of $\rho(770)$. In particular, the pronounced rise of the cross section near 2.4 GeV provides strong evidence for the contribution of $\rho(5S)$ signal. Their branching ratios to the $p\bar{p}\pi$ final state are found to be below 4\%, which do not contradict with usual expectations. In addition, we evaluate pion-induced production of these two $\rho$-meson states as a complementary probe, offering useful guidance for the relevant experiments such as COMPASS.