Common origin of the Belle-BESIII line-shape difference of $Λ_c^+\barΛ_c^-$, $D_s D_{s1}$ and $D_s D_{s2}^*$ from $e^+ e^-$ annihilation

Abstract

The longstanding Belle--BESIII discrepancies in the $e^+e^-\toΛ_c^+\barΛ_c^-$, $D_sD_{s1}(2536)$, and $D_sD_{s2}^{*}(2573)$ line shapes remain an unresolved puzzle, with enhancements observed by Belle that are absent or much weaker in the BESIII measurements. In this work, we propose a new mechanism based on the radiative production of higher charmonia to explain these differences. Such processes may contribute to Belle's initial-state radiation samples, and the luminosity normalization increases their contribution to the extracted cross sections. With the vector contributions scaled by BESIII data, a pseudoscalar charmonium $η_c(6S)$ contribution can describe the baryonic enhancement, while an introduced $χ_{c2}(5P)$ contribution can describe the enhancements in both meson channels. This mechanism offers a possible common explanation for these differences and, as a bonus, suggests a way to search for missing higher charmonia at Belle II.