"Hard-scattering" approach to very hindered magnetic-dipole transitions in quarkonium

Yu Jia, Jia Xu, Juan Zhang

For a class of hindered magnetic dipole ($M1$) transition processes, such as ${\rm Y}(3S)\to {\eta }_b+\gamma$ (the discovery channel of the ${\eta }_b$ meson), the emitted photon is rather energetic so…