Novel implementation of the multipole expansion to quarkonium hadronic transitions

Understand

We compute hadronic transitions between heavy quarkonium states with two, or one, pion/eta particles in the final state.

• We use the multipole expansion but not the twist expansion.
• The latter cannot be justified for the energy release of hadronic transitions between heavy quarkonium states with different principal quantum numbers.
• Instead, we use a counting based on the dimension of the interpolating field of the hybrid.