Quarkonium chromo-polarizability from the decays $J/\psi ({\rm Y})\to \pi \pi {\ell }^{+}{\ell }^{-}$

Abstract

It is pointed out that the diagonal amplitude of the $E1-E1$ chromo-electric interaction with soft gluon fields (chromo-polarizability) can be measured directly for the $J/\psi$ and ${\rm Y}$ resonances in the decays $J/\psi \to \pi \pi {\ell }^{+}{\ell }^{-}$ and ${\rm Y}\to \pi \pi {\ell }^{+}{\ell }^{-}$ with soft pions. For the $J/\psi$ this amplitude is often discussed in connection with the $J/\psi$ interaction with nuclear matter, while for the ${\rm Y}$ the chromo-polarizability enters the estimates of the non-perturbative mass shift of the resonance relevant to precision determination of the $b$ quark mass from the ${\rm Y}$ mass.

Comments: 6 pages