Hindered magnetic dipole transition in the covariant light-front approach

Abstract

Hindered magnetic dipole transitions $Υ(nS)\to γη_b(n'S)$ are studied in the covariant light-front approach. Compared with the allowed magnetic dipole transitions, we find that results for hindered magnetic dipole transitions are sensitive to heavy quark mass and shape parameters of the light-front wave functions. It is possible to tune the parameters so that the predictions of branching fractions of $Υ(2S,3S)\toγη_b$ are consistent with the recent experimental data, but the relevant decay constant of $η_b$ is much smaller than that of $Υ(1S)$. We also generalize the investigation to the charmonium sector and find the the same conclusion.

8 pages, 1 figure