Observation of the radiative decays of $\Upsilon(1S)$ to $\chi_{c1}$
Pavel V. Oskin, S. Pardi, Martin Ritter, Armine Rostomyan et autres
We report the first observation of the radiative decay of the $\Upsilon(1S)$ into a charmonium state. The statistical significance of the observed signal of $\Upsilon(1S) \to \gamma \chi_{c1}$ is 6.3 standard deviations including systematics. The branching fraction is calculated to be Br($\Upsilon(1S) …