Colour-octet contributions to exclusive charmonium decays

J. Bolz, P. Kroll, G. A. Schuler

We investigate the theoretical uncertainties of $P$-wave charmonium decays into two pions, ${\chi }_{\stackrel{¸}{J}}\to {\pi }^{+}{\pi }^{-}$, ${\pi }^0{\pi }^0$. Constraining the pion distribution-amplitude from…