Speaker
Dr
Kouhei Hasegawa
(Desy Zeuthen, Theory group)
Description
We calculate the light-by-light scattering type two-loop QCD corrections due to the light quark loops in the
para-charmonium decays $eta_{c} rightarrow gamma gamma$ and $eta_{c} rightarrow g g$. We replace
the mass of the internal charm quarks by an artificial large mass and obtain the result as a series in the
large mass. The obtained series can be transformed into the good convergent ones by a change of the
expansion parameter. The results are supported by two other methods to improve the convergence. We also
observe that the color singlet state of $eta_{c}$ eliminates the potential divergences in the two-loop QCD
corrections. The obtained corrections to the modes $eta_{c} rightarrow gamma gamma$ and $eta_{c}
rightarrow g g$ account for -1.25% and -0.73% of the tree level values, respectively.
Based on preprint
hep-ph/0610415
Primary author
Dr
Kouhei Hasegawa
(Desy Zeuthen, Theory group)
Co-author
Mr
Pak Alexey
(University of Alberta)
