O(αsv2)corrections to hadronic and electromagnetic decays of 1S0 heavy quarkonium

We study O(alpha(s)v(2)) corrections to decays of S-1(0) heavy quarkonium into light hadrons and two photons within the framework of nonrelativistic QCD and find these O(alpha(s)v(2)) corrections to have significant contributions especially for the decay into light hadrons. With these new results, experimental measurements of the hadronic width and the gamma gamma width of eta(c) can be described more consistently. By fitting experimental data, we find the long- distance matrix elements of eta(c) to be |R-eta c (0)|(2) = 0.834(-0.197)(+0.281) GeV3 and < v(2)>eta(c) = 0.232(-0098)(+0.121) . Moreover, eta(c)(2S) is also discussed and the gamma gamma decay width is predicted to be 3: 34(-2.10)(+2.06) KeV.