QCD Sum Rules and Pion Wavefunction

As a graduate student toward a master degree at the Institute of High-energy Physics, together with Tao Huang and Xiao-dong Xiang , I worked on problems related to the pion wavefuntion and its application to strong exclusive processes such as two-pion photoproduction and two-pion channel of charmonium decay[see pub_85]. We used the QCD sum rule technique to calculate moments of the pion wavefunction. Their values indicate a broad momentum distribution of the valence quarks inside a pion in contrary to a naive non-relativistic wavefunction. Because of such a broad distribution, the measured branch ratio of charmonium (1P) decaying into two pions can be accounted for.

We applied the same technique to heavy quark systems (quarkonium) and find that non-perturbative interaction (gluon condensate) combining the large mass reduces the wavefunction to a non-relativistic one.