Chiral Anomaly and the BaBar and Belle Measurements of the γγ~* → π~0 Transition Form Factor

摘要

The recent BaBar measurements of the γγ~* → π~0 transition form factor show spectacular deviation from perturbative QCD prediction for large space-like Q~2 up to 34GeV~2. In this talk, I would like to discuss a recent work on the chiral anomaly effects in the γγ~* → π~0 transition form factor F(Q~2) at large momentum squared Q~2. Using PCAC and the Adler-Bell-Jackiw chiral anomaly triangle graph, we find that, F(Q~2) at large Q~2 behaves as (m~2/Q~2) × (ln(Q~2/m~2))~2 and is in striking agreement with the BaBar data with m = 135MeV which also reproduces very well the CLEO data at lower Q~2. The new Belle measurements could also be fitted with m = 120MeV.