Chiral Anomaly Effects and the BaBar Measurements of the $\gamma\gamma^{*} o \pi^{0}$ Transition Form Factor

摘要

The recent BaBar measurements of the $\gamma\gamma^{*}\to \pi^{0}$ transitionform factor show spectacular deviation from perturbative QCD prediction forlarge space-like $Q^{2}$ up to $34\,\rm GeV^{2}$. When plotted against $Q^{2}$,$Q^{2}F(Q^{2})$ shows steady increase with $Q^{2}$ in contrast with the flat$Q^{2}$ behavior predicted by perturbative QCD, and at $34\,\rm GeV^{2}$ ismore than 50% larger than the QCD prediction. Stimulated by the BaBarmeasurements, we revisit our previous paper on the cancellation of anomalyeffects in high energy processes $Z^{0}\to \pi^{0}\gamma$, $e^{+}e^{-}\to\pi^{0}\gamma$ and apply our results to the $\gamma^{*}\gamma\to \pi^{0}$transition form factor measured in the $e^{+}e^{-}\to e^{+}e^{-}\pi^{0}$process with one highly virtual photon. We find that, the transition formfactor $F(Q^{2})$ behaves as $(\frac{m^{2}}{Q^{2}})\times(\ln(Q^{2}/m^{2}))^{2}$ and produces a striking agreement with the BaBar datafor $Q^{2}F(Q^{2})$ with $m=132\,\rm MeV$ which also reproduces very well theCLEO data at lower $Q^{2}$.