Measurement of yy Transition Form Factor at Belle
We report a measurement of exclusive π0 production in the process of e+e- scattering in a kinematic region where the π0 and the final-state electron or positron are detected (i.e. tagged). We use a 759 fb-1 data sample recorded with the Belle detector at the KEKB asymmetric-energy e+e- collider to measure the yy transition form factor F(Q2) in the momentum transfer region 4 GeV2 ≤ Q2 ≤ 40 GeV2.
The reported values of Q2|F(Q2)| agree well with previous measurements at Q2 ≤ 9 GeV2, are reasonably consistent with recent results reported by the BaBar experiment but do not support their hypothesis of the rapid increase of Q2|F(Q2)| at higher Q2 values. We also discuss the prospects of performing a similar analysis with the future BELLE II data.