Abstract

We present an analysis of the process e+e-→γ* or Z*→ππγ, in the kinematical region where s, the c.m. energy of the e+e- pair, is large but much below the Z-pole. The subprocess γ* or Z*→ππγ can be described by the convolution of the hard scattering coefficient γ* or Z*→qq̄γ and the general distribution amplitude of two pions qq̄→ππ. In the case of neutral pion, the production through γ* is the dominant process, which can therefore be used to access the generalized distribution amplitudes (GDAs) of the pion, especially their C-even parts. The γZ interference term provides an alternative approach to extract the weak mixing angle sin θW through measuring the helicity asymmetry in the process e+e-→π0π0γ. In the case of charged pion pair production, the Bremsstrahlung process dominates and its interference with e+e-→γ*→π+π-γ can be applied to study the process γ*→ππγ at the amplitude level. © 2006 The American Physical Society.