Pion pair production in e+e- annihilation

We present an analysis of the process e(+)e(-)->gamma(*) or Z(*)->pi pi gamma, in the kinematical region where root s, the c.m. energy of the e(+)e(-) pair, is large but much below the Z-pole. The subprocess gamma(*) or Z(*)->pi pi gamma can be described by the convolution of the hard scattering coefficient gamma(*) or Z(*)-> q (q) over bar gamma and the general distribution amplitude of two pions q (q) over bar ->pi pi. In the case of neutral pion, the production through gamma(*) 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 gamma Z interference term provides an alternative approach to extract the weak mixing angle sin theta(W) through measuring the helicity asymmetry in the process e(+)e(-)->pi(0)pi(0)gamma. In the case of charged pion pair production, the Bremsstrahlung process dominates and its interference with e(+)e(-)->gamma(*)->pi(+)pi(-)gamma can be applied to study the process gamma(*)->pi pi gamma at the amplitude level.