Relativistic effects and angular dependence in the reactionp¯p→π−π+

We present a fit to the low energy antiproton ring at CERN data on $\overline{p}p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{+}$ differential cross sections and analyzing powers motivated by relativistic considerations. Within a quark model describing this annihilation, we argue, since the pions are highly energetic, that relativistic effects cannot be neglected. The intrinsic pion wave functions are Lorentz transformed to the center-of-mass frame. This change in quark geometry gives rise to additional angular dependence in the transition operators and results in a relative enhancement of higher $J\ensuremath{\geqslant}2$ partial wave amplitudes. The fit to the data is improved significantly.