Charge asymmetry of pions in the process $e^-e^+\to e^-e^+π^+π^-$

Details Charge asymmetry of pions in the process $e^-e^+\to e^-e^+π^+π^-$ Charge asymmetry of pions in the process $e^-e^+\to e^-e^+π^+π^-$

2000-12-06

arxiv.org/abs/hep-ph/0012069v1

Eur.Phys.J.C18:731-746,2001

Physics

High Energy Physics

High Energy Physics - Phenomenology

16 pages, 10 figures, LaTeX, style files for EPJC included

Scientific paper

10.1007/s100520100583

The study of the charge asymmetry of produced particles allows to investigate the interference of different production mechanisms and to determine new features of the corresponding amplitudes. In the process $e^- e^+ \to e^- e^+ \pi^+ \pi^-$ the two-pion system is produced via two mechanisms: two-photon (C-even state) and bremsstrahlung (C-odd state) production. We study the charge asymmetry of pions in a differential in the pion momenta cross section originating from an interference between these two mechanisms. At low effective mass of dipions this asymmetry is directly related to the s- and p-phases of elastic $\pi\pi$ scattering. At higher energies it can give new information about the $f_0$ meson family, $f_2(1270)$ meson, etc. The asymmetry is expressed via the pion form factor $F_\pi$ and helicity amplitudes $M_{ab}$ for the subprocess $\gamma^*\gamma\to \pi^+\pi^-$ as $\sum G_{ab}{\rm Re}(F_\pi^*M_{ab})$ where we have calculated analytically the coefficients $G_{ab}$ for the region giving the main contribution to the effect. Several distributions of pions are presented performing a numerical analysis in a model with point-like pions. In the region near the dipion threshold the asymmetry is of the order of 1%. We show that with suitable cuts the signal to background ratio can be increased up to about 10%.

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