Observation of Bhabha scattering in the center-of-mass kinetic-energy range 342 to 845 keV

Abstract

Positrons from a ${}_{}{}^{27}{}_{}{}^{}\mathrm{Si}$ source, obtained through the reaction ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$(p,n${)\mathrm{}}^{27}$Si, were scattered off electrons in a target of polyethylene, and $e^{+}$ $e^{\mathrm{-}}$ coincidences were detected in a pair of plastic scintillators. The detector aperatures were restricted to accept only events corresponding to maximum momentum transfer at center-of-mass angle π/2. The variation with energy of the corresponding laboratory angle was utilized to obtain the scattering excitation function from the continuous positron spectrum. Center-of-mass kinetic energies in the $e^{+}$ $e^{\mathrm{-}}$ system covered the range 342 to 845 keV.