Threshold behavior of electron pair production inp-Be collisions

We report on the measurements of electron pair production in p-Be collisions at 1.0, 2.1, and 4.9 GeV beam kinetic energies. The invariant-mass and transverse-momentum spectra are presented, along with the total cross sections. A rapid decrease in the integrated cross section is observed as the beam energy is reduced. Comparison of the excitation function for dielectron ($e^{+}$ $e^{\mathrm{-}}$) and dipion (${\pi }^{+}$ ${\pi }^{\mathrm{-}}$) production suggests that the dominant production mechanism at beam kinetic energies 2.1 and 4.9 GeV may be ${\pi }^{+}$ ${\pi }^{\mathrm{-}}$ annihilation.