Measurement of electron capture from electron-positron pair production in relativistic heavy ion collisions

We have used a novel new spectrometer to make the first observation and measurement of electron capture from ${\mathit{e}}^{+}$-${\mathit{e}}^{\mathrm{-}}$ pair production in relativistic heavy ion collisions. For a 0.96 GeV/nucleon ${\mathrm{U}}^{92+}$ beam the cross section for a Au target is 2.19(0.25) b, and the target Z dependence is ${\mathit{Z}}_{\mathit{t}}^{2.8\pm 0.25}$. We also measured the energy and angular distributions of the of the positrons, and for comparison, the cross section for ${\mathit{e}}^{+}$-${\mathit{e}}^{\mathrm{-}}$ pair production without capture is 3.30(0.65) b.