Electron-Positron Pair Production In Coulomb Collisions Of Ultrarelativistic Sulfur Ions With Fixed Targets

Angular and momentum distributions have been measured for positrons from electron-positron pairs created in peripheral collisions of 6.4-TeV sulfur ions with fixed targets of Al, Pd, and Au. The data are compared with results of several theoretical treatments. Measured differential cross sections peak at low momentum (less-than-or-equal-to 1 MeV/c), extend significantly to much higher momenta (> 17 MeV/c), and concentrate sharply in the forward direction, along the ion-beam axis. Positron yields scale as the square of the target nuclear charge as predicted by theory.