Production of prompt positrons at low transverse momentum in 63 GeV pp collisions at the CERN intersecting storage rings

Abstract The production of inclusive prompt positrons in pp collisions at √ s = 63 GeV and θ cm = 90° has been measured over the p T interval 0.08 T GeV c . The e / π ratio rises from ∼ 2 × 10 −4 at p T = 0.9 GeV c to ∼ 1 × 10 −3 at p T = 0.1 GeV c . This is a factor of 6 higher than would be expected from the sum of hadronic bremsstrahlung and the semileptonic decay of charm.